Burnham Boiler - Aquastat Issue?

ElvisWashington

This is for a medium-sized church. We have a beast of a Burnham boiler in basement, I would guess 40 years old.

On it (hot water not steam), every couple of days, the pressure relief valve goes off and dumps steam all over the utility room, with loud clanking throughout the radiators. The pressure gauge remains constant at about 20 PSI but the temperature gauge reads 230 degrees (thus the steam and relief valve).

The pump motor seems to be fine and circulates well when it is running as expected. The aquastats are set to 160 degrees.

It is random. When it's running fine otherwise, the temperature stays between 150 and 160 degrees according to the gauge.

The system was filled and bled at the beginning of the season. My theory is that one of the two aquastats (probably also 40 years old - Honeywell) is failing randomly, causing the boiler to keep firing past the point it should, overheating the water. If I shut the system off or release all the pressure through the valve, it operates fine again for a day or two.

Any ideas that I am not considering? All suggestions and advise are most appreciated, thank you in advance.

109A_5

Hello ElvisWashington,

The pressure part of the gauge may be broken.

Do both aquastats serve as a redundant boiler high limit ?

Aged pitted electrical contacts can stick closed.

ElvisWashington

Thank you @109A_5 I just figured out that one of the aquastats turns on the pump at 120 degrees, and the other one turns off the burners at 160 degrees (er, it seems that is how it is supposed to work).

ElvisWashington

Here is the boiler spec

EBEBRATT-Ed

A boiler that size should have 2 high limits wired in series. 1 should be a L4006A and the manual reset control should be a L4006E (I believe that is the correct #)

You should have this fixed and the wiring check. Runaway boiler system is not good.

You aquastat in the picture set for 160 looks like it may be a strap on aquastat (strapped to a pipe). If that is the case that is not good the high limit should be an aqua stat with a well inserted in the boiler water.

HVACNUT

The tridicator looks like the newest thing on the boiler, but that doesn't mean it's correct. If boiler temperature is getting getting to 260° when its set for 160°, then obviously that's a problem. A boiler that size should have immersion well aquastats, not strap on aquastats IMO. It's 300K input, so I'm sure the pipe size isn't 3/4" coming out of the boiler. So how can there be an accurate boiler temperature reading from a 3/4" pipe away from the boiler? And as @EBEBRATT-Ed said, there should also be a manual reset High Limit. See if there's a way to get an accurate boiler water temperature. No other controls? No outdoor sensors?

The relief valve blowing could be a seperate issue, unless it's a pressure AND temperature relief valve. Typically it's just a 30 or 50 psi relief valve in a boiler. No temperature. So actual psi at limit needs to be tested. I'll assume it's an air control system, so is there an expansion tank in the ceiling that needs to be drained? Maybe, maybe not. Because if the tridicator IS correct, and pressure was at approximately 25 psi @ 260°, then a properly functioning relief valve would NOT have discharged at that pressure.