Here we review where to find settings and how to adjust them on the Resideo (Honeywell) Universal Aquastat, the L7224U.

Honeywell L7224U Universal Aquastat Settings

Here we describe a reader's steps in troubleshooting the Resideo/Honeywell L7224U aquastat settings.

The L7224U1002 provides status and diagnostic information through an LED display to enhance the diagnostic process.

First, for a guide to the Honeywell L7224U diagnostic buttons, controls and LED readout codes,

see AAQUASTAT L7224U UNIVERSAL OPERATION & ERROR CODES

Then you may want to return to this page by using the "back" button in your browser.

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

In the FAQs of this article you'll read that several readers commented about great difficulty getting the Honeywell L7224U aquastat to run the boiler at a sufficiently high temperature and some reported that the HI and LO control functions seem reversed. We suspect that part of the trouble is in pressing buttons to get the right settings past the control's anti-tampering feature.

I include these L7224U adjustment procedure notes from the company's control quick guide linked-to in the citations just below.

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 simultaneously for three seconds.

Press the I button until the feature requiring adjustment is displayed:

• HL - High Limit
• LL - Low Limit
• Ldf - Low Limit Differential
• F - C - °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 control will automatically return to the READ mode.

[For systems that are not using a tankless coil]

To use the L7224U in a cold start boiler application, disable the Low Limit function by pressing the UP arrow button, DOWN arrow button and I buttons simultaneously for three seconds.
Then push the I button until LL is displayed. Then press the down arrow button until OFF is displayed. 

Trouble getting the Honeywell L7224U aquastat to behave - cool boiler, cool baseboards, or crossed controls settings

2 Feb 2015 Anonymous (Gregg) said:

I have a Burnham V14A-T boiler with tankless coil, aquastat is a (Honeywell L7224U1002). I'm not the brightest crayon in the box, but I am the owner/head technician/service engineer for a small CNC machine tool service center.

I usually get it right when it comes to figuring out how things are supposed to work, But I must admit, I'm a bit unsure about this.

I recently replaced the old mechanical aquastat on my boiler (about a week ago) it went up in smoke due to poor connections/corrosion in the push loc wire terminals. Any way I replaced it with the Honeywell L7224U1002 unit.

It works I have heat and hot water but not as I understand your explanation of operation, I have second and third guessed myself into a state of frustration, So hopefully you can shed some light on this situation

It seems as though the low limit has complete control over boiler temp. when t-stat is calling for heat. With lo limit at 140 it circulates 130-ish water through the radiators,(140-10 diff) burner running constantly circulator on at 140 off at 130 which is not hot enough to do any good. never gets close to the 210 hi limit.

If I set the lo diff to 25 as suggested to prevent circulator from turning on until 165 I get 115-ish water running through radiators(140-25 diff)It seems the diff is on the - side of lo limit.

The only way I can get hot water for heat is to set lo limit up to 190-10 diff then I get scalded every time I wash my hands, not so bad for me but the wife and grand kids have some unkind things to say about it.

If I reduce the lo limit to a safe level the house can't get up to temp. So what am I missing or is this the way its supposed to work?

The old one did pretty much the same thing, we just got used to it. But reading on this site left me with the impression that I did not need to have my boiler at 190 ALL the time,

And what you have written makes complete sense to me but that's not what I'm seeing here. 140 domestic 190 heat would be great, Can you help?

This discussion was posted originally

at AQUASTAT L7224U UNIVERSAL DIAGNOSIS

Reply: How to Set the Limits & Diff on the L7224U

Anon - dull crayon

Notes from a not so sharp pencil out of the box: I'm just thinking as typing here.

First you can read in the FAQs above that other fellows have had trouble getting this control to behave. I don't know but I suspect that at least part of the problem is that the Honeywell engineers included an anti-tampering feature on the control - to the joy of the HVAC service company - that can make button pushing and control setting sometimes not give you what you thought you set.

