it is a weil mclain He-5 ser 3 put in in the mid 1980s w/ grundfus UP26-96F pump(looks to be about same age).
It sounds most like an ele water heater that has some build up in it, but no poping noise like you would here in a gas heater with a lot of buildup. I have heard several boilers with condensation and it sounds different than that. Jim
Boiler heat exchanger makes humming / buzzing noise
My customer has a Cast Iron boiler that makes a sound similar to the sound a noisy electric water heater makes, a humming or sizzling noise. It seems to do it when it is heating up but not every time and it will start and stop at different temp. My first thought was air in the boiler but I bled it out and there was very little in it. Then I thought about calcium build up, but this is a fin tube system that has had no leaks. Plus it is feed with soft water. I also checked for a leak in the exchanger looking from the top down and the bottom up but can see no evidence of a leak. The owner says he did not here the noise last heating season and it seem to show up all at once.
Does any one have any ideas?
Not getting a clear take on your noise. Possible condensation dripping on burners (sizzling sound)? Or is it a rumble like a percolating water heater, caused by sediment build-up? Boiler make/model and same for pump?