L8148 Aquastat Installation & Repair FAQs

Reader Q&A on L8148 aquastats, all models

L8148 Aquastat HIGH & DIFFERENTIAL FAQs

What is the differential on a high limit honeywell L8148A aquastat

What is the differential on a high limit honeywell L8148A aquastat - On 2022-11-24 by phil

Reply by InspectApedia (Editor) - 15 degF. down to 5 degF for Aquastats that have Differential that is hard-wired, i.e. not adjustable

@phil,

Honeywell describes the L8148A control (without mentioning a differential):

A call for heat by the thermostat starts both the burner and the circulator.

When boiler-water temperature exceeds the high-limit settings, the burner circuit is broken; the circulator continues to operate during the thermostat call for heat.

You would think that means that at ANY temperature more than just a few degrees below the HI (enough to avoid short cycling) the burner will start.

I've read through generations of L8148 documentation without finding a number. I think that's no accident as it may not be precise.

So the answer is: there is no single right answer as the company changed its fixed differential gap over the years, (often just 5 degF)

Currently, depending on the specific model, the 8148 will have a fixed DIFF of either 8 degF or 15 degF.

A reasonable guess is that depending on your aquastat's model and age if the model is using a fixed or hard-wired differential it will be 5 degF. to 15 degF - remember this is just for a control that has no adjustable differential and no standard LO limit control (though some models have provision for adding a LO limit).

The Standard Scale Range: 180°F to 240°F (82°C to 116°C).

The optional operating range is 140°F to 240°F (60°C to 116°C)

If you don't have it, you can download the manual for your L8148 aquastat

at

HONEYWELL L8148A,E,J AQUASTAT® RELAYS (Controllers), product data & installation, operation manual including L8148 wiring diagrams [PDF]

L8148 Aquastat Wiring FAQs

For a Gas boiler do I use the r,w terminal? or r,b terminal on the L8148?

When wiring a hi limit aquastat to my gas boiler valve do I use the r,w terminal?

Or r,b?

Also the line feeds from a transformer, to gas valve, to L4006A thermostat then to the hi limit( L6006C) On 2020-03-10 by Angelina

Reply by (mod) -

Angelina

In the ARTICLE INDEX links or at CONTINUE READING near the end of this page please see the live link

AQUASTAT L6006A HONEYWELL GUIDE - for proper wiring instructions for that limit control.

Typically R and W are the two thermostat wire connections

Watch out: if you are not trained on safe and proper electrical wiring you could be shocked or killed or could damage the equipment or cause a fire.

Details needed for re-wiring my Honeywell zone valves/Honeywell Aquastat/and thermostat wiring

Thanks for the prompt reply Dan. Honeywell doesn't seem to have the chat option anymore, so I guess I'll call their 800 support number this coming week.

I'll come back & let you know how I make out and what they say.

I find myself re-wiring my Honeywell zone valves/Honeywell Aquastat/and thermostat wiring at my gas boiler furnace. (It's a long story!).

My burner uses a low voltage (24v AC) gas valve, and it is a 4 zone valve system with 2 additional 24v AC transformers for the thermostats and Honeywell zone valves.

I also have 3 Honeywell V8043E and 1 V8043F valves. I'm an ex-auto tech and trainer so I "get" DC schematics, and have done a fair amount of 110/220 AC electrical wiring & fixes to be knowledgeable but by no means an authority.

I find the Honeywell schematics to be very helpful, but at the same time lacking and since none of the diagrams in either the Aquastat or zone valve sheets matched my system,

I re-drew what I thought my system schematic should look like, in a format that I was familiar with. Can someone have a look to see if what I have drawn is theoretically correct? The two things I had the most problem with were properly

isolating the 3 AC transformer circuits, and

which 2 Aquastat terminals on the AC circuit going to the zone end switches and back to close the burner & circulator relay (specifically TV and T- Does it matter if what I show connected to T were connected to either W or TP?)

Thanks to anyone having a look at my diagram and offering advice or corrections.

One last puzzle to me .. what the heck are the 1K2 & 1K3 items on the Honeywell sheets? Switches or capacitors?

Image lost, our foul-up; please re-post it if you can. - On 2020-01-10 by Jim Davis

Reply by (mod) -

Thanks for the follow-up; do keep us posted.

Yes it's disappointing that as business models shift to very high volumes customer service is on the wane.

Reply by (mod) - zone valve wiring connections to the L8148

Gee Jim I hope your confidence in me will increase when I admit I don't know something. Rather than guess I'd feel safer if we (that really means you) give Honeywell a call or chat directly with this schematic and question. [Click to enlarge any image]

Honeywell Technical Support: 1-877-841-2840 or (800) 645-7492 or for international customers 00 1 480-353-3020

Website: www.honeywellaidc.com/working-with-us/contact-technical-support

Honeywell Chat:
honeywell.com/Pages/contact-us.aspx

Honeywell Email:
sales@HoneywellStore.com

Corporate Office Address:
Honeywell International
101 Columbia Road Mailstop - M6/LM
Morristown , NJ 07962
USA

let me know how you're treated and what you're told as that will surely help other readers.

In general, at the zone valve the thermostat operates the valve from the two T- terminals (not polarized) and the zone motor's end-switch will turn on the circulator wired to two C terminals.

I don't know, without more reading, what the 1K1 & 1K3 are.

 

How do I keep the circulator pump on all the time on my heating boiler?

If I want to have the boiler pump on 24/7 while the L8148A is powered. Can the high/low limiter controller do that? - On 2022-03-03 by Paul Tesolin

Reply by Inspectapedia Com Moderator

@Paul Tesolin,

In Canada it's common practice for the circulator to run 24/7 all during the heating season.

