Questions & answers about heating boiler aquastat controls.

This article series explains how aquastats work and what the different aquastat controls are, what they do, and how they are set. We define the HI LO and DIFF controls on heating boiler aquastats and explains what they do and how they work. We explain the location and use of the heating boiler reset button found on aquastats.

Heating Boiler Aquastat & Primary Controller FAQs

The photo at page top shows a Honeywell R8182D combination heating control, also called an "aquastat".

On 2018-01-31 19:14:23.580074 by (mod) -

George, try the aquastat setting suggestions at

AQUASTAT HI LO DIFF SETTINGS

On 2018-12-22 by George

how to wire aquastat into relay transformer system with circulator

I have a Weil / McLain boiler with 2 zones using a what appears to be a 8182D Aquastat controller. I rewired things so that the thermostats control only the circulator on each zone respectively.

Since doing so the boiler seems to keep the temp at the low setting (140F) only and does not ever reach the hi setting of 180F.

What changes do I need to make so that the burner fires at 140 and turns off at 180?

On 2018-01-31 by (mod) - Typical Aquastat control cost

figure ballpark 250 to $300 for the control depending on the model, and an hour of service tech time which might be anywhere from 60 to $100

On 2018-01-29 by John weeks

What does it normally cost to replace one?

On 2018-01-06 22:44:51.044161 by (mod) -

At AQUASTAT L7224U UNIVERSAL https://inspectapedia.com/heat/Aquastat_Honeywell_L7224U.php

we discuss the settings for that control.

For other readers, on the Honeywell L7224, the HDF or High Limit Differential is a new feature:

High limit differential setting - (5-20 °F) (this is a new feature; above we said that this figure was fixed in the control)

and the LDF is the traditional low limit control

Low limit differential setting - (10-25 °F)

Setting the LDF to the highest number gives most hot water.

See https://inspectapedia.com/heat/Honeywell_L7224U_Aquastats.pdf

On 2018-01-06 20:31:49.728274 by Anthony185

I have a peerless burner WB-03, tankless hot water heater. I have a Honeywell L7224 Aquastat. Trying to get more (longer) hot water in

shower.

I am confused by all the posts explaining how to set "DIFF

My Aquastat has a HIGH DIFF & a LOW DIFF setting (HDF & LDF)

Which one, and or how should I set to try and increase my hot water in shower?

Current:

HL 200

LL 180

HDF 5

LDF 10

On 2018-01-06 17:36:18.565157 by (mod) -

Anon

In the suggested reading ARTICLE INDEX links see AQUASTAT HI LO DIFF SETTINGS for the recommende settings

On 2018-01-06 by Anonymous

I have an expansion tank an my aquastat is set at high 180 and low at 160 .

my question is what should the differential be set at, it is now set at 10. my aquastat is a Honeywell triple aquastat -relay type L8124A,C L8151A.

On 2018-01-01 by (mod) -

That sounds like a bad circulator relay or a bad aquastat. If the circulator runs I'd be inclined, in an emergency, to wire it to run continuously, disconnecting it from the aquastat until that can be diagnosed and repaired.

Then the thermostat will simply turn the burner on when the boiler temperature is low.

On 2018-01-01 00:29:36.747150 by edward

I have a weil mcclain oil fired boiler with a disabled domestice hot water coil, bolier is firing goes up to 180 as set. but the circulator is not coming on.

I hot wired circulator and circulator runs fine. I have 120 at L1 L2.

I have assorted voltage at C1 C2. C1 C2 Has been as low as 7 sometimes goes around 40 went up to 120 once for few seconds so I have disconnect circulator not to burn it out.

Thermostate has like 3 volts . transformer has 21 volts has been up to 27 volts( could just be my volt meter).

Is 11 dgrees out getting heat by convection or pluging circulator in for 20 min. I think is aquastat. should I bypass the low side( if so how) to further diagnosis aquasts

On 2017-12-18 by (mod) - Shorting thermostat wires might burn up a low voltage transformer,

Randy

Shorting thermostat wires might burn up a low voltage transformer, though it's not common.

The thermostat is basically an on-off switch, so you'd think that shorting the two TT wires together would be exactly the same as calling for heat continuously.

