Heating boiler gauge frequently-asked questions:

Questions and answers about how to read, interpret, or replace or repair pressure & temperature gauges found on hot water heating boilers.

This article series describes the combination pressure & temperature gauge found on most hydronic (hot water) heating systems. The boiler gauge gives helpful temperature or pressure readings that tell us if the boiler is operating normally.

Boiler Temperature & Pressure Gauge Guide FAQs

These questions and answers are about the pressure and temperature gauge on hot water or hydronic heating boilers were posted originally

at GAUGES, HYDRONIC BOILER - be sure to see that article.

My heating boiler has zero water pressure

Pressure & temperature gauge it does not show pressure at all. On 2019-10-04 by mike

by (mod) - Safety warning by moderator

Mike:

To be safe and because you've not confirmed that the boiler and heating piping are filled with water I have to say

Watch out: 1. TURN OFF THE BOILER immediately if there is the slightest chance that it is out of water - otherwise you risk damaging or ruining the boiler or even worse, causing unsafe conditions.

2. If the boiler in fact has plenty of water and works normally then most-likely it's the pressure gauge that needs replacement.

3. If the boiler does not have water and its automagic water feeder isn't working that device could be clogged and needs cleaning or replacement.

The Pressure gauge on Edwards Boiler shows zero pressure but the boiler is working OK

I have an old Edwards boiler it's full of water and is clearly functioning properly as it is heating up my registers and keeping my house warm.

The problem is my old gauge was reading zero pressure but still tracking temperature.

So I replaced the old gauge with a new gauge and it's still tracks temperature

but it's still reading zero pressure not sure what the problem is. On 2020-01-10 by Russ

Reply by (mod) -

I'm puzzled too, Russ.

Usually when the gauge won't show pressure it's because the small opening on the gauge base - that admits water to the gauge's internal pressure mechanism - is debris clogged.

When you replaced the gauge did you have to drain water and pressure from the boiler?

Where is the gauge mounted?

Is it possible that debris in the boiler water has clogged the pressure sensing port on both the old and new gauges?

Pull off the new gauge and inspect the (small diameter) pressure opening.

Also, as I describe at WATER PRESSURE MEASUREMENT,

I occasionally attach an independent water pressure test gauge on to a convenient spot on a hot water system to get an independent pressure reading.

You can buy a water pressure gauge pre-fitted with an adapter that connects to a standard hose thread.

That will match the threads on drains commonly found at several locations on hot water heating systems such as zone drains or the boiler drain.

Watch out: before making that test,

be sure you have a good quality hose cap on hand so that if, when you try to close that (seldom-used) drain valve,

if it drips or leaks you can install the hose cap to avoid a leak at the boiler - and keep water in the boiler while you wait for a repair.

Attach a photo of your Edwards boiler and its temperature/pressure gauge so that I can make a better guess at what's going on.

What's the normal pressure in a New Yorker heating boiler?

How much water pressure in a New Yorker boiler ? On 2019-11-14 by Anonymous

by (mod) - 12 psi cold, under 30 psi hot

Anon

For a typical 2 story residential home the boiler pressure would beast at 12 PSI cold.

You shouldn't be having to make an adjustment as I would expect your water feeder on the boiler to deliver that pressure.

That's the default from the factory. For taller buildings or other types of systems or other types of buildings those pressures and heating equipment could of course be different

Boiler Pressure Gauge Above 20 psi.

Pressure gauge on my boiler is way beyond 20 psi. What would cause this? On 2017-10-25 by Alex

by (mod) - normal as long as pressure is under 30 psi

If the boiler pressure is under 30 PSI and the temperature is under 200 degrees Fahrenheit then it's within normal operating range. If the pressure is over that amount you should turn the system off immediately as there is danger of a boiling liquid Vapor explosion or bleve

Also if the pressure is over 30 PSI I would expect the relief valve to be spilling so if it's not the situation is as I said, dangerous.

If temperature is below 200 and
If an independent measurement of pressure shows that truly the pressure is abnormally High, the system is still unsafe and should be shut off.