Have you taken a look at the quick guide

• HONEYWELL L7224U SERIES OIL ELECTRONIC AQUASTAT CONTROLLER [PDF] Technician's Quick Reference Guide

That simple guide gives step by step instructions for using the UP and / or DOWN buttons on the L7224U to move the set point to the desired value for

• HL - High Limit
• LL - Low Limit
• Ldf - Low Limit Differential
• F - C - for °F or °C

I would not set HI above 200F out of worry for pressing on the TP valve - that is running a bit hot and close to TP valve spill temperatures.

With LO at 140F the HI should be controlling on a call for heat and the LO and DIFF should be sleeping unless the boiler temp is down in the LO / DIFF range

SO I don't assume the control is not working and given that you're a smart Crayola I will for now assume you wired everything correctly and set the control correctly.

SO I ask - could there be another reason the boiler is simply not heating up to the higher temperatures: such as bad flame, or a thick coating of crud on the heat exchanger?

NO because you can foul up the control by crossing its settings - putting the LO up into the too-high range of 190 which then gives you a boiler so hot that the tankless coil is giving scalding water to the sinks. (serves you right)

Yeah it is acting as if the control is crossed somehow.

You could install a tempering valve at your tankless coil so as not to get scalded - that's a good idea in any event.

But I would try this

- turn off power to the control
- wait a minute
- turn power back on
- follow the instructions to set the HI LO DIFF to 200 140 25

I include this note from the PDF

Unlock the Anti-Tampering Lockout on the L7224U Aquastat

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 simultaneously for three seconds.

Watch out: if you keep getting locked out you may be waiting too long to press an up or down button to select the setting you want to change.

If after unlocking the control you do nothing else for 60 seconds or more, the control will automatically return to READ ONLY mode.

Press the I button until the feature requiring adjustment is displayed in this sequence:

HLo= High Limit.

LLo = Low Limit.

Ldf = Low Limit differential

F - C = °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
control will automatically return to the READ mode.

Settings on the L7224U if No Tankless Coil is Installed: "Cold Start" Boiler Set-up

To use the L7224U in a cold start boiler application, disable the Low Limit function by pressing the UP arrow button, DOWN arrow button and I buttons simultaneously for three seconds.

Then push the I button until LL is displayed.

Then press the down arrow button until OFF is displayed.

Reader follow-up: I can get past the anti tampering lockout

6 Feb 2015 Gregg said:

Thanks for the reply Dan, I have read all of the suggested material ad nauseum, Both Before and after installing the 7224. Before because I was having trouble with the old mechanical unit. This site actually led me to purchase the 7224.

I can get past the anti tampering lockout, as evident by the fact that I can raise and lower boiler temp by raising or lowering LO LIMIT and/or LO LIMIT DIFF.

I have verified that I can circulate 130 degree water, I can circulate 210 degree water, and a few temps in between. That is not the problem here. The problem is when calling for heat, the burner will run constantly until T-Stat is satisfied because the circulator turns on at the LO LIMIT (140)setting.

The circulator will run until Boiler Temp is down to 130 (at -10 diff) then the circulator stops, burner continues to run. round and round it goes,

Boiler temp. never gets above LO-LIMIT setting much less to HI LIMIT. If T-Stat is not calling for heat then burner runs until (140)LO-LIMIT is reached and everything stops until boiler cools down to 130, then starts again. Hi LIMIT is ignored completely. The way I understood it to work is the LO-LIMIT is ignored if there is a call for heat. Yes?

5 Feb 2015 Gregg said:
Thanks for the reply Dan,I just saw your response in FAQ's I will try cycling power and resetting values again

Reply: calling Honeywell for technical assistance with aquastats (maybe)

Let us know what happens, Gregg, and before tearing out any more hair consider you're part of a club of folks who've had trouble setting this control. If still you see no success I'd give Honeywell a call at their tech support line.

Watch out: The Honeywell company emphasizes that the control we are discussing should be installed, adjusted, or repaired by a trained HVAC service technician.

Telephone for Honeywell Technical Support with Aquastats or other Heating Controls
U.S. Toll-Free
1 (877) 841-2840
International
001 (480) 353-3020

Reader follow-up:

5 Feb 2015 Gregg said:

I'm way past pulling Hair, remember Kojak? Anyway, I cycled power and set values Twice-No Dice. same thing. I did however remove circulator lead while T-stat was calling for heat, the boiler temp rose to HI-LIMIT and shut off.

