Boiler pressure at 40psi but relief valve rated at 30 psi not opening

ddombro · December 2022

I recently moved and the home with a hot water boiler system. I had it looked at by a professional a few months ago and he told me it all looked good and said I should check on it once in a while to see what the pressure read. He old me that 30 psi should be about the max the gauge should read but I recently checked in on it and it was about 40psi.

The relief valve on the system is rated at 30 psi but it wasn’t letting out any water so, i’m not sure if that valve is bad or if the pressure gauge is not accurate.

Also, the label on the side of the boiler says that the maximum operating pressure is 50 psi so, I’m not sure if 40 would actually be a problem or not. I’d appreciate any help or ideas. Thanks

EdTheHeaterMan · December 2022

Shut it down

Until you determine that the pressure relief valve is actually able to operate. There is a possibility that your relief valve is rated for 45 PSI or 50 PSI if the boiler is rated at 50 PSI. There is the possibility that the gauge is defective. You can check that with a pressure gauge that you can attach to a hose bib. Lawn sprinkler service tech use them all the time, and are available at plumbing supply, hardware and big box stores.

Verify the actual pressure with a "Known Good" pressure gauge. Don't rely on the old boiler gauge until you verify the accuracy!

Have a replacement relief valve available just in case it is bad, before you do this next test. Also available at Big Box, Hardware and Plumbing Supply store.

Operate the relief valve at least once a year. It says so in the instructions.
Pull up on the lever to cause pressure to release. One of 3 things will happen.

1. Water will release and then the valve will close and the water will stop. This is how it is supposed to work.
2. Water will release and then the valve will not close completely. It may drip fast or slowly
3. Water will not release. This is very bad.

If you get option #1 to happen then you are safe to operate. Go ahrad and turn the burner back on.

If you get option # 2 or # 3 to happen then be glad you have a spare Relief valve on hand to change it out.

EdTheHeaterMan · December 2022

Shut it down

Here is the reason why

The History of Safety Relief Valves

The first safety relief valve was created by Denis Papin, a French inventor who designed this device in 1682 to release steam from a digester. Steam pressure regulators were soon in common use throughout Europe. In the U.S., more than 1,700 boiler explosions and 1,300 deaths in the early 1900s prompted the widespread use of safety valves on these devices. The American Society of Mechanical Engineers was responsible for creating the first codes and standards for boilers, valves and valve modification methods.

Source: https://www.valsource.net/overview-of-safety-relief-valves/

ddombro · December 2022

Thanks for the great info, I’ll check it out!

kmb383 · December 2023

I've had this same problem for over a year. When we bought our house, I noticed that the pressure relief valve in the back of the boiler was leaking. The prior owner had the company who installed the boiler come out and replace it. I'm sure you know by know what that doesn't solve the problem. Since we heat primarily with wood, I didn't think too much of it. But an old farmhouse needs something else for a heat source in the cold months in upstate NY.

Our boiler was dripping from the pressure relief valve. I replaced it again and it started doing the same thing shortly after. Then I replaced the expansion tank as that was waterlogged. Although the tank needed to be replaced, it wasn't the cause of the problem but another problem that the original problem caused. Finally, after some research and education on boiler systems (I've had had a furnace in the past), I came to the conclusion that it was the pressure regulator. It went bad and was stuck in the open position. Since our water pump is set at 40/60, it was just enough to open the relief valve for a continuous drip when it was running. Easy enough, replaced that and everything is in working order again. Each part cost about $50 so the total was less than even having a boiler guy (or gal!) come out to look at. And since our local guy didn't fix it the first time, not doing it myself would have been an expensive mistake.

Good luck!

HomerJSmith · December 2023

One or two things are happening and must be addressed, pronto. Either the PRV is defective or the Tridicator (boiler gauge) is mis reading the true pressure. I suspect the Tridicator is inaccurate (not uncommon), but it must be verified. Attach a bibb gauge preferably a 30 or 60# gauge to the boiler drain and read the pressure in the sys. If it read over 30 psi replace the PRV and address the over pressure in the sys (usually misajusted or failed Pressure cold water fill valve or could be a water logged Extank) . If it reads below 30# at the Expansion tank pressure air charge replace the Tridicator.

rick in Alaska · December 2023

Also, and this is most common, make sure you are reading the proper part of the gauge. One side of the line shows feet in h2o, and the other side is psi. You might be reading the wrong side, and actually have about 20 psi.
Rick

MaxMercy · December 2023

Before I replaced my old boiler, I noticed one day the gauge was pegged all the way to the right, something like 100lbs or more. It stayed there after I released the pressure and was still reading over 100lbs the entire week it sat outside in the driveway waiting for the scrapper to come get it..

Those gauges do go bad, and as recommended above, do check yours with a known good gauge.

While I get that my gauge was bad, I don't understand how it got pegged all the way to the end of the dial, unless the default failure mode is designed to read too high than too low.. ??

STEVEusaPA · December 2023

Can you show us a picture of the gauge

Boiler pressure at 40psi but relief valve rated at 30 psi not opening

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Shut it down

The History of Safety Relief Valves

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