There are several causes of abnormal boiler pressure including leaks into the boiler from a tankless coil or improper water feeder. But it's also possible that the gauge of Simply defective.

 

What's the meaning of boiler gauge reading 60-80F & 20 psi?

What does it mean when the temperature gauge is reading between 65 and 80 F and the PSI IS 20. The system is producing heat in the hot water radiators in a six zone house at 5 am.

Is the temperature normal and if not what could be the cause? On 2019-01-14 by Ken

Reply by (mod): here are typical residential heating boiler temperatures and pressures

Ken, a residential heating boiler's normal operating temperature, measured in the water in the boiler, can be anywhere from room temperature to around 180 to just under 200 degF. Above that the relief valve would be expected to open.

Just what temperature and pressure you see depends on where the boiler is in an operating cycle.

Off, and not in use for many hours, the boiler will typically sit around 12-20 psi "cold" and temperature in the range you gave.

At the peak of it's operating cyle and fully "hot" the boiler will be at a bit under 30 psi and a bit under 200 degF/

 

Some of my radiators are cold; When I add water to the boiler pressure goes up, then falls back when I stop.

I have a combo system and a few cold radiators that I've bled. Still no heat. The pressure gauge goes up as I add water (opening the valve) but then goes back down again when the value is closed. Which is the correct reading? On 2018-11-14 by Bonnie

by (mod) - here are the diagnostics you need

I don't know, Bonnie, what is the correct pressure as I don't know what kind of heat you have for sure.

But if yours is a hot water heating system (not steam radiators) then the operating pressure in a residential system will normally be between 12 psi cold and under 30 psi when the boiler is hot.

I suspect that there is air in the heating system piping that has not been found and bled out adequately.

See AIR-BOUND HEATING SYSTEMS to read details of how to do that.

More diagnostic procedures for your case are at COLD HEATING RADIATOR REPAIR (hot water / hydronic heat)  

What is the correct temperature of a heating boiler system?

What is the correct temp of a broiler system supposed to be set at? On 2018-02-11 by Kathy

by (mod) - where to find boiler temperature settings

Kathy

Above at the end of the article at "Continue Reading" please see the boiler temperature settings given

at AQUASTAT HI LO DIFF SETTINGS

and don't hesitate to ask if you have further questions.

Viessmann Atola series G1n boiler pressure creeps up

I have a Viessmann Atola series G1n.

The boiler pressure rises to 30 to 32 psi during heating cycle, this causes the pressure relief to open on the combination fresh water regulator to drip.
Thanks On 2017-11-21 by Claude -

by (mod) - causes of relief valve leaks?

Claude

If you search using the search box above to read our articles on RELIEF VALVE LEAKS you'll see several causes including too-high incoming cold pressure at the boiler, leaks into the boiler from a tankless coil, a control that's letting the boiler overheat, or a water feeder valve that's leaking into the boiler.

When the pressure is as high as you cite, take a look at the temperature.

If that's under 200F then your start pressure is too high.

If you need the manual for your boiler or if you want to see our Viessmann serial number decoding guide in detail,

see VEISSMAN or Viessmann Boilers

Boiler temperature is at 180 F and the boiler is still running

Temp is at 180 & it don't shut off - On 2017-11-12 by Hal

Reply by (mod) - that may be normal

Hal,

If the room temperature is below the set temperature on the thermostat then the heat is behaving normally and the problem is that you're not able to warm the building enough to satisfy the thermostat. Of course if your baseboards are radiators aren't warm then we have another problem to solve and you'll tell me that.

If on the other hand the temperature in the room is getting above the set temperature on the thermostat then you're boiler isn't turning off when it should. You'll want to read this diagnostic article

https://inspectapedia.com/heat/Thermostat_Stuck_On.php

Turned on our new boiler but it doesn't work

Our gas boiler for the central heat was installed in November of 2016. Its not even a year old yet. The nights have gotten a bit cool and I turned it on to take the chill out of the air.

