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Honeywell L7224U1002 Universal AquastatHoneywell (Resideo) L7224U Aquastat FAQs
Q&A on the L7224U Controller Error Codes & Settings

Here we explain the Honeywell L7224U Universal Oil Heating Boiler Electronic Aquastat Controller

This updated Honeywell® combination control that sets boiler temperature and may also control hot water production via a tankless coil on the heating boiler. The photo above shows the interior of a Honeywell L7224U combination heating control, also called an "aquastat".

This aquastat model includes the "universal" term in its name because it can replace more than 40 older heating boiler controls. This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Honeywell (Resideo) L7224U Aquastat Control FAQs

Aquastat immersion well sensor details, adapted from Honeywell's L7224U universal aquastat installation instructions cited in this article series (C) InspectApedia 2015These questions and answers about the Honeywell L7224U Universal Aquastat controller installation and error code troubleshooting were posted originally at AQUASTAT L7224U UNIVERSAL - be sure to read that article.

On 2019-10-08 by (mod) - proper settings for HI LO HL or LL on this aquastat

Hi John

Keep the LL at least 20 degF below the HL

Our recommended aquastat settings are AQUASTAT HI LO DIFF SETTINGS

Also see AQUASTAT SETTINGS vs HEATING COST

On 2019-10-08 by John

if I have the HL set on just saying 200 how close should I set the temp. on LL to the temp. on HL

On 2018-11-20 by (mod) - my boiler keeps short cycling

A couple of things to look at.

One is whether or not you're using the tankless coil on this boiler. If you're not then you may want to disable the low limit.

Also sometimes the temperature sensor has not been properly installed in the well or is missing the heat conductive paste. That can cause improper temperature sensing.

On 2018-11-19 by del knauer

my boiler keeps short cycling I checked temp on aquastat in the morning when temp got to about 165 boiler kicked in ran to about 186 boiler kicked off I think my setting is 160 low 190 high.

that seemed ok, later in the day I noticed the heater firing for 5 to 10 secnds the shut down but the temp on the aquastat kept reading about 167 to 171 going on and off but sometimes would run normal

does this seem that the problem is the aquastat because not running to 187 190 high heat range. in the morning heater ran roughly 4 to 5 min but when it is short cycling 3 to 5 seconds

On 2018-10-22 1 by (mod) -

Wayne,

That maybe an 8 and an indication to check the B1 wiring

On 2018-10-21 by Wayne

I have 7224 aquaetat. Looks like a. BT error message. How can I fix this.? I'm alicensed plumber haven't worked with oil INAWHILE
At witts end

On 2018-10-20 by (mod) - err 3 = Hardware fault, replace the control.

Sorry to say, Joseph, that my data says

3=Hardware fault, replace the control.

I suppose it's possible to buy a defective control or to short it and damage it during installation.

You might want to give Honeywell tech support a call.

On 2018-10-20 by Joseph pichler

Shows err 3 no matter what. Even if I connect a different power source in a different building with all wires except line I and. 2 for power. It's brand new ?

On 2019-06-21 by (mod) -

Some aquastats including the Honeywell L7224U universal replacement have an anti-short cycle adjustment that you may need to visit.

Check that the temperature probe is properly seated and has thermal grease - as in my illustration.

On 2019-06-20 by Dean

Had defective Aquastat replaced with a Honeywell #L7224U on my cold start Pensotti boiler with a Rielio #40 burner.

Since then the furnace will heat for 4 minutes and shut down for 3 minutes and start up again, run for a couple of minutes, shut down again. After 20 to 30 minutes the cycle is repeated. Any ideas?

On 2018-10-20 by (mod) - 3=Hardware fault, replace the control.

Sorry to say, Joseph, that my data says

3=Hardware fault, replace the control.

I suppose it's possible to buy a defective control or to short it and damage it during installation.

You might want to give Honeywell tech support a call.

On 2018-10-20 by Joseph pichler

Shows err 3 no matter what. Even if I connect a different power source in a different building with all wires except line I and. 2 for power. It's brand new ?

On 2018-01-31 by (mod) - cold boiler, lights off

First confirm that your heating boiler has electrical power,

Next confirm that it has fuel

Then a really good place to start diagnosing and fixing a problem like this is to Use the on-page search box at the top or bottom of this page to find our diagnostic steps given at

NO HEAT - BOILER

On 2018-01-29 by John

bioler cold, thermostat calling for heat. network active LED not on

On 2018-01-08 by (mod) - i can't run my boiler from cold start as in having the LL off.

Ken

In standard U.S. wiring installations the thermostat turns on the circulator pump on a call for heat, and the temperature of the boiler water turns the boiler on and off as needed.

The LL on an aquastat is there to keep heat in the boiler where a tankless coil (for domestic hot water) is installed and in use.

Setting the LL too high can lock out the circulator - the control thinks you're making hot water with a coil and gives priority to the person in the shower.

I would look for a wiring error for the second floor thermostat.