In that set-up the circulator is wired-direct from an on-off switch, not from the aquastat, and ALL the aquastat does is turn on the boiler when the boiler temperature drops.

Question: I shorted some wires and now the aquastat doesn't work - do I need a new one?

Hi, I am a homeowner. My Utica boiler has L8148 aquastat.

I was changing the Taco circulator pump and I made a mistake while power is on and I caused a short with line going to taco pump.

Now the aquastat has stopped working after the electric short.

So do I have to replace the aquastat? - 2019/11/15 Anon2 said

Reply: Yes: Shorted wires in a Honeywell L8148 Aquastat & Similar = replacement needed

If you shorted the power wires to any heating control including the Honeywell L8148 Aquastat then it’s quite possible that the control has been damaged or destroyed and will need replacement.

L8148E Aquastat: circulator pump won't turn on

My boiler is controlled in part by a Honeywell L8148E. Everything seems to work except that intermittently the circulator pump does not run. During these times, if I press on the flap on the top of the circulator relay, the relay pulls in and the pump runs for the remainder of the call for heat.

In many spots on this page you indicate that the relay can be replaced. However, it is not clear if the relay simple unplugs from a socket or if the the whole L8148E must be disassembled so that one can un-solder the old relay and re-solder in the new relay.

Please clarify. Also, if you can provide a part number and/or supplier for the relay, I would be grateful. Thanks.

To be clear, this is a very old (at least 35year) L8148E. That appears to be the complete model number. I see no addition digits.

Also, what I called the circulation relay I note now your diagrams call the "Switching relay." - On 2023-02-02 by Tom T -

Reply by InspectApedia Publisher - circulator relay replacement is not simple repair

@Tom T,

Thank you for a helpful question about circulator relay replacement.

I should be more clear that while a relay can be replaced on a circuit board, typically that requires de-soldering the old and re-soldering the new relay, steps that very few heating service technicians are prepared and willing to perform.

Instead they'll typically replace the control itself.

Unfortunately it's not a simple plugin repair.

Before replacing the aquastat be sure to review

CIRCULATOR PUMP WON'T START

Followup by Tom T

@InspectApedia Publisher, Thanks for your quick reply. Since it seems I will have to disconnect and demount the whole L8148E, it seems I need to know more about the immersion bulb connection at the Aquastat sensor port.

During the demounting process, would I disconnect the immersion bulb from the Aquastat sensor port ( if so, how?) or, would I have to pull the other end out of the well on boiler and have a delicate, messy (covered in thermal grease) tail extending from the Aquastat?

If I disconnect the immersion bulb from the Aquastat sensor port, is there a risk of spilling the liquid that is inside the bulb? I know its a lot to ask, but pictures of the sensor port and/or solder side of the switching relay would be helpful.

Thanks again for any reply and for this great page (do you sell the parts in question?)

Reply by InspectApedia Publisher

@Tom T,

A quick search of InspectApedia using the on-page search box finds our article that addresses your thermal sensor and sensor well question in considerable detail:

AQUASTAT SENSOR PROBE HEAT CONDUCTING COMPOUND

illustrates the components at the boiler and explains about thermal grease.

In my OPINION on recent boilers there is not a shred of issue about glop, mess or stickiness of thermal-conductive grease. There was a gripe among technicians who said that they encountered, on much older boilers, thermal grease that hardened, making removal of the sensor from the well more difficult.

Keep in mind that there are two very different installation details for the thermal sensor for aquastats.

Some aquastats have the sensor mounted projecting right off of the back of the control that is in turn mounted right onto the boiler.

Other aquastats use a "remote" sensor whose sensor bulb is connected by a thin copper tube between the body of the aquastat and the sensor mounted in a well on the boiler (or as a strap-on sensor in some installations).

About buying parts from us, no.

We do not sell anything. No products, no services.

InspectAPedia.com provides building and environmental diagnostic and repair information.

In order to absolutely assure our readers that we write and report without bias we do not sell any products nor do we have any business or financial relationships that could create such conflicts of interest.

However aquastat controls are widely available from your local plumbing and heating suppliers as well as from online vendors. I recommend going to your local supplier as they can offer direct help and advice for your situation - if the vendor will talk to you at all.

Some local HVAC suppliers are reluctant to even sell parts to consumers as they don't want to offend their main customers: heating service companies and technicians.

Followup by Tom T.

@InspectApedia Publisher, Thanks. Yes I'm familiar with that diagram.

My question was about the connection inside the box, which isn't shown. Also, I was asking about buying the individual switching relay, not a complete Aquastat. I doubt any local HVAC suppler will sell me just a switching relay.

Anyway, I wanted to let you and your readers know about the bandaid I've come up with for my stubborn relay. I've taped a small piece of spongy foam to the flappy thing on top of the relay and placed the Aquastat cover back on the box.

I'm holding the lid in a position with some zip ties to apply just enough pressure to the top of the spongy foam so that when there's a Call for Heat the relay actuates.

Thanks again for everything.

Reply by InspectApedia Publisher - be nervous about forcing ANY electrical device to close

@Tom T.,

That's a clever if risky band-aid, Tom.

It sounds as if the spongy-band-aid is confirming that either the relay is losing its closing-strength or it has burned contact points. What you did "works" - and I recall when one of the astronauts aboard a space shuttle "fixed" their on-board computer by giving a good whack while the experts on the ground were still paralyzed in meetings arguing about what to do.

But I am a little nervous about forcing ANY electrical device to close - that there could be an overheat and electrical short or fire. So do keep a close eye on your sponge-bob repair of a bad aquastat relay.

To be candid, I found bad relays, I tested them by pushing them shut (as does your sponge) but i never replaced one on the circuit board, I just replaced the aquastat entirely.

If the relay itself is bad, you probably don't have to remove the thermal sensor signal end from the aquastat if you can de-solder off and re-solder in an equivalent relay.

If you proceed with this advanced Junior Engineering project, do take photos that we might share.

Thanks.

DF

Where do I get a C wire for my new Smart Thermostat if none came through the wall from the heater?

I am considering an upgrade to a Smart Thermostat designed for Hot Water Boilers.

My boiler is controlled by the L8148E model Aquastat which has a 2-wire control up to an old "not-so-smart" digital thermostat that runs on 2 AA batteries.

All of the smart thermostats require a C-wire. Since there is no terminal on the Aquastat labeled Common, How or where do I run the new wire from? - On 2020-11-07 by grnnatmu

Reply by (mod) -

Grn

Take a look at NEST THERMOSTAT INSTALLATION & WIRING https://inspectapedia.com/heat/Nest_Thermostat_Wiring.php

and you'll see several examples of smart thermostats that I've installed that needed only the two original R and W thermostat wires at the old room thermostat.

And at THERMOSTAT WIRE CONNECTIONS - https://inspectapedia.com/heat/Thermostat_Wiring_Instructions.php we cover how to wire up all types and brands of heating & cooling thermostats- how to wire up all types and brands of heating & cooling thermostats

such as THERMOSTAT WIRE CONNECTIONS - 2-WIRE like the T87F https://inspectapedia.com/heat/Thermostat_Wiring_Instructions.php#2w

To provide a C-wire for you new thermostat where none is found at your old wall thermostat, see the procedures we describe

at COMMON WIRE at THERMOSTATS

How to add a line voltage relay if using a 24VAC controller to turn on 120V equipment

I have a L8148E 1265 that i want to put on my boiler. The problem is i have a blower that needs to be 120v.

On the old control board L8148A the blower was wired to the B1 and B2 terminals witch on the L8148A is 120v but on the new control the B1 and B2 terminals are only 24v. How can i use this board to work and power my blower on?

I'll pay someone to help me figure out how to make this work On 2022-11-24 by corey

Reply by InspectApedia (Editor) -

@corey,

I think that if you want to use that new 24VAC version of the control you would need to add a line-voltage relay - as an additional control.

Then the Blower is run at 120VAC connected to the 120V side of the line voltage relay

and the relay is operated by the 24VAC circuit that is connected to the L8148E

An example would be to use the

Switching Relay w/ Internal Transformer DPST Line Voltage Relays
Brand:
Resideo
SKU:
R845A1030

Let us know if you need more help.

Of course you can always call your heating service company and ask for an experienced technician to install the relay for you.

Why is the B1 terminal different from the other screw terminals on the L8148 Aquastat?

Why is the B1 terminal different from the other screw terminals? On 2022-10-07 by Anonymous

Reply by InspectApedia-911 (mod) - B2 is a terminal intended to be connected to by a copper wire looped end, while B1 is intended to be connected to by a tab type connector that is in turn crimp-connected to the control wire.

@Anonymous,

Thank you that's a great question.

The difference between those two burner control terminals on the aquastat is that the B2 is a terminal intended to be connected to by a copper wire looped end, while B1 is intended to be connected to by a tab type connector that is in turn crimp-connected to the control wire.

Also take a look at the wiring diagrams in the instruction PDFs that we provide on this page and you will see how B1 and B2 terminals are used differently.

L8148 Aquastat Troubleshooting FAQs

Can I test a Honeywell 8148 Aquastat before installing it?

Is it possible to test a honeywell l8148a1017 aquastat ,to be sure it is in working condition, before you install it? - On 2022-04-18 by Rick Lambos

Reply by Inspectapedia Com Moderator - how can I test Honeywell Aquastat before installation? - No, bench testing is impractical: need the temp sensor working

@Rick Lambos,

That's a great question, thanks.

At AQUASTAT TROUBLESHOOTING

We list the standard aquastat test procedure steps,

but

I don't know of a complete BENCH-TEST procedure for a brand new aquastat - not one that could be completed on a typical test bench; you'd need to be able to expose the temperature sensing bulb to the range of temps expected at the boiler for a complete test.

Keep in mind that the aquastat is designed to respond to the temperature sensed by its sensor bulb that's mounted in a sensor well on the heating boiler.

So in theory you could immerse your sensor in water of a known temperature and then use a VOM or DMM to see that the aquastat turns on the circulator as expected.

But in my opinion it's both impractical and unnecessary.

I think the failure rate of brand new aquastats due to factory defects must be extremely small.

Buying a used control is always a pig in a poke, but there I would inspect the device for evidence of water leaks into the control, for corrosion, and for signs of overheating on the circuit board - visual inspection only.

What is causing my monitron electric boiler to overheat and produce steam

What is causing my monitron electric boiler to overheat and produce steam ? On 2022-11-09 by Don -

Reply by InspectApedia (Editor)

@Don,

Watch out: steam coming out of a hydronic type (hot water) heating boiler is dangerous, risking a boiler explosion (if the pressure relief valve fails) or scalding burns.

I would turn off the boiler and call for an emergency heat repair.

If the aquastat is properly set, then I suspect there's a poor contact between the thermal sensor and the surface of the sensor well on the boiler, or the sensor itself could be defective.