But when I reconnected circulator temp went to Hi-LIMIT -10 burner started, circulator kept running, boiler temp went down to 128 at that point I disconnected circulator again, it would have kept going down until whatever water temp was returning from house radiators.

My question is should circulator have stopped when HI-LIMIT -10 was reached then stayed off and restarted only after HI-LIMIT was again reached?

Current settings are HL=190, Hdf=10 LL=140 Ldf=25. Duu=OFF ASC=0 PC=OFF

Reply: how long should the circulator normally runb?

This may be a bit general but on a call for heat the circulator will normally run until either the thermostat is satisfied and the call for heat stops (and turns off the circulator) OR until the boiler temperature drops down into the range controlled by the LO and LO-DIFF (Ldf in your notes).

Reader follow-up: still confused about HI LO & Diff

6 Feb 2015 Gregg said:

Hi Dan, I messed around a little more last night, this unit would work (better) if the LO-LIMIT diff was on the upper side of LO-LIMIT but it definately is not.

I proved that to myself again last night. with LL set at 140 (diff 10)circulator will draw boiler temp down to 130 (Diff at 10) and down to 115 (diff at 25) On temp rise, burner still shuts off at 140. SO my settings now are HL 200 Hdf 10 LL 180 Ldf 10 Am I reading something into this that isn't there?

I'm sure I read that the LL diff of -10 is fixed and the adjustable up to 25 goes plus from LL MINUS 10 PLUS 25IN other words a LL of 140 and adjusted diff of 25 nets me 155 on temp rise before the ciculator is "ALLOWED" to turn on? Is this correct?

Reply:

Gregg

I don't know this control as well as I do the old R8182 series. On that control the 10 diff from the HI is hard-wired while the DIFF from the LO is adjustable as described in our article on that control. This L7224U has a programmable DIFF on the HI as well as the LO controls but we ought to re-read the documentation.

Have you considered giving your heating service company or Honeywell technical support a call?

Reader follow-up: trouble finding a heating tech to check the Honeywell L7224U aquastat

Gregg said:

I did call the honeywell tech line number that you provided, they refused to talk to me because I'm not a licensed contractor,

I called 2 licensed contractors that I know personally and they don't know anything about this control.

Reply: Excerpts from Troubleshooting Details for the Honeywell L7224U Aquastat

[Click to enlarge any image]

Troubling Gregg.

Working with Heating Suppliers & Manufacturers: Carol and Oil Burner Soot Visit JEM Supply

Have you asked your local heating service company to help with this problem and have you then asked if they'd call Honeywell to get help with the control? If they learn how to install and troubleshoot the control surely that'll be good for their own business.

Indeed often HVAC suppliers and manufacturers, recognizing that their principal customers are service companies and installers, are reluctant to talk with a homeowner as it infuriates their main customers.

When I first walked into a local HVAC supplier in NY, running my own heating service company with a partner, we had to hand over a business card and convince the supplier that we were "in the business" too (which we were) just to get the time of day.

Even then they were nervous, as there were other old-time customers sitting around (looking at the girlie calendars) and who were less than welcoming to a new competitor.

Over time, when the fellows saw we were serious (it helped to walk in through the back door and to arrive covered in soot and smelling of oil burners as well as to know the common names for controls and parts) our relationship blossomed and the supplier was very helpful.

In the 1980's I was working on oil fired heaters in partnership with a woman engineer who was very sharp. Carol S. had built her own car, solar panels, designed computers, and other stuff. And she was very straight and clean-talking (dinked was about the strongest language she'd use). I stepped carefully in demeanor and speech so as to avoid stepping in something. Carol was the boss.

So when she got particularly sooty while squeezing around a dirty oil fired boiler, and when two round black blobs of soot marked her coveralls, I didn't even think of saying a single word about it. Stay focused.

We walked into the service area of JEM supply in Poughkeepsie where about six old timers were sitting around jawing when they should have been out sucking the soot out of oil fired heaters. Silence fell instantly, rolling in not on cats feet but like a silent tsunami of fog. The old guys stared. Behind the counter you could have heard a pin drop.

Nobody said a thing. They all looked at me. They looked at Carol. They looked back at me.