On 2018-01-08 by Ken

i think i have discovered that i can't run my boiler from cold start as in having the LL off.

the second floor controller is just for the circulator pump and does not seem to turn on boiler. the lu7224u is for the first floor zone.

i use the fireplace a lot keeping the first floor temp satisfied so the boiler won't go on to heat second floor zone so it seems i have to have boiler HL and LL set so it is hot all the time so when second floor calls for heat, it will give heat thanks

On 2018-01-04 by (mod) -

Ken
The article above on this page describes using the I button on your LU7224U a quarter to display the HI, LO, and DIFF settings. Try checking those.

On 2018-01-03 2 by ken

i don't think anything is in conflict. when i set the LL back to lowest setting of 110, i do get heat

. i don't see a low diff setting. does not seem this is workin g from cold start if LL is off. this is a zone system too. my first floor zone rarely comes on since i have fireplace there. second floor need heat from the boiler which is controlled by the lu7224u. the first floor controller is an older dial type.

On 2017-12-31 by (mod) - Right HI LO DIFF settings on the LU7224U

Ken

Usually when we have the problem you describe it's because the control temperature limits have not been properly set -

See AQUASTAT L7224U UNIVERSAL DIAGNOSIS

see also AQUASTAT HI LO DIFF SETTINGS

Check that the Aquastat HI, HI-DIFF, LO, LO-DIFF settings are correct and not crossed or in conflict

and try those steps.

Let me know if that works for you.

On 2017-12-31 by Ken

Using the LU7224U. i recently installed a tank hot water heater for my domestic water. i read to turn LL off as i am not using the controller for domestic water any longer making my boiler work from a cold start when calling for heat. well, it is not working as such. when thermostat calls for heat, the boiler does not come on. is there another setting i need to adjust or change? thanks so much.

On 2017-11-09 by Al sweeney

Is there a suitable replacement for an r8182d control? Even if there are added separate relays to us is fine.

Example....I read it works similar but has no connection for cad cell , so one would need a seperate burner control to accommodate cad cell operation. Please advise! Thankx

On 2017-10-31 by (mod) - What would be an ideal high and low limit and diff for high and low.

DG

See AQUASTAT HI LO DIFF SETTINGS

Also check out AQUASTAT SETTINGS vs HEATING COST

On 2017-10-30 by DG

What would be an ideal high and low limit and diff for high and low. My system is set to HL 168 LL 150 with diff for high and low each being set to 10. But we noticed that the burner will many times be running at a temperature in the 190's and sometimes low 200's. Is that OK?

On 2017-05-18 by (mod) - which aquastat is right for my boiler?

Iva

To have space to give you a thorough and detailed answer I've replied at

AQUASTAT SELECTION GUIDE - please see that article

On 2017-05-18 by iva

HOW DO I KNOW IF THE AQUASTat controller is the right one for my oil burner furnance

On 2016-07-08 by (mod) - what are ZC and ZR

VR

ZC and ZR are zone control and zone request indicators, not settings.

Quoting from Honeywell

To read boiler settings, press the I key to read the parameter of interest. For example, press I and HL (High Limit) is displayed, followed by a three-digit number, i.e., 220, followed by °F or °C. Pressing the I button again will display the LL (Low Limit) followed by a three-digit number and the corresponding degree designator.

Adjusting Settings

To discourage unauthorized changing of Aquastat settings, a procedure to enter the ADJUSTMENT mode is required.

To enter the ADJUSTMENT mode, press the UP, DOWN, and I buttons (refer to Fig. 8) simultaneously for three seconds.

Press the I button until the feature requiring adjustment is displayed: ï HL_ ó High Limit. ï LL_ ó Low Limit. ï Ldf ó Low Limit Differential. ï Hdf ó High Limit Differential.

ï F - Có°F or °C.

Then press the UP and/or DOWN buttons to move the set point to the desired value.

After 60 seconds without any button inputs, the controller will automatically return to the RUN mode.

At AQUASTAT HI LO DIFF SETTINGS I suggest what I consider optimal settings for the HI LO and Diff.

On 2016-07-08 by vrosario63

Hello Dan, I installed a second heating zone on my boiler I have both pumps on the return. I am using the L7224U aquastat and the R845A zone relay.

My question is what should I set the ZR and ZC setting to on the L7224U aquastat? I have a wire going from the ZC terminal to terminal 1 on the zone relay and a wire going to terminal ZR to terminal 4 on the zone relay...

This is what the wiring diagram calls for but it does not mention what my setting should be.

On 2016-05-11 by (mod) -

VR

A tankless coil will almost always run out of hot water sooner than a typical separate hot water tank. Search InspectApedia.com for TANKLESS COIL to read details about this method of making domestic hot water.

The root problem is that the boiler is capable of raising water temperature (in the coil) by a fixed maximum number of degrees (max when boiler is at its hottest) and for a fixed maximum length of time (depending on the volume of hot water and / or latent heat in the boiler itself).

