Boiler pressure and temp low, on-demand installed

Burnham boiler from 1998. They proabably turned down the temperature to save on heating costs since they have an on-demand water heater installed to provide for the kitchen and single bathroom (home was only 740 sq. ft.), but the boiler pressure was low. Seems like the pressure should be up around 12-15 PSI despite temperature setting. Also, with water temp this low, are they risking the growth of microbes in the system?
I wondered about the cans, which were empty and dry. Air vent looked fairly clean. Nothing looked wet. Do expansion tanks have a release valve which can release water? If that were the case, they should all have paint cans under them.

15-20 psi would be about right for a two story home with a basement and the boiler on the basement level. Approximately 5-8 psi per 10 ft. above the boiler. Depends on the highest radiator served above the boiler. Why is the boiler on in the summer anyway if it’s not providing domestic hot water?

It’s a closed system and should have a boiler treatment in the circulating water.

No, The TPR which doesn’t look quite right because of the nipple extension is in the same water stream as the expansion tank.

Who knows. May be a poor attempt to add some humidity to the home. The blue cap on the bottom of the expansion tank is to add air below the bladder.


With those readings the boiler had to be “OFF”, or if the boiler was “ON”, then the gauge is inoperative.

The blue paint bucket (on the floor) is placed under the backflow preventer (which is missing the 3/4 inch copper extension pipe). It appears that the backflow may be dripping when the boiler is in full operation.

The paint bucket under the expansion tank appears to be catching water that drips from the air valve above it. It needs replacing.

Was this boiler in full operation with those stat readings?

I took the temp/pressure gauge photo first time around the home exterior (boiler located in a little addition) and hadn’t yet turned up the thermostat, which I found turned all the way down. Didn’t yet know about the on-demand, either.

Boiler fired right up when the thermostat called for hot water, so although before I turned up the thermostat hot water wasn’t actually circulating, the system should still have been at operating pressure. Pressure in the pipes shouldn’t drop to 2 PSI just because the circulation pump’s not running.


The PSI and temperature needles will drop back down due to the boiler not being in operation. That is a operating temp and pressure gauge.

When you turn that boiler on, the water is being drawn and the operating pressure will now adjust the black needle on that gauge. Also the red arrow is not set correctly. When I find these set incorrectly, I always turn the glass cover to place the red arrow at 30 lbs. and tell my client that the PTR valve will start leaking if the black needle gets anywhere near the red arrow.

The PRV on the makeup water inlet should be set to pressurize a cold system to 12 PSI, then the pressure rizes when the water heats up and they usually run somewhere around 15-18 PSI.

If there’s water dripping from the air valve on the bottom of the exp. tank, then the diaphragm is shot and the tank needs to be replaced. The auto water feed could be off because of this problem.
Which means it’s time to get a plumber to change the exp. tank and bleed the convectors or radiators. It’s probably air bound now.:cool: