Pressure issue

jeckert · November 30

My system is a 100 y.o. American standard boiler. The aquastat was set for 155 degrees. The burners would run and shut off at the set temp of the aquastat however the pressure would be half way in the red between the 30 and 50 on the dial so the burners would shut but then something would shut the gas off to the pilot. Im guessing this is a safety thing due to the pressure being in the red. My question is what would cause the pressure to get so high. Ran fine the last 3 yrs. This yr the pilot assembly was replaced along with the thermocouple. 2 yrs ago the pump was replaced along with the expansion tank, pressure relief valve and something else I can't remember.

pecmsg · November 30

Are you reading the inner dial Red (Altitude)

Or the Outer dial Black (PSI)

neilc · November 30

just out of curiosity, what are you keeping in, or out, with the screen around the vent diffuser? make sure the screen stays clean

EBEBRATT-Ed · November 30

If the pressure is really getting over 30psi you should shut the boiler down and have the safety valve changed.

Its is possible the pressure gauge is bad and the safety valve is ok but don't take chances. You can buy a temp gauge with a hose connector to put on the boiler drain valve to check the pressure.

I would strongly suggest doing that.

You could also have a leaking water shut off valve.

But I would suspect your expansion tank could be defective.

But check the pressure with a new gauge first.

DanielDAY · November 30

Just so we are clear, you are reading 30-50 psi where the word “limit” is in between while the boiler is running? That would be a problem and you should see water near the pressure relief valve if it got over 30psi. I would do what @EBEBRATT-Ed said.

I’ll add that you can even go to the expansion tank and press the shrader down to see if water comes out to test if it’s water logged. If you have the ability, see how much pressure is in the expansion tank too

hot_rod · November 30

when was the expansion tank replaced? Is that when you would see high pressure conditions.

The tank pre-charge needs to be checked.

Looks like some large diameter piping, expansion tank could be a tad small also if everything is charged properly and you see a wide pressure swing. looks like it had maybe a 30 gallon compression style tank in the joists?

You would need to drop the system pressure to check the expansion tank pre-charge.

Pressure issue

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