Heating Boiler Gauges

Types, location, uses & how to read the temperature & pressure gauge on a hydronic (hot water) boiler

Boiler Gauge vs Boiler Temperature Settings FAQs

I can't find the boiler temperature control on my Sentry Slant/FIn Boiler S-120 DP

I can't find where the furnace temperature control is. The temperature is 210* I want to lower it to around 180* its an older Sentry Slant /fin model number S-120 DP ?

Any advice would be appreciated. Thank you On 2020-12-12 by Mark

by (mod) - Here is where you set your boiler temperatures

Mark:

The aquastat that controls temperatures on a typical Sentry Slant/Fin S-120, like the model we show below, is the gray box shown at upper right in the image (Yellow Arrow in my image).

Watch out: 210 deg F is too high and risks spilling at the temperature-relief valve: a condition that can make the boiler unsafe.

See AQUASTAT HI LO DIFF SETTINGS

Crown boiler gauge 30 PSI reading seems high

It seems like the temperature on my Crown boiler is ok, but the PSI seems high. We only have our thermostat set to 66 degrees and the house is cold. Is there something we can do to help decrease the psi? Do we need to call a repair person? - On 2022-12-26 by Vanessa

by InspectApedia Publisher -

@Vanessa,

Your pressure gauge is sitting right at 30 psi.

1. IF you do NOT see spilling at the temperature-relief valve then that's good news - this isn't an emergency.

2. IF you took that photo when the boiler was up to full operating temperature, then that's "normal" pressure - considering that these gauges are not precise - not lab-grade instruments.

You can gently TAP on the pressure/temperature gauge - gently, as we don't want to break it - and see if the needles move.

3. Normal boiler pressures for a residential hot water heating boiler in a typical 2-story home are

- 12 psi when the boiler is cold

- just under 30 psi when the boiler is at its hottest

Check the HI setting on the boiler aquastat - it should be set to 200 degF or a bit lower - often a tech will leave it at 180F.

Details are at

AQUASTAT HI LO DIFF SETTINGS

Watch out: but if you DO see spilling at the temperature-pressure relief valve then the system is unsafe and should be turned off immediately; then call for repair service.

Let me know if you've got another concern like leaks at the temperature/pressure relief valve.

My Kool-Base boiler won't turn on at 12 psi and cold temperature.

Good morning, I have an old Kool-Base hot water boiler that is reading 12psi cold, and no temperature at all.

Pilot like is lit, thermostat is on 85 degrees, and can not get furnace to kick on.

It is so old, I'm not even sure I can locate the ignitor?

Is it right next to the pilot light? On 2021-11-02 by Jerry H

by (mod) - diagnostic suggestions

@Jerry H,

If it's an old boiler it may use a standing pilot that is normally always lit and not an igniter.

If you can't keep the pilot light lit, the problem may be a bad thermocouple.

See THERMOCOUPLE REPAIR / REPLACEMENT

If the pilot light is on and your thermostat calls for heat, then the boiler's gas valve should open and the burner ignite.

See the diagnostic steps starting at

DIAGNOSE & FIX HEATING PROBLEMS-BOILER

Is 24 psi at 174 degrees is normal in my heating boiler

My "typical" 2-story residential home's hydronic boiler system (Weil McLain, 10 years old) is at a 12 psi resting state when cold (good), and as the boiler runs and the temperature goes up so does the pressure in these increments: 21 psi at 160 degrees, 23 psi at 170 degrees, 24 psi at 175 degrees.

Is that ok? This is after I replaced the expansion tank this morning. This is better than it was.

Prior to my replacing the expansion tank this morning, the psi had been increasing at a faster rate (and nearly reaching 30 psi).

E.g. 25 psi at 160 degrees, and around 28-29 psi at 170-175 degrees at which point I shut boiler off because I did not want to exceed 30 psi and blow the relief valve.

Also, importantly, I believe I have RULED OUT the possibility of a leaky combination "pressure reducing valve/backflow preventer" because in an earlier test when I turned off the water line completely that feeds the autofill/backflow (ie. zero water could be added) I STILL had that faster pressure increased I'd just mentioned.

At this point, I'm hoping I'm OK with the first incremental changes in pressure I mentioned at the beginning of this post.

Does it sound OK or normal, or should I be able to get up to 180 degrees but only be at 20-22psi? I want to know if 24psi for 174 degrees is normal.