Consider that when heating a home the returning hot water heating zone water has given up a small amount of heat - the water leaves the boiler at say 180 and returns at 160F. But when making domestic hot water through the coil, the incoming water is entering at maybe 40 deg. F but trying to leave at 180F

. The lower incoming water temp in a tankless coil will always suck heat out of the boiler faster than the burner (designed for home heating not for making hot water) can put heat back into the boiler. You will run out of hot water.

There are things you can do to get the most of a tankless coil (like using a mixing valve and making the optimal aquastat settings); beyond that you'd need to modify the system such as dumping the tankless coil and going to an indirect-fired water heater.

In sum, a boiler rated for 4 GPM at the coil is not rated for 4 GPM indefinitely.

See HOT WATER QUANTITY IMPROVEMENT

See also

New Yorker CL BOILER Honeywell L7224/L7248 SUPPLEMENTAL INSTRUCTIONS [PDF] (2020)

On 2016-05-11 by vrosario63

Dan, here is my issue and why I am asking this. I install the L7224U on my New Yorker boiler. My settings are HL 180 with a 10 diff. my LL is 160 with a 25 diff. The aquastat is install in the front prob well of the boiler.

The boiler maintains the 180 and when she calls for heat she works as it should. My issue is that I run out of DHW. My shower heads are rated for 2.5 gallons a minute of flow. My boiler is rated for 4 gallons a minute of DHW but I still run out.

I closed my cold water supply to the DHW coil about 2/3 of the way and I am now able to maintain DHM without an issue.

The tankless coil also has a prob well, should I have install the aquastat at this point? I also noticed that they did not install a flow valve on the cold water supply to my coil. I just bought the house and there are a number of things I found on the boiler that were not properly done of which I have been correcting.

On 2016-01-22 by (mod) -

Nice going, and thank you for the feedback. The discussion will assist other readers.

Dan

On 2016-01-22 by Anonymous - signs of a defective L7224

Thank you Dan ! I believe you are spot on.I really think the L7224 was defective and it was the contact for the probe or within the control something was defective.

The Heating Company put a new L8148a on and the tech cleaned out the well that the probe went in.

The service manager said even though it was a different aquastat it would fall under warranty.(Hope they bite the bullet} He also said that with all the call backs they wouldn't charge an exorbitant fee. It works and since the old control went 16 years maybe it was a good choice to stick with . Thanks again!

On 2016-01-21 by (mod) -

John,

A lot of techs leave out the grease on the temperature sensor, claiming that it gets hard and causes later control swapout problems;

Honeywell says to use the grease. And the current grease doesn't petrify. I believe in following the manufacturer's instructions as they know their products and have a great interest in them working properly.

The fact that a control is working intermittently suggests a loose wire, bad sensor contact, or a control relay problem to me.

The newer control should swap in and work properly. I suspect either an installation error or a bad control.

On 2016-01-21 by Anonymous

Olympia cold start boiler with 1 zone and hot water.Simple setup but the labor even for the warrantied controls is costing me a fortune.

The Tech said they were looking into ordering the L8148-A that they took off last year which was working fine but talked me into replacing it because they said this newer control was the only one they needed to carry on the truck and it self diagnosed problems.

It is baffling how putting just a new probe on reset it to work for 24 hrs. Then after that I said just for the heck of it try the old probe again and it worked. Before he left he did put the newer one back on. now 30 hrs later out again with error 4 and neither probe will reset it.

On 2016-01-21 by John S - Error Code #8

Honeywell L7224U installed and replaced after a repeated error #8 3 months later new replacement error 4 The tech changed sensor and it worked then put the old sensor back on and it worked as well. 24 hrs now neither sensor will correct error 4

What the heck is going on.

When B1 is removed and sensor is running it still reads error 4. No voltage between B1 and B2 when off.Burner fires 2 second shuts off reads error 4. Tech suggest putting the old style aquastat back on. I mentioned putting grease in the well and he said it didn't matter. 10 degrees outside running out of wood .

On 2015-10-01 by Paul

Gentleman I'm getting an err code with what looks like an upside down F (err code). Can anyone help with this. Someone suggested the flame lens? Thank you

On 2015-03-11 by (mod) -

Anon

When I've seen this, and provided we have power and wiring is correct, it was either debris on contacts or a defective control.

On 2015-03-10 by Anonymous

the up & down buttons on my l7224u dont work iam a teck.

Question: I am sure my well sensor was bad not only from the condition of it but from error code 1 b

1 March 2015 Well sensor Resistance said:

I am sure my well sensor was bad not only from the condition of it but from error code 1 being displayed. Is there a resistance check that can be done throught the connector to determine this. I am sure the controller is smarter then me but I just want to confirm.

Symptoms included short cycling after lo limit was reached and of course error 1. I pulled out the well sensor and saw it was kinked abnormally. I bought a new sensor and mounted it in a new 3/4" deep well for better immersion and mounted the control directly on the well.

I have since ordered another well sensor so I can remount the control to it's original location on the boiler panel. At the time I did not realize there are optional sensor lenghts available for different mount locations.

Anyone have any resistance values for the sensors.

Reply:

I'm looking but haven't seen this test value.


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