 

L8148G relay won't pull in

I have a L8148G board that the relay doesn't pull in on. I can only find L8148A,E, and J online. Can someone provide any info on the G version. On 2022-11-28 by K Carter -

Reply by InspectApedia (Editor) - replace the relay on an aquastat with a sister replacement

@K Carter,

Thank you for the question and photo - it led us to find some errors in our PDFs and in the article above

In sum, you'd use an L8148L to replace an (unavailable) L8148G. The difference?

The L8148G was not designed to support multiple circulator zones while the L8148L can support multi-circulator zones (but of course does not HAVE to)

We're still looking for an L8148G manual, though the G will be very similar to the other L8148 controls for which we provide manuals above on this page.

It's possible to replace the relay on an aquastat - it won't be unique to the L8148G - but considering the age of your control, few service technicians would make the attempt. I

Instead, I think a technician would replace your L8148G with one of its sister replacements

Primary circulator loses power when burner shuts off

I have an L8148A1017 and on a call for heat the burner and primary circulator come on.

When the aquastat senses desired temperature the burner shuts off and there is still a call for heat, but the primary circulator loses power.

What is causing this? I checked the amp draw on the circulator and it was around 2 and specs on the grundfos 3 speed pump says .7 amps is normal. - On 2022-11-17 by Steve S. -

Reply by InspectApedia (Editor) - replace failed aquastat relay or replace the aquastat

@Steve S.,

Let's start with a check of the wiring connections: it sounds to me as if your circulator may be miswired - OR- the relay on your aquastat is failing and the unit needs to be replaced.

Most techs would just replace the aquastat rather than attempting to repair the relay.

L8148B occasionally fails to work when the thermostat is calling for heat

I have a L8148B that occasionally fails to work when the thermostat is calling for heat. If I shut off power, by the power switch, the aquastat will work and will do so for a number of days and then stop working again. I power on and off and it starts working again.

Sometimes I need to turn the power on/off two or three times before the aquastat works and the boiler ignites. Any suggestions as to the problem? On 2022-06-27 by George B

Reply by (mod)

@George B,

Intermittent failures are hard to track down.

The next time your system won't heat, before turning power off, see if pressing on the relay in the control turns on the circulator.

Watch out: there's live voltage - watch what you touch, or don't go there if you're uncertain: you could be shocked or worse.

Other errors are a bad sensor or bad sensor contact or a failing control board or simply a loose wire. On 2022-06-27 by InspectApedia-911 (mod) -

L8148E 1265 Aquastat relay hangs up

Gas fired Olsen boiler has an L8148E 1265 aquastat controlling the igniter and circulating pump.

Twice this season the relay has hung up, the igniter does not engage but the pump does.

Can you identify this relay? I assume that it will be cheaper to switch out rather than replace the whole unit. On 2022-04-15 by Ken

Reply by Inspectapedia Com Moderator -

@Ken,

Right: There are OEM and generic replacement 24VAC relays like the one shown below, but most service techs prefer to replace thee entire aquastat control.

Honeywell 8148A Aquastat: circulators won't run when they should

Gentlemen,

I have the following setup:

Dunkirk XEB-5-HA5
Honeywell 8148A
2x Honeywell 40004850-001
Grundfos UPS15-58FRC

It is running two zones heat.

The thermostats are able to trigger heat in both zones resulting in the valves opening and the boiler firing up. The upper limit seems to consistently kick off at 180F and fire back up when temp gets low.

The circulator however will at best only run a bit while the boiler is running.

What are my options?

I'd like the circulator to run when one or both of the valves are open, but that doesn't seem to be the case...?

New Aquastat? Upgraded model?

Thank you, Rune On 2022-04-14

Reply by Inspectapedia Com Moderator - circulator not turning on when it should

@Rune,

If yours is a heating system in the US, then the usual way that it's wired is that the thermostat calls for heat and that opens the zone valve.

When the zone valve is in the fully open position, an end switch in the zone valve turns on the circulator.

Then the boiler temperature is what actually turns the burner on and off.

So if that's how your system is wired and the end switch is not turning on the zone valve there is a problem with the zone valve and switch, or the circulator relay, or the circulator wiring, or the circulator pump itself. That's something that are on site heating service technician can sort out with a few simple tests.

It makes sense to diagnose the problem accurately before we try adding on devices or switches or features that otherwise someone may think solve the problem that you describe.

Followup by Rune

@Inspectapedia Com Moderator,

It is a heating system in the US - Colorado. And it does just what you wrote. I have 123-4 V on the system. When the boiler is running it is getting power, however there is no voltage on the circulator.

I don't know how to check the end switch in the zone valve. Any guidance?

I truly appreciate this page and your reply - I'm a sucker for competence.

Thank you, Rune

Reply by Inspectapedia Com Moderator

@Rune,

OK so there may be a bad circulator relay - most techs will just replace the whole aquastat.

On 2022-04-14 by Rune

@Inspectapedia Com Moderator,

Thank you. What are the best options going forward?

-Buying a relay only?
-Buying the same 8148A and exchanging it?
-Upgrading it?

Thank you,

Rune

Reply by Inspectapedia Com Moderator

@Rune,

Few techs will replace the relay, though that's cheaper than a new control.

So you may need to replace the whole aquastat.

But before doing that,

and I say this with extreme nervousness because you're a stranger and I don't know how skilled you are and if you touch live electrical contacts you could be shocked or killed,

but all that said, sometimes I will simply press on the relay to see if that turns on the circulator.

That may tell that there is a bad relay.

And of course check for things that would be embarrassing to have missed like a loose or broken wire.

I check the circulator Itself by making sure that it will run when given direct power, but you already said that the aquastat was not sending power to the circulator.

Reply by Rune

@Inspectapedia Com Moderator,

I like how you think - and had already checked the relay with an insulated screwdriver. I can push it in, it'll kill the boiler and click right back on. After this I was able to intermittently read 70-80V or 117 V on the Circulator connectors (indicates a weak connection in the relay to my understanding).

The circulator is brand new and installed a few days ago. I am Macgyvering it to run via an external powersource while the valves are open to get heat dispersed in the house.

My trouble shooting (as newbie as it might be) actually started since I saw the boiler running and no circulator, so bought and installed a new circulator.

It seems like it would only run when the boiler was on which seemed wrong - why generate all that nice heat, turn off the boiler and then not distribute it around the house using the pump.

Should I upgrade to a better, newer Aquastat? Will they all allow the circulator to run while the valve(s) is open? Or do I need a more fancy version?

Thank you

Reply by Inspectapedia Com Moderator

@Rune,

You will see in this article series that there is a universal replacement aquastat but there's no reason not to replace with a new copy of the same one that you have.

See AQUASTAT L7224U UNIVERSAL OPERATION

 

Circulators won't come on until I hit the RESET button

My boiler system runs great, cuts on and off like it suppose to. Only problem is that a couple times a week first thing in the morning I have to hit reset so circulating pump will come on. runs great rest of day. It is a Honeywell Aquastat L8148A. Any suggestions ...thanks Greg - On 2022-02-14 by greg

Reply by Inspectapedia Com Moderator - use of reset button may need a call for service

@greg,

I'm a little confused about the aquastat RESET turning on the circulator pump, since usually when the aquastat turns off and requires a re-set there is a burner or flame or combustion problem - needing inspection, repair, or cleaning and adjustment by your heating service tech.

But if really what's turning on is the circulator, not the burner, when you RESET the aquastat, there could be a loose electrical connection or bad relay or bad transformer in the control.

I'd call for service before you lose heat more solidly.

Reader question: I force the furnace to run by using cardboard to keep a relay open.

My issue is that the relay only sends power to the igniter when it's in the open position.

Two days ago i lost heat, thought it was the circulatory pump but it wasn't. I replaced my Aquastat and still nothing. then when I was verifying my wiring, I opened the relay and the igniter kicked in.

It's 17 degrees today outside and 52 inside so I have a piece of cardboard keeping the relay open until it gets warm enough where I don't have to wear 5 layers of clothes in my house :)

Any thoughts on why this would be just the opposite?

I took some pics to help me explain it better. The picture shows my power coming in and then to my transformer, from there it goes to my Aquastat, the second picture.

The only way I can get the furnace to fire up is to keep the relay open with a piece of cardboard (marked with the red arrow in the second picture), then hit the burner button on my Blower. Once it's fired up everything works fine unless that cardboard is removed.

Thank you in advance for any suggestions or opinions you may have.

On 2022-01-17 by Mnorce

Reply by Inspectapedia Com Moderator

@Mnorce,

Watch out: NEVER force a heating control to "run" - doing so is dangerous, risking fire or other hazards.

if you are referring to C1 and C2 that looks dark, that's just a shadow.

You mentioned that what looks like a burn in the photo may be a shadow. Sorry it's pretty blurry.

If you are absolutely confident that your wiring connections are correct them it sounds as if the control has internal damage.

Change out an aquastat with a buzzing relay?

I have a customer who called with a loud buzzing noise coming from the relay in the L8148A1017. The circulator and burner are running normally. Do I need to change out the control? On 2022-01-10 by Mike

Reply by Danjoefriedman (mod) - Buzzing from the control relay means replace the aquastat

@Mike,

I would change out the control (as most techs are not about to go to the trouble and risk of replacing just the relay and its transformer on the circuit board)

I'd tell the customer that in our opinion it's better to replace the control now than to wait for the relay or its transformer to fail hard and leave them with no heat and maybe an emergency heat call.

Details are at

CHATTERING RELAY CONTROL SWITCHES

and

CHATTERING RELAYS, HVAC EQUIPMENT

and

HEATING SYSTEM BUZZING NOISE

L8148A sometimes makes a loud humming type sound.

My Aquastat L8148A sometimes makes a loud humming type sound. It appears to be coming from the switch relay. When I push the relay the noise stops.

The plumbing company wants to replace the White Rodgers zone valves with Honeywell zone valves.

They think that is the solution to the noise. The noise occurs when any of the 4 zone valves comes on. One of the zone valves is only a couple of months old. The Aquastat is only a couple months old also. On 2021-04-17 by Don Hardcastle -

Reply by (mod) -

@Don Hardcastle,

A buzzing aquastat is usually a failing relay or on occasion a failing low voltage transformer. That's disappointing on a new aquastat - so check for a bad transformer first.

See details about buzzing aquastats and relays and our suggestions at

AQUASTAT TROUBLESHOOTING https://inspectapedia.com/heat/Aquastat_Diagnosis_Repair.php

and at

HEATING SYSTEM BUZZING NOISE https://inspectapedia.com/heat/Heater-Buzzing-Noise.php

and don't hesitate to ask follow-up questions as needed;

please also keep me posted on your repair.

Also see WHITE RODGERS CONTROLS & MANUALS - all

Buzzing noise cured by replacing the aquastat

@Don Hardcastle, they replaced the Aquastat, even though it was new, and the noise seems to have disappeared. - On 2021-04-30 by Don Hardcastle

Reply by (mod) -

Don

Having replaced the aquastat and noting that the noise has stopped sounds reasonable and might well confirm our guess at a bad aquastat relay. Better to fix a problem like this before it fails hard and leaves your building with no heat in freezing weather.

While it's technically possible to do so, we will virtually never find a heating service tech trying to replace just the relay on the control board of a failed HVAC control; the time and trouble and risks just don't add up for the service company; it's quicker and easier to replace the whole control.

Installed a new aquastat, now we have no heat

Hi everyone,

I just installed a new AquatatL8418J on my boiler (along with a new expansion tank, pressure relieve valve nut and automatic pressure vent) and I can't get heat.

The boiler turns on, the water heats up but I can't get it to send out the water when the thermostats call for it.

I have 2 zones with separate thermostats and it isn't working for either so I am fairly sure it is not the thermostats or the zone valves causing the problem.

I labeled all my wires and rewired it based on the labels but I am wondering if I messed up.

I am thinking it is the T and TV connections that would be causing this particular issue but I don't know enough about it to be sure.

For fun both wires are red so its difficult to tell which is which and they both lead out to red wires on the zone valve motor boxes.

The relay doesn't engage when the thermostat is turned on, and if I manually press the relay the pump seems to come on so I think that rules out the pump as the issue either.

Side note, the replacement was technically L8148J1009 and my original one did not have 1009 on the model number but they looked exactly alike so I was guessing they updated the model number in the decades since the original was installed.
Thanks for any help you can give, its getting cold tonight :) On 2020-10-26 by Crystal -

Reply by (mod) - signs of overheated wires in Aquastat

Crystal:

Watch out: I see burned wires at the top of your controls, those two red wires

- I suspect there is a wiring error or a voltage error at this aquastat, and it's possible that the control has been damaged as a result.

Those wires are connected to what are supposed to be the Thermostat terminals, normally low-voltage 24VAC - so I think something's wrong here.

Who wired this up for you?

See the HONEYWELL L8148 AQUASTAT WIRING INSTRUCTIONS given as a PDF found above on this page.

Note by Crystal

I just wired it based on the one I removed. Same red wires with black spots on the one that had been running for years

Reply by (mod) -

OK still I'm concerned about those overheated wires; And there should not be more than 24VAC across those terminals.

Watch out: if you are not familiar with safe and proper electrical wiring you could get shocked or start a fire. - as I warn everyone.

90 VAC reading between B1 and B2 on the 8148 aquastat

Largely, my aquastat seems to be operating in accordance with what is described above, but for the fact that I get a 90 VAC reading between B1 and B2.

I have 117 VAC between L1 & L2, and interestingly enough that same 117 VAC between L2 (L2 as common) and B1 (boiler line output).

The conclusion is there is some voltage drop... having 90 VAC on the boiler supply output (B1/B2)

I assume is not enough to fire the boiler... not sure on that. Can anyone confirm? Any ideas what would be causing the voltage drop? On 2020-01-14 by Travis Z

Reply by (mod) -

Travis

I suspect the problem is in a connection or wire right on the aquastat control board or relay.

I'm assuming that you've checked or can check that
- the supply voltage to your building is around 120VAC at the same time that you are seeing 90VAC at the aquastat B1 B2 (burner) terminals

- there is no problem with under-sized wiring

- the circuit itself is not overloaded

- there are no obvious loose wiring connections

Hitting the side of the Aquastat or sometimes carefully pushing on areas of the board, would then cause the burner to fire.

First off, THANK YOU for this awesome website! It was very helpful in diagnosing an intermittent problem with my L8148 1090 Aquastat. The Aquastat was not always firing the burner correctly.

I'll describe it here, in case anyone in the future has a similar issue: It would initially fire correctly, but sometimes cut out at a mid-range temperature say 120F or so, or sometimes not re-fire after reaching the high-temp limit and then cooling past the normal low "limit".

Hitting the side of the box, or sometimes carefully pushing on areas of the board, would then cause the burner to fire. There are videos on YouTube stating that on these models, some solder joints on the backside might go bad. I believe that was the case with mine.

Replacing the Aquastat fixed the issue. I inspected the back of the board of the old one, and there were no obvious bad solders, but I'm still pretty confident that was the culprit. Thanks for this page. It gave me a much better understanding of the function and proper operation of the Aquastat. On 2020-01-01 by Fred-

On 2020-01-01 - by (mod)

Thank you for your generous words Fred and for the posting which will certainly help other readers.

L8148 Aquastat Model Choice FAQs

Which model number L8148 Do I need?

@Inspectapedia Com Moderator,

I am looking for an Aquastat relay with 24 volt on the burner circuit I don't need any damper control just straight-up 24 volt and 110 for the circulator does anyone know the model number for this - On 2022-01-20 by Anonymous

On 2022-01-20 by Inspectapedia Com Moderator -

@Anonymous,

Take a look in the L8148 manuals / instructions [PDF files] given on this page and you'll see the 24VAC rating for some models of the control - eg. in the table below excerpted from the L9148 instructions.

8148J Aquastat relay differential went from 20 degrees to 5 degrees over the years.

On my SB Smith boiler, my L8148J Aquastat relay differential went from 20 degrees to 5 degrees over the years. I read the low limit is not adjustable. Does that mean my probe or my relay is bad? High limit works fine at 180 degrees. Shuts off fine with temp. satisfied. Drops down with circ pumps running to 175 degrees and fires up the boiler again. Not 160 degrees.

Also after looking at the literature on your site for my Aquastat relay, how do I know what my factory differential setting is? I'll try to keep searching. Thanks - On 2021-10-19 by Chuck S L

Reply by inspectapedia.com.moderator -Factory differential settings on Aquastats

@Chuck S,

Factory setting is typically 180 for the HI and the LO will be set to at least 20 degrees below that, so 160 or less, and the DIF may be anywhere in this range.