Finally, I am not sure if my boiler would shut off at 180 degrees on its own, or some higher number. I don't know what else could cause higher-than-ideal psi in my system at the temperatures I've mentioned. Any thoughts would be hugely appreciated. On 2022-02-28 by MikeB

by Inspectapedia Com Moderator - failed expansion tank can cause abnormally high pressures

@MikeB,

As long as the pressure is under 30 psi - 28psi is typical - when the boiler is at its highest temperature (somewhere below 200 degF) your residential hydronic boiler system is working normally.

I agree that a failed expansion tank can cause abnormally high pressures and once you exceed 30 psi, the relief valve should spill

Please take a look at

AQUASTAT HI LO DIFF SETTINGS

by Mike

@Inspectapedia Com Moderator,

Thanks! I will definitely read that aquastat page you recommended. I know nothing about aquastat so it will probably take me some time to research and understand it.

I will read about it and try to figure out how it might apply in my situation. I appreciate the help.

by Inspectapedia Com Moderator

@Mike

Glad to assist - keep me posted and ask for more help if needed after you read that PDF file. In the Article Index, you'll find extensive information about aquastats, what they are, how they work, etc.

How do I get the Temperature Down in my Weil-McLain boiler ?

No power (turned off) to the boiler but the circulating pump is 218 degrees too hot to remove safely and replace.

It has been off for 10 hours and is not cooling down. How do I get the temp down? Weil-mclain boiler Bell&Gossett circulator pump model nsf-22 On 2022-12-30 by cheryl

by InspectApedia Publisher - you've missed a switch or thermostat somewhere

@cheryl,

That sounds as if the circulator is continuing to run and I suspect that you have not turned off your boiler either.

Be sure to turn off power to the whole heating system, boiler and the circulator. Then your home and the heating zone will cool down.

by Vanessa

@InspectApedia Publisher, Thank you so much for your help!!

Boiler Gauge Replacement FAQs

What's the cost of a residential heating boiler gauge & what does the service tech do & charge-for?

What is the cost of replacing one of these gauges, the pseg guy came to check mine out and said the seal was broken, as in there was water in the gauge you couldn't read the numbers. then quoted and absurd amount, any ball park figures for the coast of parts? On 2020-11-01 by ss

by (mod) - $30-$40 for the gauge + labor: Here are the 12 steps in boiler gauge replacement

Thanks for a helpful question, SS: Typical cost of a residential heating boiler gauge;

A typical boiler gauge is about $30. to $40. U.S.

But it's helpful to understand what's needed to replace the gauge - let me outline it:

1. Drive to the site - travel time, in my truck stocked with repair and replacement costs - an overhead to the heating company

2. Talk to the customer to explain what's coming, then turn off the heating boiler and wait .... and wait ... for the boiler to cool down enough to work on it safely

3. When the boiler is cool enough to touch (water's just warm, not hot or scalding) bring in your drain hose, connect to the boiler drain, open the boiler drain, drain to an acceptable disposal point

4. Close the boiler drain, remove the drain hose.

5. With pressure off the system and boiler drained down at least to below the gauge mounting port, remove the old gauge

6. Clean up the boiler tapping, then prep the new gauge with a bit of teflon tape or equivalent, and screw it in

7 Re-fill the boiler

8. Turn heat on

9. Inspect the boiler for leaks including at the boiler drain. It's an ugly truth but too often a drain that's not touched for years, when used, spits out a dried-out stop valve washer and then can't be shut off. If the tech finds this she's got to be prepared to drain the system again and replace or repair the drain valve.

10. Purge the excess air from the system - this can take some time depending on what isolation valves were present, used, functional,

11. With boiler up to temp, inspect for leaks and

12. Confirm that every heating zone is working - don't leave the customer with an air-bound heating zone or there'll be an upset customer and a call-back for more work

It's been years so I've probably forgot something (like adding back boiler antifreeze in some systems)

But you can see that what you're paying for is not the part but the time and knowledge the service tech has to have to do the job right and not leave you with leaks or no heat in cold weather.

By the way, what cost were you quoted?

Do I need to replace a boiler gauge if there's moisture inside the glass?

Do I need to change the gage when there is moisture on the inside of the gage glass but the gage indicates correct temp and pressure readings? Thank you. Janis On 2021-09-06 by Janis S

by (mod) - yes change the gauge

@Janis S,

Yes you should have your heating service tech change out that leaky gauge.

It's not usually an emergency, so you can schedule that for your next service call - before the oncoming heating season.

The concern is that water in the gauge tells us that there is already an internal leak in the gauge.

