occassional loud hum from boiler

Jeff Nucciarone

I have a Weil-McLain hot water boiler (gas) that is approximately 18 years old. It has developed a problem where on occasion it develops a rather loud and rythmic hum that occurs upon startup. It has a regular frequency of about .5 Hz-- humHUMMhum (pause) humHUMMhum (pause) etc.

The hum appears at random and only upon startup, and when it does occur it is usually when my zone 1 first calls for heat (although recently a zone 2 call triggered it).

The rythmic hum is so random it cannot be reproduced at will. Here's the real trick- when it does happen, I can make it stop by momentarily switching off the zone that called for heat when it happened. A fast boiler reboot, if you will ;)

The hum sounds like it is emanating from within the boiler coils. I had the system bled, I replaced the circulator motor control relay, and the high temp limit switch. System temp is not near high limit when it happens, and the relief valve is closed.

I am suspecting this is a resonant vibration triggered by something in the system. The randomness makes it difficult to isolate. Initially I thought it perhaps was triggered by a zone valve not openning fully, with its control motor vibrating as it tried to open the valve past its stop. Since a second zone triggered the hum, I'm not so sure! The system has 3 zones all controlled with Honeywell zone valves and there is a single Taco 007 circulator motor (replaced last year).

Anyone ever run into this before, and what was the fix?

Thanks.

--Jeff

Scott G.

Yeah, I'd check...

The circulator relay, many times it's a Honywell R8222 or equal, and is hummin' when energized. Turnin' power "ON"-:OFF" and it pulls in o.k. I'd replace em' if that's all you find... Good Luck

Scott G.