Carol was the boss of our outfit and had more time in the field than I did, but obviously, and as soot blotches demonstrated, she was a woman. Those blots didn't compute easily for the fellows over at JEM supply. They looked at Carol again. They looked away.

They looked at me, expecting for me to speak as we walked up to the counter. It was a woman, but obviously we were working on heating systems: Carol was even sootier than I was. We both smelled bad. At least I did.

Carol stepped up to the JEM Supply counter and spoke in her own deep and confident voice.

"Gimme a Sunstrand J-pump 43A, left-hand rotation, with the internal bypass factory set, and a 23-A pump strainer"

Yes maam, said the JEM clerk in a too-loud voice. We took our parts and left. The tsunami of silence surely receded but not before we were driving our truck out of the lot.

See DINK FACTOR - Remember Carol S for another version of this report about our heating company. But don't call us for repairs.

OK so Check These Things on your L7224U Aquastat

Back to bidness: Am I right that you're not seeing any error code on the L7224 aquastat display?

• Who installed this display?
  
  Honeywell expects the control to be installed by a "trained, experienced service technician"
• Was its sensor installed 
  
  using the recommended heat conductor grease in the immersion well, and was the sensor tubing bent to assure good contact between the sensor bulb and the sensor well?
• After installation did the installer follow the product operation check 
  
  described in the installation instructions? (the link to that PDF is in the article above as well as at REFERENCES in our links to the original source at Honeywell Corp.)
• Is the HI Limit set within the range 
  
  given in the instructions? Typically from 130F to 240F
• Did you check that the control settings are not crossed 
  
  If the LO+Diff takes a control up into its HI+Diff range the circulator may not run when you think it should.
  
  Unlike the R8182D the HI on this control has an adjustable HI-DIFF setting (on the R8182D that's hard-wired at 10 deg). - have you re-checked that the HI DIFF doesn't overlap LO and LO-DIFF settings?

The LO range is between 110 and 120F (typically) but the company notes that IF this L7224U is being used to replace a Honeywell L8184A,C L7184A or L7284A,C then the LO Limit must be disabled - a step performed using the adjusting settings of the control (not by changing a jumper wire as is done on older aquastats).

The instructions describe how this disabling is performed (Press the UP and DOWN buttons at the same time for 3 seconds, then pus the I button until LL_ is displayed, then press the DOWN arrow until you see OFF)

• Stuck on anti-tampering? 
  
  Earlier I commented that some operators have had trouble getting past the anti-tampering step to set the adjustments correctly.
• Have you checked the voltage levels 
  
  being delivered to be sure voltage is in-range at 120VAC;
  Have you checked that the thermostat voltage is in range at 24V
• Finally, when the boiler is indeed firing and hot 
  
  but you're not getting the heat you want in the house, have you checked that the boiler temperature is above the LL setting?
• And if so, then have you confirmed that you're seeing 120VAC 
  
  on the control between ZC and L2? If you're not getting proper voltage there then the control is defective. If voltage there IS correct then the problem may not be in the control nor nor in its settings. In that case go back and re-check for a thermostat wiring error or zone valve malfunction or circulator or circulator relay or wiring snafu.

If you're still stuck we could see if Carol will come out of retirement and give us a hand.

Reader follow-up: Honeywell_L7224U_Aquastats setting details

(Feb 9, 2015) AUTHOR:Gregg (no email)

COMMENT:Hi Dan, I messed around a little more last night, this unit would work (better)if the LO-LIMIT diff was on the upper side of LO-LIMIT but it definately is not.

I proved that to myself again last night. with LL set at 140 (diff 10)circulator will draw boiler temp down to 130 (Diff at 10) and down to 115 (diff at 25) On temp rise, burner still shuts off at 140. SO my settings now are HL 200 Hdf 10 LL 180 Ldf 10

Am I reading something into this that isn't there? I'm sure I read that the LL diff of -10 is fixed and the adjustable up to 25 goes plus from LL MINUS 10 PLUS 25IN other words a LL of 140 and adj diff of 25 nets me 155 on temp rise before the ciculator is "ALLOWED" to turn on? Is this correct?