You'll see those details in a thorough explanation in the article above on this page

It's true that there are some controls in which the low is fixed at 20 degrees below the high setting.

Keep in mind that this is not lab grade equipment and that the actual measured temperature may vary a bit from the setting on the control. It's also the case that the boiler gauge itself is not lab grade and it may not be precise either.

Why did Honeywell discontinue the L8148A1090 aquastat ?

why did Honeywell discontinue the L8148A1090 aquastat ? the cross reference is the L8148A1017 which is a "cold start" stat. On 2022-02-10 by Bruce -

Reply by Inspectapedia Com Moderator

@Bruce,

Fair question and I don't have an authoritative answer other than to trust the Honeywell engineers.

But I think that the company wanted to simplify the product line by making a more universal aquastat; that makes repair parts stocking at the local vendor easier too.

Check the L8148A1017 IO manual for wiring and switch opinions.

See AQUASTAT L7224U UNIVERSAL

Using the L8148 Aquastat with Other Devices & Thermostats

How to connect a WYZE C-wire for a thermostat connection to a honeywell aquastat L8148E box

how do i connect a wyze C-wire for a thermostat connection to a honeywell aquastat L8148E box? - On 2022-02-18 by jp -

Reply by Inspectapedia Com Moderator - how do i connect a wyze C-wire for a thermostat connection to a honeywell aquastat L8148E box?

@jp,

The C wire is Common or a voltage supply to the thermostat.

The aquastat terminals don't provide that wire. You'd need to obtain C from the thermostat's 24VAC power transformer.

Or you can plug in a local transformer and run a wire up to the thermostat directly - that's the simplest solution.

See details

at COMMON WIRE at THERMOSTATS

How to add a Honeywell HPZC105 to a boiler with an 8148E Aquastat

Hi. I'm trying to add a Honeywell HPZC105 to my boiler. But I can't find anything anywhere that discusses the connections between the controller and aquastat.

Can you point me in the right direction.

My aquastat is an L8148e and the valves are 4 wire 8043e's. Thanks. On 2021-09-20 by Mark

Reply by Inspectapedia Com Moderator - connections between boiler and aquastat

@Mark,

and other readers; if you don't already have the IO instructions in-hand, see

HONEYWELL HPZC105 ZONE CONTROLLER INSTALLATION MANUAL [PDF]

that has some simple wiring examples like one I'll show below.

If that's not enough, see the more-detailed help given in

HONEYWELL HPZ & HSR HYDRONIC PANEL WIRING DIAGRAMS [PDF]

from Residio Resideo Technologies, Inc.
1985 Douglas Drive North, Golden Valley, MN 55422
1-800-468-1502
33-00476—02 M.S. Rev. 02-20

Where do the thermostat wires connect to this control GuardDog RB-24 low water cut-off.

I get that but I just don't want to connect the lwco wires for 24vac power incorrectly (as you said, it might not matter). The attached image (if it's visible) should explain. Thanks again. - On 2019-11-28 by tightwoods -

Reply by (mod) - wiring 24VAC controls

Tight

At the control the two thermostat wires that reach that point are acting as an on-off switch.

So it doesn't matter which wire connects to which of the two T Terminals

Followup by tightwoods - I'm trying to use this as a power source for a GuardDog RB-24 low water cut-off.

The L8148A 24 VAC terminals are both labeled "T". Shouldn't one be Hot/Red and the other Common?

I ask because I'm trying to use this as a power source for a GuardDog RB-24 low water cut-off. It wants the red wire to go t 24 V+ and the white wire to Common. I don't want to fry it. Thanks.

Followup by tightwoods

Danjoe, the low voltage transformer that I would like to use is that which is built into the L8148A boiler aquastat which sends 24 VAC to the T-T terminals.

As you are aware, Honeywell doesn't label them R-W so I don't know how to tell which T is R and which is W, if it even matters since AC goes both ways.

Maybe I can't use the aquastat transformer because it seems that connecting the R & W lwco wires to T-T would, in effect, complete the circuit & trip the relay to run the boiler & circulator.

With a separate 24 VAC power supply, wiring the Normally Closed lwco switch yellow wires in series with the thermostat makes perfect sense. What do you think? Have a Happy Turkey day.

Reply by (mod) - wiring details: connecting the thermostat to the L8148

Thanks for the follow-up, Tight.

I think our confusion (mine perhaps) with your question is about just where we're obtaining the two thermostat wires.

at THERMOSTAT WIRING HONEYWELL

we describe a simple two-wire thermostat wiring hook-up

On a simple traditional thermostat such as the Honeywell T87 the Red wire is the lead coming to the thermostat from the heater.

IN THE THERMOSTAT this wire connects to the "R" terminal.

On that same thermostat the White wire coming to the thermostat from the heater connects to the W terminal IN THE THERMOSTAT.

The thermostat itself is simply operating as an on-off switch that, on a call for heat, joins R to W to turn on the heater.

Now

Let's back up to the low voltage transformer in, on, or near your heating equipment. At the transformer itself the R and W wires originate.

At LOW VOLTAGE TRANSFORMER TEST

we describe how one can use a VOM or DMM to identify which of those two R and W wires is which.

Perhaps that will help.

Reply by (mod) - low-voltage 24VAC wiring - no polarity on AC Low voltage transformers

Right its AC

AC Voltage has no "polarity" - so you can connect either wire to either side of the control.

