Boiler Aquastat Control Setting FAQs

Index to all Aquastat HI LO & DIFF Setting Adjustment Q&A

Aquastat Settings vs Boiler Operating Problems - Setting Repair FAQs

Where do I find the aquastat & temperature/pressure gauge on my heating boiler & How do I Set the Aquastat?

How do we access the boiler temperature and pressure settings?

How do l get to the aquastat? Sorry, I know nothing about this

On 2023-01-05 by Anonymous

Reply by InspectApedia Publisher -

@Anonymous,

That gray box with red square in center (I've added a yellow arrow to your photo) is probably the aquastat; there may be a small screw at each end that needs to be loosened.

by InspectApedia Publisher

@Anon,

you don't set boiler pressure directly. The boiler pressure is set at 12 psi by the water feed/pressure reducer valve when it's set up. The boiler pressure gauge should read just under 30 psi at its hottest (under about 200F on the gauge)

The aquastat settings are given in the article I recommended.

see AQUASTAT HI LO DIFF SETTINGS

by Anon - Where is the pressure/temperature gauge on the boiler?

You had asked for a picture of the boiler settings as well but I don't know where the gauge is. I don't see it. Would it be behind another panel?

by InspectApedia Publisher - what does boiler pressure./temperature gauge look like

@Anon,

The boiler pressure./temperature gauge is a round dial with numbers on it - I think I see yours peeking out from under the aquastat (gray box)

See GAUGES, HYDRONIC BOILER

to understand what these look like and where they may be found

On 2023-01-05 by Anonymous

Here's a picture of the current aquastat, taken before the boiler came on for the morning, so it still shows temp at 70.

I do notice that the gauge says about 172 while the aquastat says 180.

And here's a close-up of the yellow block in the current aquastat.

I also noticed an old aquastat on the floor near the boiler and the yellow block in the upper right looks melted. Obviously that had been replaced at some point.

Hubby was able to help me this morning before work and the aquastat was at 70 and the thermostat showed temp at 66, the temp it's set to for morning (it was relatively warm yesterday and apparently overnight).

When the boiler first came on at the set morning time of 7:30, the house temp and thermostat were still set for 66, so I'm not sure why it came on at all. It ran for quite awhile and I took a picture of the gauge when the boiler turned off. The aquastat said 180.

I then turned the heat up to 68 to force the boiler to come on again and when it came on a couple minutes later, the aquastat said 168. It again shut off at 180 and the gauge picture was identical to the first I took.

I looked all around again and finally found the gauge below the grey box on the black part behins it. This is after not running for awhile because we set the heat lower for night. I'll try to catch a picture of it tomorrow as it shuts off.

by InspectApedia Publisher - what are reasonable aquastat settings

@Anon,

thanks for the photo - yes indeed, this (now abandoned) aquastat had a short or arc that ruined the control board - it's quite sooty.

I also saw evidence of overheating in your earlier photo of the aquastat circuit board - one side of the winding for a coil relay switch is yellow, the other burned brown.

Thanks - that's the low voltage transformer that converts 120VAC to 24VAC for use on the control board.

You can read about this aquastat and its settings at

HONEYWELL L7224U UNIVERSAL AQUASTAT

where we discuss the optimal settings for the L7224U control.

Please take a look and let me know if you have more questions.

How do I adjust aquastat to fix boiler short cycling?

I see you recommend 160 LO, 180 HI for Aquastat setting and you give some specific info [pay attention to the DIFF setting] for when there is a domestic hot water loop into a tankless coil.

Are there any changes you would make for a SuperStor which is on a regular Taco valve heating loop. Details are 2400 SF house, 4 zones, Beckett burner, Peerless WBV-03 112K BTU boiler, Taco SR506 switch relay.

I have had some short cycling problems this year and we are currently set to 140 lo, 180 hi. Heat is sufficient for the house (southern NH) and comes up quickly. On 2023-03-30 by Ken -

Reply by InspectApedia Editor (mod) - aquastat short cycling or "rapid-cycling" question.

@Ken,

If the boiler is short cycling let's first see which zones are calling for heat.

It could be that a circulator isn't running or not running properly so that for some heat calls the water in the boiler is heating up quite quickly.

Let me know which zones are active when you see short cycling.

by Ken

@InspectApedia Editor , So while I was away, my service tech installed a new Residio L7224/7248.

Since there are very few heating calls now, the only zone that calls for heat is the SuperStor 40. Boiler temp was reading 179 when I last visited.

Short cycling seems to have stopped but I will write back next winter when we actually have some need for heat! Thank you!

by InspectApedia Editor (mod) - aquastat short cycling or "rapid-cycling" fixed by new aquastat

@Ken

Thank you for following-up with us on this aquastat short cycling or "rapid-cycling" question.

It's possible that the prior unit had a defective sensor but in any case your post will help other readers.

Do let us know how the replacement Residio L7224/7248 aquastat is working at your next heating season.

Daniel

Aquastat Settings for Hot Water Quanity FAQs

What should be the DIFF (Differential) settings on my Honeywell triple aquastat -relay type L8124A,C L8151A.

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

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 2018-01-06 by Anonymous

by (mod) -

Anon

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

There, in the article section titled BEST DIFF SETTING - to get the most hot water - you'll see that setting the DIFF to a low number (10 is ok) may give you more hot water by turning the boiler's burner on sooner when you're using hot water.

How to set the DIFF control on myAquastat to get more time in the shower

In the section on keeping the tankless heater hot, don't you mean turn the the Diff control to a higher setting and set the lo control to the lowest settng (120)?

This would increase the on time for the boiler, making the water hotter, thus using less hot water during a shower, and allowing longer shower times. (Sept 2, 2011) Joe P.

Reply:

Joe, in AQUASTAT HI LO DIFF SETTINGS in discussing the DIFF setting, we stated:

Where a tankless coil is installed on a heating boiler to make domestic hot water (for washing and bathing) we prefer to set the differential (DIFF) to its highest number (usually 25 degrees).

But if you want the most hot water, you'll want to set the LO up as high as you can to keep the boiler hotter for making more and hotter water (storing more heat in the boiler).

The highest you can set the LO is to 20 degrees BELOW the HI setting (to avoid circulator lockout).

If you set the LOW DOWN instead of UP then when you are not calling for heat the boiler will be kept at a comparably lower temperature and you'll have less hot water than otherwise.

Thanks for the question, I'll review our text again and adjust it for clarity as needed.

How do I get more hot water from my boiler with a Honeywell L7224 Aquastat?

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 by Anthony185

Reply 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 the manual for your aquastat at AQUASTAT L7224U UNLOCK & ADJUST SETTINGS

See detailed help for getting more hot water beginning at HOT WATER QUANTITY IMPROVEMENT 

HI 180 LO 170 DIFF 10 - Our hot water supply is intermittent

Hello I need some help / advice,
I have a pearless boiler with a Honeywell L7224 Electronic Aquastat in the basement

HL is set to 180

LL is set to 170

and LDF is set to 10

On the 2nd floor we have 2 full bathrooms, when we take a short or try to fill the tub, its hot at first then it cools off, to a luke warm (on the cold side) after 3-5 minutes, then will get hot again after another 5 minutes. sometimes this cycle repeats, taking a hot bath is almost impossible, because you start filling the tub with hotwater and it mixes in the colder luke warm water shortly after.

I feel like I don't have the most ideal settings for my aquastat. can anyone familiar with this maybe point me in the right direction, On 2017-11-02 by Kyle

Reply by (mod) - Your aquastat is set incorrectly.

Kyle,

Your aquastat is set incorrectly.

Take a look at the recommended settings in AQUASTAT HI LO DIFF SETTINGS and use those. Then make this final adjustment:

in order to get the most hot water from your system that uses a tankless coil in side of your heating boiler you will want to set the differential or DIFF dial to its highest number which on most aquastats is 25 degrees

We run out of hot water at one bathroom

We have a boiler system with 4 heating zones. The water in the master bedroom shower (second floor, furthest from the boiler) never seemed to stay hot for very long.

I've set the aquastat settings in accordance with this article and it didn't seem to make any difference.

(I also adjusted the temperature setting in the Grohe shower valve.) I then noticed that if I crank up the heat in all 4 zones about a half hour prior to a shower, the hot water is fine.

Is there some other setting/valve/part I should be looking at?

(As a side note, the shower in the spare bedroom usually has sufficient hot water.) *shaking head* Thanks On 2023-03-08 by rob -

Reply by InspectApedia Editor (mod) - not enough hot water

@rob,

First, this discussion presumes that your domestic hot water for washing and bathing is being made by a tankless coil on a heating boiler.

If some building areas have adequate hot water and others do not, then the problem is not coming from the hot water source itself, it's a different problem such as:

- the effect of an anti-scald valve or temperature setting at the fixture (like your Grohe shower valve)

- the effect of longer runs of un-insulated hot water piping between the hot water source and the fixture

When you take steps to make the boiler as hot as possible, it's got more heat to send into the tankless coil that's making hot water to be delivered to fixtures - thus surviving effects like the ones we just cited.

See details at:

TANKLESS COILS

where you will find a series of articles about how to get the most hot water out of a tankless coil system.

Also read our explanation of the LO and DIFF settings above as those (along with any anti-scald devices on the sysetm) determine the hot water supply settings for a tankless coil system.

How much higher can I safely go on these aquastat settings to get more hot water?

Have 2 bathrooms, one shower gets enough hot water, other one begins to get cold after about 5 minutes. I've already raised the HI to 200 and LO is set at 180 on the aquastat, how much higher can I safely go on these settings? All the pipes are insulated in the basement. Thanks for your help. (Jan 16, 2013) John B

Reply:

You can't set the aquastat HI over 200 F without risking spilling the TP relief valve. You will want to take a look at other measures for improving hot water quantity such as flow restriction or going to an indirect fired water heater.

See HOT WATER QUANTITY IMPROVEMENT

Anti-Scald Mixing valve settings vs Aquastat settings vs Hot Water Temperature

My mixing valve was recently leaking so I had a buddy of mine replace it I have a two story home good hot water downstairs but upstairs water not as hot mixing valve is opened all the way up instead of in between and I have

The settings in the box are set at 1:60 low 180 I The settings in the box are set at 160 low 180 I did The differential is set at 20 Do you have any suggestions for me On 2019-01-14 by Ray Ingram -

Reply by (mod) -

I like the DIFF set to 25. You can also put the HI up as high as 200 (no higher or the TPR valve will spill)

But diagnostic questions might include

- was the upstairs water hotter before the new mixing valve was installed?

- has hot water pressure (actually flow rate) changed?

- is your water supply hard - high in mineral content ?

In the ARTICLE INDEX found near the end of the article

AQUASTAT HI LO DIFF SETTINGS you'll find several articles on TANKLESS HOT WATER COILS and their limitations as well as articles on how to increase the amount of hot water available.

Shower hot water goes cold after on eminute

Controlling a Peerless wbv-03 oil boiler with hydrostat and beckett burner Richie said:

Hey guys just had some questions.

I purchased a new house with a Peerless WBV-03 oil boiler with hydrostat and Beckett burner no water heater.

When we moved in we noticed hot water in shower would last 1 min and then go to cold.

After adjusting the cartridge in single handle hot water came out more but died in 2 mins now.

After reviewing this site and adjusting the hydrostat from 150lo/180hi to 180lo/200hi 25diff on both his and lo we are now able to take 7-8 min showers before the water goes warm.

Now I noticed that hot water pressure in the house is very low.

If I take a shower the hot water in the house fades drastically if someone opens a faucet but cold water is strong.

What could be my issue?

Also if I take a shower the only way to get hot water is to turn my handle all the way to hot position anything below that water is cold. Any suggestions (Dec 26, 2015)

Reply:

Richie

You made your boiler hotter which will give more heat to the tankless coil in the boiler, but if the tankless coil is clogging or clogged that will reduce the hot water pressure or flow rate - though not the total quantity of hot water.

Double check the boiler temperature and see if the home is heating while you're showering.

Richie said:

We do leave our Honeywell heat on. Should I be turning the heat off in the house before I shower?

The hydrostat heats up when I shower but I do noticed that the gauge on boiler and hydrostat do not match if the exampl.

Hydrostat says 203 but boiler at about 195. It's always about 7-10off. Now by hydrostat does havery 30 diff as max. Should be setting it up that high or is 25 diff fine?

Reply:

The equipment is not lab grade precise, and measurement locations also nay vary.

You should not need to turn off heat.

See our detailed help at HEATING SYSTEM NOISE DIAGNOSIS 

How to fix cycling hot water temperature that drops too low

I have a oil fired HWBB with an internal hot water coil.

The low is at 160, the high is at 180, the diff is at 10. When we shower, the hot water takes a reasonable amount of time to get to the shower, but after 30 secs or so, the water goes to room temperature, stays there for another 30 secs, then gets hot again and stays there. Any ideas? (Mar 30, 2014) Anonymous

Reply:

Interesting; I'm not sure what's happening. On a call for hot water it's the LO and DIFF that are in control. Set the DIFF to its maximum and you should get better performance. Let us know what that does to your system.

Comment by Anonymous

Sounds more like the water in the pipes are in a warm area then a cold area and then finally the hot water gets to your shower

Pipes carry a lot of water and if you have an efficient shower head (recommended always) then it can take some time to get to the hot water from the heater especially if they are the old pipes and your shower is a ways (by pipe not necessarily actual distance to furnace)..

You may want to trace the pipes from the shower to the furnace and see where it goes.. through walls which are on the outside of house vs inside, higher lower, etc and even turn the shower on as you hold the pipe at various places to see if what I say is true.

Sometimes it is the simple obvious reason in this case just physical having noting to do with furnace, which is why some people are getting instant heaters from Europe and installing them.

Speaking of which when i was in Germany the coolest thing I saw was a stainless steal multi tubed towel rack which had the the hot water going through it in the bathroom to dry towels and cloths..

very effective and space saving in small bathrooms with toilet tanks in the wall and use half of what we do per flush and have two flushes, small flush for pee and full tank for solids.... why not [in the U.S.] ? (Oct 17, 2014)