Reply:

Page 5 of the Aquastat instructions found at inspectapedia.com/heat/Honeywell_L7224U_Aquastats.pdf describe four operational states of the control and gives operating sequence and troubleshooting tips - on p. 5 and continuing.

As I read the company's drawing, for this aquastat the LO-DIFF is a temperature set *below* the LOW LIMIT. **IF** there is no call for heat, then if boiler temperature falls below the LOW LIMIT minus the LO-DIFF then the switch will "make" and the burner will turn on.

And **IF** there is still no call for heat, then the burner will remain on until the boiler temperature reaches the LOW-LIMIT setting.

IF there IS a call for heat the circulator will not run until boiler temperature has reached (or passed) the LOW-LIMIT setting. At that point the circulator will turn on. (The burner may happen to be on or off depending on what has preceded). P. 6 says that

on a call for heat the circulator starts when the water temperature is above the Low Limit setting (if applicable). Boiler temperature is checked. Burner starts when water temperature is below the HIGH LIMIT setting.

The burner will be turned off if

- the HIGH LIMIT is reached or exceeded

- the thermostat is satisfied (this will also turn off the circulator)

Question: can't set the controls on the Honeywell L7224U

(Nov 17, 2014) FRANK HOLLIS said:

Unit is now operating, and low and high limits are working, but I am not able to change the numbers using the push buttons. Can anyone help me? I contacted Honeywell to talk to a technician, but this can no longer be done probably due to legal issues. Sad!

Reply:

Frank the control has a "lockout to prevent tampering" that can make setting the control tricky.

Try the button pushing procedure shown in Honeywell's

• L7224U1002 Technicians Quick Reference Guide #69-1957 - handy summary of codes and functions

Question: not enough hot water from my L7224U Aquastat-Controlled Boiler

(Feb 18, 2012) MaineMark said:

I had an old controller go bad on an oil furnace & had it replaced with a Honeywell L7224U. Now our domestic hot water rarely runs hot during a shower. Any ideas or recommendations.

(Jan 16, 2013) VinceB said:

Same issue as MaineMark. If you read how the L7224 controller operates in the Honeywell manual, it is totally different than how the older controllers are described as working on your website.

Your website says that the L7224 operates the same (Hi limit, Lo limit, Diff) as, for example an L8124. I don't see it. Anybody have any suggestions?

(Feb 12, 2013) Lonmon said:
Same issue as MaineMark. I set the HI to 210 and the Lo to 190 according to the Burnham Boiler recommendations and it helped a little but it still runs cool and eventually you get cold water in the shower (it has a tankless DHW coil).

I left the Hi and Lo DIFF at the default at 10. Should the DIFF be changed on the Lo? Original control (L8124) called for DIFF of 25.

Same issue as MaineMark. I have a tankless hot water heater installed for DHW and a long shower will get COLD water at some point

I changed the Hi to 210 and the Lo to 190 in accordance with Burnham the boiler manufacturer recommendations and that helped a bit. They recommended a DIFF of 25 on my old L8124 controller. I left the Hi and Lo DIFF settings at the default of 10. Should i adjust the Lo Diff on this new L7224 controller to maintain better DHW heat?

(Nov 16, 2014) frank hollis said:
Limits are set, but the burner starts only when the low limit is reached, and stops when the upper end of the low limit is reached. The burner will not run to the upper limit.

Reply: Be sure your L7224U Anti Tampering is unlocked

Apologies Vince B.

I fixed broken html and added links to Honeywell's instructions for these two controls in the article above. Please take another look.

Frank

We are seeing several complaints and notes about confusion in the operation of this control.

Is the LO limit set above the HI or even close to it?

The LO needs to be 20 degrees below the HI or it will lock out the upper limit control on many aquastats.

A lot of readers have trouble setting the L7224U Aquastat, or think that they've set it but have not, because of its anti-tampering lockout that has to be released before you can actually change the control settings. I think this glitch is behind a lot of people's trouble with this aquastat.

 

...

Continue reading at HONEYWELL RESIDEO L7224U UNIVERSAL & L7248 AQUASTATS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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AQUASTAT L7224U UNLOCK & ADJUST SETTINGS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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