My heating arrangement is a two-zone hot water system fed by a 24 year-old Ultimate oil-fired boiler.
The previous (and original) owner of my home maintained the system well; it's provided five years of uninterrupted service since I purchased the home. I have a service contract with the local oil company, which provides a yearly cleaning/tune-up. I've done some basic stuff on it myself, like install a new aquastat, and run new lines to the oil tank.
After the most recent tune-up, and firing the boiler for the first time in late summer/early fall, I began to hear a loud, metallic banging noise coming from inside the boiler. The noise could be heard throughout most of the rooms in my home, as it reverberated through the pipes.
It seemed to appear when the boiler first fired, would last a few minutes, and then stop once the boiler reached operating temp, only to be heard again whenever the call for heat would be satisfied (like a car or truck engine "dieseling" after you shut it off).
I've had a tech come out it look at it three separate times; they installed a new high-hat vent, bled all the baseboards, made sure the cut in/off temps were set correctly, added some cleaner to flush out sediments, and drained the boiler down to add fresh water.
The noise intensified somewhat after the flush, in that it sounds "clunkier" and less metallic than previously.
Despite the noise, the system is still supplying heat to all of the baseboards on both zones.
I'm stumped, and so appears to be the oil co, as they say there's nothing left for them to do, other than install a new boiler.
Could the boiler in fact be damaged beyond repair, or is this just a case of the oil co not wanting to run up the "free labor" of my service contract on something they can't figure out? Is there something they're missing?
Any advice would be much appreciated. Many thanks and best,