Since then, it hasn't worked.

That was a week ago. The owners manual doesn't help. The temp and pressure gauge aren't moving. There are no lights blinking to signify an issue. The gauge is all the way down. Its a cg-e gas boiler.
Any advice would be great. Thank you. On 2017-10-05 by Ashley

Reply by mod: take these steps

Ashley, we can probably get your heat going by having you step through the diagnosis and actions found at

• NO HEAT - BOILER

If those simple steps don't get your heat going then it's time to call your heating service company for repair.

Boiler temperature gauge doesn't agree with settings on the aquastat - boiler heats way above aquastat setting

The temp.guage and aquastat setting are far apart. The aquastat is on around 180---my boiler is going to 220.

I tried a new aquastat---same thing. Ihave a Dunkirk boiler.

We have used it like this for several years. It works fine like this. The pressure guage reaches the low 20,s.I was thinking of installing a temp. guage, but maybe this is not the answer.Thank you---KenOn 2017-08-19 by Ken

by (mod) - probably a bad gauge

Ken:

It would be unusual to see a boiler heat to above the boiling point of water (212 F) since you'd be making steam, and more-important, the pressure in a hot water heating boiler at sea level at 200 degF will be just under 30 psi, but up at 220F you'd expect the pressure/temperature relief valve to open.

So I speculate (picture your remote InspectApedia.com consultant sitting at her desk waving her arms in the air) that the pressure gauge is inaccurate, probably due to debris clogging with rust and sediment. I would replace the gauge.

The convenient time to do that is at annual service in the spring when you are not in the heating season, thus when it is convenient to let the boiler cool down and to drain water and pressure from it to permit gauge replacement.

Send us a photo of the boiler and a close-up of the gauge using the page bottom CONTACT link and we can comment further.

And double check your aquastat settings against the advice found

at AQUASTAT HI LO DIFF SETTINGS - Daniel Friedman

Can I add water to my boiler while it's running? - Pressure is at zero!

I have a Burnham oil fired boiler for baseboard heat, and the gauge(tradicator) the pressure is at 0 not 10 or 12 where is usually is, although we have heat coming through all baseboards up on top level (singe level home)

There is no heat in one baseboard in basement.

Question, is it ok for me to slowly add a little water from the house water supply feeder valve, to bring up pressure, while the system is running, I have read several posts, and now worry I might cause a crack or some damage. On 2017-03-10 by Mike

by (mod) - Check / replace the gauge before adding water to the boiler - it may be just a bad gauge

Mike:

It's possible that the gauge itself is what's failed.

Before feeding water, I suggest obtaining or making an independent pressure measuring gauge - see https://inspectapedia.com/water/Water_Pressure_Measure.php for an inexpensive solution;

I attach the gauge to the boiler drain, then open the drain valve just a bit - enough to put pressure on the gauge to get an independent reading.

If your boiler is at below 12 psi cold or even hot, then yes pressure is probably too low and it's appropriate to call for a repair. The trouble could be a bad water pressure regulator/water feeder valve.

There's a risk making the measurement I describe that the boiler drain itself is stuck or doesn't close again completely, leaving a drip.

1. Do not "force" the drain valve it it doesn't open

2. Have a garden hose cap on hand so it can be screwed over the drain valve opening in an emergency

Then about your cold basement zone: if the zone valve is open / circulator running, and that zone doesn't get warm,

see AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE

Where can I buy a gauge like the ones shown on this page?

Where can I buy a gauge like the one above ? On 2016-10-27 by Scott

by (mod) - plumbing & heating suppliers, building supply stores

Scott,

Replacement temperature/pressure gauges for heating boilers are sold at plumbing suppliers, heating suppliers, building supply stores like Lowes and Home Depot, and even online.

I just installed a replacement gauge on a heating boiler for a total cost of $10. as the gauge was used - salvaged from a boiler that was being removed. A new gauge is about $45. U.S.

Boiler gauge reads 0, boiler is at 180 F. Relief Valve is Spilling

I have a Peerless oil burner. The PSI on the gauge is at zero. The water temp at 180 degrees.