You might want to look at https://inspectapedia.com/heat/Thermostat_Diagnosis.php THERMOSTAT DIAGNOSTIC GUIDE

Then on a call for heat - setting the TT all the way up, see if the circulator is receiving voltage (Watch out you can be shocked and killed - if you don't know how to work on wiring safely get help from an electrician)

The Honeywell control you cite is, of course not the thermostat but an aquastat - described on this page at AQUASTAT R8182-SERIES CONTROL https://inspectapedia.com/heat/Aquastats.php

On 2017-12-18 by randy

tstat wires got crossed a couple of times before I could get them apart. furnace fired up a couple of times. fixed wires ,furnace runs fine but now wont circulate.it is a r8182 Honeywell .

On 2017-11-30 by (mod) - How to Check first for a loose wire or bad electrical connection.

Wayne,

Check first for a loose wire or bad electrical connection.

If clicking continues let's look more closely at what is clicking - probably a relay switch in the aquastat

. If so, check the connections to the circulator or burner that the aquastat is trying to operate. If those were working before, and apologizing that I am shooting from the hip, let's do these basic aquastat tests. If none of those sort this out I'm left suspecting a bad relay and thus a bad control.

Tell me the control brand and model and I'll check further.

How to Conduct Basic Boiler Aquastat Controller Tests:

1. Turn the wall thermostat all the way down so it is not calling for heat

2. Using a DMM or VOM assuming you know how to do this safely and are aware of shock hazards, else STOP here

else with great care not to get killed, check for line voltage (120VAC) at the power terminals to the aquastat (i.e. power is on) by finding 120VAc at the two Line-IN terminals, L1 and L3 are typical markings.

3. Check the low voltage transformer output: Check for 24VAC at the T and TV terminals - you will find 24VAC at one of these and 0 VAC at the other. If both terminals show 0 volts then the transformer is bad.

4. Now turn the Thermostat all the way UP so that it is calling for heat (remember to set it back down later). You should see 24VAC on BOTH of the thermostat or TT terminals inside the aquastat. If you don't then the thermostat is not calling for heat and most-likely you've got an open thermostat wire or a bad thermostat itself.

5. Now while still calling for heat, check that the aquastat is sending 120VAC voltage to the burner (the two B terminals B1 and B2) confirming that the aquastat is trying to turn on the burner (oil burner) or trying to open the gas valve if it's a gas boiler. This should be turning on the burner.

6. Now while still calling for heat, check that the aquastat is also sending voltage to the circulator pump - look for 120VAC at the C1 and C2 terminals. This should be turning on the circulator.

If voltage is everywhere it should be and a relay is clicking constantly OR a transformer is buzzing, those component(s) are probably bad.

Wayne: continue reading about aquastat diagnosis at AQUASTAT TROUBLESHOOTING https://inspectapedia.com/heat/Aquastat_Diagnosis_Repair.php

Jules: if your aquastat has the LO and DIFF enabled, those can be disabled. See the live link for AQUASTAT LO & DIFF DISABLED in the article links given at the end of the article on this page - just above.

On 2017-11-30 by wayne

Just install a new aquastat to my gas boier it continues to click.so turn it off.

On 2017-11-10 by jules

how do i stop the oil furnace from coming on to heat the house hot water

On 2017-04-12 by (mod) -

Joe

If the boiler starts immediately on a call for heat that's being driven by the actual boiler temperature, not simply the aquastat settings.
What you describe is correct in general, that is the thermostat (on U.S. typical setups) turns on the circulator and the boiler temperature is what turns on the burner.

But if on a call for heat the boiler temperature is already low the boiler may fire immediately.

On 2017-04-10 by Joe Fortuna

My oil fired boiler fires immediately when state calls gor heat. Aqua state is set 180 high, 140 low, 10 dif.

No matter what boiler temp. Is at. Circulator ok. I just seem to remember circulator running until boiler temp. Got to low, then fire.
,

On 2017-02-18 17:13:16.208061 by (mod) -

Al

What you describe doesn't sound right to me. There is no heating boiler aquastat whose LOW end is set so high as 220F.