Technical note: this is even true right at the low-voltage transformer. The high and low voltage sides within the transformer are isolated from one another. The low-voltage transformer used on heating and ventilating equipment and controls is an alternating-current or "AC" device.

Details are at LOW VOLTAGE BUILDING WIRING and at other links in our discussion, given below.

 

Need a Manual for Honeywell L8148G Aquastat

I have a Honeywell L8148G Aquastat Relay. This is a model "G". Is there a manual or any diagrams for this model? I can't find one. - On 2018-10-09 by Mal

Reply by (mod) - provided here

A HONEYWELL R8148G MANUAL [PDF] is here:

or use the CONTACT link at page top or bottom and I can email you that PDF

It's a big 5MB file so give it a moment to load before you try downloading it.

If your control is in fact an "L" 8184G please post here a photo of the control cover, label, and interior as photos that you can include using the "Add Image" button (one per comment) and I'll check further.

Followup by Mal

Apologies for my ignorance. I believe I have a L8148E Aquastat. The added zone relay is labeled Aquastat relay type L8148G. The covers were switched. Reading glasses and a good light helped.

I did find this schematic inside the cover.

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

Reply by (mod) -

Well that's certainly a HONEYWELL L8148G AQUASTAT MANUAL [PDF]

Indeed relay and control numbers form a sea of characters upon which anyone can easily lose one's bearing.

Clarifying, the L8148-series is a aquastat control, monitoring boiler temperature and controlling the burner. Hence the word "Aqua" (water) in the name.

Honeywell does produce zone switching relays such as the

Honeywell R8146 series such as the L8148J1009/U

The "U" in the name stands for "Universal" as this relay was designed to replace a long list of older 8148 models such as the

L8148B, L8148E, and L8148G

this link provides a control cross reference chart:

HONEYWELL CONTROLS CROSS REFERENCE CHART [PDF]

And this link

HONEYWELL TRADELINE PARTS CROSS REFERENCE GUIDE [PDF]

provides a huge 992 page list of Honeywell Tradeline controls cross-referenced with their replacements.

L8148 Aquastat Setting FAQs

What does the DIFF or "Differential" mean in a high-limit-only Aquastat?

What does the differential mean in this high-limit-only Aquastat? For example, how would the operation differ for the 8-degree differential version vs the 15-degree differential version? - On 2019-12-11 by Fred -

Reply by danjoefriedman (mod) - Honeywell Aquastat differential explained

Thank you for the question on clarifying the DIFF on the Honeywell R8148, Fred.

Over at the home page for this topic - AQUASTAT L8148 DIAGNOSIS & REPAIR

we give a link to two manuals for the R8148

HONEYWELL L8148A,E,J AQUASTAT® RELAY SERIES MANUAL (Controllers) [PDF] (2001) product data & installation, operation manual including L8148 wiring diagrams

On this model the Differential is hard-wired in the control, it's "Nonadjustable."

Only the high limit is adjustable.

So if the HIGH is set, for example, to 200F, then when the boiler temperature drops to 192 degF (on the 8-degree model) or drops to 185 degF (on the 15-degree differential model) the switch will allow the boiler to turn on.

HONEYWELL L8148A E J AQUASTAT RELAYS MANUAL [PDF] (2002)

Where is the lK2 Thermistor /Switch on the L8148E control

Where is the lK2 Thermistor /Switch on the L8148E control.

Is it part of the Bulb that goes into the boiler? On 2023-01-30 by Bill 186765 -

Reply by InspectApedia Publisher - Where is the lK2 Thermistor /Switch on the L8148E control

@Bill 186765,

The bulb that inserts into the sensor well in the boiler is a temperature sensor and copper tube that communicates to the control itself.

The immersion bulb attached to copper tubing that connects to a sensor port in the aquastat where it operates a switch.

Both bulb and tube are filled with a fill liquid that expands or contracts in response to temperature. (Just how well it does that depends on the quality of thermal contact in the sensor well - which is why the manufacturer wants you to use a thermal conductive paste).

As boiler temperature increases, pressure in the bulb and cap tube increase, causing the end of the cap tube in the aquastat to operate the actual temperature response switch.

There is some design variation in just how these temperature sensors work on various aquastats, but this excerpt from Honeywell is helpful:

Sensing element

The liquid filled sensing element, including well or sensor assembly, responds to temperature changes of water in a heating system.

The sensor element has a diaphragm type power head connected to a tube type capsule, through a small bore capillary.

Expansion of the liquid, which completely fills the sensing element, is the means of motion of the diaphragm.

If you can tell me where you read about a IK2 Thermistor/Switch on aquastats I'll be glad to study that further to get us both on the same page here.

Thanks

DF

See

AQUASTATS THERMOSTAT PRODUCT HANDBOOK [PDF] Resideo, retrieved 2023/01/31 original source: https://docs.rs-online.com/a61b/0900766b80691404.pdf

Thank you to our readers for their generous comments

On 2021-09-22 by Mark - link you sent I think fits my situation exactly.

@inspectapedia.com.moderator,

Thank you. I just finished up wiring the zones and valves. And the second link you sent I think fits my situation exactly.

Much appreciated. It's a drawing that comes from an addendum that I haven't seen.

On 2021-09-22 by Inspectapedia Com Moderator

@Mark, Thank you.

We've worked hard on this material for decades, so I'm really grateful when a reader finds it useful and trustworthy.

We also welcome your photos, questions, criticism or suggestions.

On 2020-01-01 by Fred

First off, THANK YOU for this awesome website! It was very helpful in diagnosing an intermittent problem with my L8148 1090 Aquastat.