Ongoing corrosion, or temperature change that cracks the gauge glass, or even simply accidentally whacking the leaky pressure gauge could result in its bursting;

Watch out: If that happens the result can be a boiler room or basement flood, loss of heat, and if the boiler is quite hot, even a scalding burn if someone is nearby.

I've seen leaky gauges left in place for years with nothing worse happening than that the gauge becomes un-readable. But on my boiler, rather than risk the dangers I list above, I'd have the gauge replaced.

Where do I buy a replacement boiler gauge?

I repete where can i buy a replacement pressure -tempurture gauge? @clint collingwood,
temperture

Where can I buy a repiacement guage? On 2020-11-28 by clint collingwood

by (mod) -

Plumbing suppliers, heating suppliers, online vendors, even Amazon.com all stock these boiler pressure and temperature gauges as it's a very common part.

Just check the pipe size, typically 1/4", of the threaded base of your boiler gauge.

Boiler Pressure Too High FAQs

When my heating boiler turns on pressure goes up to 30 psi and the pressure relief valve drains

I am stumped. Weil McLain hot water boiler is filling to 20lbs PSI cold. Three storey home.

When calling for heat the pressure goes up to 30PSI and PRV bleeds.

Expansion tank (old 4 foot long tank not bladder) seems to be taking some of the water. Any ideas? On 2020-05-07 by JH

by (mod) - relief valve leaks when boiler gets up to high temperature

20 psi cold is a bit high- typically we'd see 12, at a hydronic boiler. 12 psi is usually NOT enough to get hot water up 3 floors. But 15 psi is enough. So 20 is probably too high.

Sketch showing boiler psi readings vs. highest radiator in the house, courtesy Carson Dunlop Associates.

Check also the temperature: if it's going above 200F then that's the problem.

At EXPANSION TANK PRESSURE ADJUSTMENT

we discuss setting the heating boiler expansion tank pressure to accommodate tall buildings

Watch out: Also see the diagnostics and safety warnings beginning at

RELIEF VALVE LEAKS

by JH - discovered waterlogged boiler expansion tank

Think I figured it out. Expansion tank was FULL after all.

Reply by (mod) -

Way to go -
waterlogged expansion tank

Still starting at 20 psi cold is a bit high

Weil McLain boiler gets too hot, pipes bang and gauge maxes out at 250 degF

My Weil Mclain CG boiler temp keeps rising until there is loud banging in the pipes...the temp gauge maxes out, 250f.

can't seem to get the temp to stop rising, autostat is set to 180 and the psi is around 15.

Any ideas why temp keeps rising / suggestions on what to check and how to address?

Thanks in advance! On 2020-04-17 by Jerry

by (mod) - Watch out: your boiler is unsafe, risking an explosion, turn it off

Jerry,

Watch out: That sounds very dangerous to me. At 250F if your relief valve on the boiler is not spilling you risk a BLEVE EXPLOSION

Turn off the system immediately and call for repair.

My boiler pressure keeps going past 30 psi

Whats the right water temperature setting for a Hydronic Boiler for a two-family house in Brooklyn New York ? And why I can't keep my boiler at 12PSI it keeps going past 30 PSI my expansion tank is new. On 2022-12-23 by Nathan

by InspectApedia (Editor) - What's the right water temperature setting for a Hydronic Boiler

@Nathan,

Your boiler temperature will be as low as room temperature when it hasn't run in some time and will heat up to somewhere under 30PSI at its hottest.

If the pressure in the boiler exceeds thirty psi, the pressure temperature relief valve will open to avoid risking a boiler explosion.

You don't set the boiler pressure you set the boiler operating temperatures by adjusting the boiler's aquastat.

We explain the usual boiler temperature settings

at AQUASTAT HI LO DIFF SETTINGS

Watch out: If your boiler's starting pressure when cold is higher than 12PSI that could be your problem. In that case, when the boiler is OFF and COLD, drain water to drop the pressure to 12 psi.

Water pressure in the boiler is at 40 psi with the boiler water being cold

Hello, I just drained out my hot water boiler, this is a three story house. I installed a new pressure reducing valve which came preset at 12 psi. I also replaced the pressure relief valve and expansion tank is also at set at 12 psi, the old one was full of water.

I filled out the the boiler and bled the air from the radiators, but my water pressure in the boiler is at 40 psi with the boiler water being cold. Am I going to have the same problem with constantly losing water? thank you- Please help! On 2022-09-12 by GEORGE.B

by InspectApedia-911 (mod) -

@GEORGE.B,

Watch out: don't even turn on the boiler before you know its cold-pressure is correct - probably 12 psi.