Furthermore, it's the room thermostats that control room temperature. Start by checking the thermostat settings and compare those to room temperature.

If room temp goes above the set temp on the thermostat then a check valve or zone valve a the boiler may be stuck open.

On 2017-02-18 08:22:15.252833 by Al

my home heating system boiler was work fine until I had to replace the controller with Honeywell Aquastats .

now the house gets too hot .the radiators they become too hot .my old regulator was set at 180. However the Honeywell Aquastats the lowest range is 220F.how can fix this issue .thanks

On 2017-01-18 00:10:22.813968 by Joiry

Nevermind! I looked a little more closely at a single zone switching relay schematic and it instructs, in the tankless coil version, which terminals to use in conjunction with ZC and ZR on the triple aquastat.

I figure where there is a tankless coil, there is a low limit functionality, which is ultimately the thing that I am looking for. With low limit, I will be able to maintain a lower boiler temperature throughout the heating season except during the instances where there is a call for heat.

On 2017-01-17 23:22:54.986219 by Joiry I see line voltage t-stats controlling circulators on oil fired hydronic boilers all the time.

Hm really? I see line voltage t-stats controlling circulators on oil fired hydronic boilers all the time.

They have nothing to do with electric heat typically.

Maybe there are a lot of older houses in my area that may have new systems but still have clunky old 14 gauge control wires running through the walls attached to rotting, mercury t-stats barely hanging on to the plaster wall.

In any case, I'm more concerned with how to wire an additional zone to a triple aquastat. The triple aquastat schematics themselves seem simple enough. There are terminals for the burner, a circ and it's t-stat (low voltage), and a ZC ZR for additional zones.

That last part has me a bit puzzled. I assume I need a switching relay that has a ZC ZR on it in order to connect the second circ to the aquastats low limit functionality, but I have so far only found schematics online for 4 zone switching relays. One of those sounds a bit like overkill.

On 2017-01-16 15:16:32.797630 by (mod) -

Joiry,
With some care and engineering help it's likely that one could convert a 120V line voltage system such as line voltage thermostats to switch low voltage controls by using an appropriate relay switch.

But someone should call the Wise Lady from Philadelphia (Peterkin Papers, Lucretia P. Hale).

It sounds to me as if you are adding additional layers of cost and complexity (and thus unreliability) to an existing system that perhaps should be scrapped instead.

Watch out: usually where line voltage thermostats are installed they are controlling electric heat.

I don't understand how you've ended up with a mixed system that uses line voltage thermostats and an aquastat such as the R8182D with low voltage (24VAC) terminals (typically controlling a hydronic - hot water - heating boiler)

On 2017-01-15 by Joiry

Hi, I have a wiring/installation question regarding triple aquastats. I am interested in converting my Honeywell dual aquastat to a triple aquastat heat manger, perhaps the Hydrolevel Hydrostat or the like. I have a separate domestic hot water source.

The dual aquastat presently operates a two zone hydronic oil fired boiler running at 82% eff. Unfortunately both zones are controlled by simple line voltage thermostats.

After reading the schematics on triple aquastats, it seems apparent that low voltage wiring is necessary, especially for the heat manager to work properly. Is this true? Is there no way to operate a triple aquastat with two zone line voltage thermostat wiring?

It is possible for me to convert the thermostat wiring to low voltage fairly easily in the house as well as wire in a switching relay to allow the second zone to communicate with the triple aquastat. I'd appreciate any advice on whatever options will prevent the boiler from running to high limit 24hrs a day during the heating season.

I know that was a lot of questions. Thank you for your time!

...

Continue reading at AQUASTAT HI LO DIFF SETTINGS that explains the best settings to use & how & when to disable the LOW & DIFF controls or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AQUASTAT CONTROLS - home
  • AQUASTAT HI LO DIFF SETTINGS
  • AQUASTAT LO & DIFF DISABLED
  • AQUASTAT RESET BUTTON
• MANUALS for HEATING & A/C SYSTEM CONTROLS
• SINGLE FUNCTION LIMIT SWITCH
• WATER HEATER TEMPERATURE ADJUSTMENT CONTROLS

Suggested citation for this web page

AQUASTAT CONTROL FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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