A pressure relief valve on the back side of the boiler is escaping steam and releasing some water. Hot water is fine in the house.

Thermostat set at 70, temp has dropped to 64. Boiler runs. Seems like no pressure on gauge yet pressure relief valve going off? On 2016-02-20 by Dave

by (mod) - defective boiler gauge - Watch out: unsafe boiler pressure or leaky PRV

Dave, I suspect that the boiler pressure gauge is defective, perhaps rust/debris-clogged. I'd have it replaced.

Separately, if the pressure/temperature relief valve is spilling THE SYSTEM IS UNSAFE and should be TURNED OFF. Call your heating company to diagnose and repair that problem.

Watch out: over-pressure at a heating boiler or water heater risks dangerous BLEVE explosion. (Search InspectApedia.com for BLEVE EXPLOSION to read details). That's why the relief valve is a critical safety device. Yours is doing its job.

See RELIEF VALVE LEAKS

to read the causes and repairs for spillage at that valve.

Water leaks into my boiler gauge - what does that mean?

Water is leaking into temp/pressure gauge. What does it mean? On 2015-12-20 by Anonymous

Reply by (mod) -

Anon it means the gauge is shot and needs replacement -which will require shutting off the boiler and removing some water and pressure.

Watch out: Ask for this repair before the leak becomes a catastrophe.

Leaks at my Valiant Boiler including at the drain, & into the pressure gauge

I have a Vaillant boiler installed in 1989. It is heating the house ok, except 2 short baseboards seem to lose heat and we have let out air manually on them and then they work for awhile. Also two bathroom corner baseboards are also not working.

One has a frozen valve and the other is not easily accessable behind a toilet. But it has not caused a problem and the rooms always have the doors open.

We have also drained the water tank twice near the boiler, but in the last few days, I have noticed a puddle of water under the boiler dripping from the boiler drain.

When the door to the boiler is opened the pressure gauge has alot of condensation in it and is hard to read. I am planning on calling our furnace repairman but need to know more about this problem?

If you have any ideas on this let me know.

Also I noticed it seem to leak water from the boiler drain when it is not running and not when it is running?

Thank you for your reply, but I just wanted to add that I checked the pressure and temp when the boiler was not running and when it was running and tried to see where the pointers were on the gauge(through the condensation).

When not running it was about 10psi and 70 degrees, and when running it was about 12 psi and 190 degrees. If it is working right, the pressure seems too low. yet it is heating most of the baseboards? Also, I am only setting the temp at 64 degrees because the daytime temp has been warm outside. I set it at 60 degrees at night. On 2015-03-13 by Kat

by (mod) -

Kat

If there is a leak at what is really the boiler drain that valve needs replacement and meanwhile can be closed with a screw cap.

If the leak is at a temperature/pressure relief valve that is an unsafe condition that needs proper diagnosis and repair.

And yes 12 psi hot is a bit low unless you're in a one story house - but then the gauge may be inaccurate.

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Continue reading at GAUGES, HYDRONIC BOILER - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see BOILER GAUGE REPLACEMENT FAQs

Or see these

Heating System Gauge Articles

• BOILER CONTROLS & SWITCHES
• BOILERS, HEATING - home
• EXPANSION TANKS
• GAUGES ON HEATING EQUIPMENT
  • BOILER GAUGE REPLACEMENT
  • GAUGES, HYDRONIC BOILER
  • GAUGES, STEAM BOILER
  • OIL TANK GAUGES
  • SIGHT GLASS, STEAM BOILER
  • SIGHT GLASS REPLACEMENT
  • SIGHT GLASS & HYDRONIC HEAT LOOPS on STEAM SYSTEMS
• PRESSURE & TEMPERATURE SETTINGS, CONTROLS
• STEAM BOILER PRESSURE
• STEAM BOILER TEMPERATURE
• STEAM BOILER SIGHT GLASS
• STEAM HEATING SYSTEMS & CONTROLS

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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