Either you've had street level pressure, bypassing your pressure regulator/water feeder or your pressure regulator is improperly installed or damaged.

Have you tried draining pressure from the system until it gets back to 12 psi?

Do that and if pressure stays there you're good to go.

Also don't rule out a pressure gauge that's stuck. Tap gently on the gauge to see if the needle drops.

My Argo Electric boiler psi and temperature seem high according to standard

Good day! I am writing to see if I might get some feedback if someone is available. Just got the system up and running yesterday, a 16 year old ARGO hydronic electric boiler.

The house is comfortable today, and the temperature gage has been consistent.

I have a bit of concern about the psi and the temperature seeming high according to standard said I have read about online.

And I cannot remember what the cages were reading last year. Psi is 22, temperature is 140, steady and consistent. Would anyone advise perhaps a new expansion tank? Thank you! On 2021-10-14 by Julia

by (mod) - your system is operating normally

@Julia,

An expansion tank absorbs the initial pressure increase in a hydronic heating system so as to avoid dumping the pressure/temperature relief valve.

But the expansion tank has NOTHING to do with the ultimate temperature and pressure that the system will reach. Those are set by the aquastat or control over the boiler's temperature.

Your boiler pressure is about 23 psi and its temperature about 140F.

As long as you're seeing pressures that are below 30 psi (the typical PRV dump pressure) and temperatures below 200F your system is probably operating normally.

If you don't have the manual for your boiler see the Argo boiler manual downloads and contact information found at

ECR INTERNATIONAL BOILERS HVAC AGE MANUALS CONTACT

Boiler Pressure Too Low FAQs

Benchmark 1000 Boiler gauge pressure too low: reads zero at 160 degF

Benchmark 1000 boiler, my gauge pressure is zero while my temptress on same Guage is 160 F. On 2020-03-25 by Jay trinidad

by (mod) -

Jay

If you've got heat then I suspect that the gauge pressure sensor port is debris-plugged.

Boiler pressure gauge reads zero and boiler turns off

I have no pressure on my gauge and the boiler keeps locking out - On 2020-02-23 by Bill

by (mod) - no water pressure in boiler? Check the gauge itself

Bill:

Because sometimes the gauge itself can be debris-clogged and not register pressure, you may need to check elsewhere to find out if indeed your boiler and the heat piping are not filled with water.

Go to a high location in the building where there's an air bleeder and open the valve (carefully so as not to get scalded) to see if water comes out - if so then there is probably water in the system and the lockout may be due to a burner or safety-reset issue.

If the boiler really has no water then a low water cutoff could be shutting down the boiler to prevent damage or an unsafe condition or even a BLEVE explosion.

So if in doubt leave the system off and call for repair.

Let me know.

Boiler pressure gauge never gets above zero but my boiler works fine

My hydronic heat boiler has a combination temp/press gauge installed in a sealed well.

The temperature seems to work fine, but the pressure gauge has never move off zero. How would it work in a sealed well? I'm thinking of installing a separate pressure gauge on the system that is not in a sealed well. On 2020-02-12 by Brad

by (mod) - boiler pressure gauge not working

Agree, Brad, the pressure gauge would need to be able to sense water pressure from the boiler.

But are you sure we're seeing an original installation by the manufacturer?

It's not likely that the manufacturer would install a temperature/pressure gauge in a sensor well that is intended only for temperature sensors.

Attach a photo of your gauge.

Is 180 degrees F too hot for my Weil McLain boiler?

Temperature on my Tridicator is 180 degrees farenheit. Is that too hot for a Weil-Mclane 150,000 BTU boiler that is 35 years old with a Honeywell R7184U Transformer ? v

by (mod) - no

180 F is a common upper limit set on heating boiler systems by service technicians.

Crown boiler is hot but my radiators are cold and no water is getting to them

I have a Crown boiler. The pipes in basement get hot the temperature shows temperature but the water gauge shows 0 psi.

I tried bleeding the radiators and filling with water no air or water comes out.

I replaced pressure relief valve and tried filling the boiler but no water is getting to radiators, butthe boiler is filled with water please help. Thank you. On 2021-02-24 by Jpusfinc

by (mod): sounds like your system is air-bound

@Jpusfinc, in the ARTICLE INDEX at the bottom of this page you will find several articles on

repairing an AIRBOUND HEAT SYSTEM and

others on NO HEAT - BOILER problems for hot water or hydronic heating boiler systems.

In the latter case besides resolving the Airbound question you need to look at the thermostat, thermostat wiring, circulator relay, and circulator to see if the circulator is even running.