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Where did the air and noise go?
We moved to a new house last winter that has hot water heating (so much more comfortable than forced air - a very pleasant surprise!). Here's the background: Mid 1980's vintage Burnham boiler 266k input 190k output with 5 zones, 2 fin tube and 3 pex, and a single taco 007. I had a chance to meet the previous owner (nice guy who had built the house) and he talked about the "comforting" sound of the boiler banging on a cold night. Apparently it had done that for a long time.
Not long after we moved in, a zone valve started leaking and the rate increased rapidly starting on a Friday night. The zone it was on had had a tap added to it (for staple up pex under the master bath floor when it was given a minor remodel, probably to help sell the house). The tap was added between the zone valve and the 1.25" manifold tube, meaning that it was sweated in about an inch from the valve. I think that's why that one valve failed. It took 30 minutes of patient chiseling to get the valve seat out, but I was able to replace the valve head with one from the local hardware store before the house got too cold. It left me thinking that the initial installation was good, but that later changes maybe weren't as well thought out.
In the spring, I pulled about 3/4 of a gallon out of each zone and a gallon or so from the boiler drain. The water had some grit and rust in it, but wasn't too bad. It also had ethylene glycol anti-freeze (I'm pretty sure - there was an ethylene glycol tester left behind next to the boiler). I added two quarts of Hercules boiler and heating system cleaner to try to suspend any scale (I'd hoped that would quiet down the boiler but it had no effect).
This fall, the first time I tried the heat, it didn't come on. the circulator (taco 007) had stopped working. I had to drain abut 6 more gallons before I could replace the pump, but that got the heat back. I closed the purge and drain valves then let make up water re-fill the system. My hope was that all the air would be taken out by the air vents on a separator and one mounted on the boiler by the relief valve. I replaced the air vent but it showed no evidence of air being released (no sound of air coming out, no drips or stains from any moisture leaking past the separator). I can imagine that the oxygen in the air would be bound by the rust and grit, but the ~80% of the air that was nitrogen shouldn't have had anywhere to go but the vent. There are no gurgles, all zones heat well. There's no sign of air in the system.
- where could the air have gone?
This fall, I drained another 6 gallons and added 5 gallons of cryo-tek 100, plus sludgehammer corrosion inhibitor, plus another quart of "leave in" cleaner. The boiler never banged again. Both the cryo-tek and corrosion inhibitor mention having silicon to lubricate heating system parts. Did that help with the banging?
- was the banging from movement between boiler sections and the silicon lubricated it? I've been doing a lot of reading and haven't found any mention of boiler sections making noise when they expand and contract, but can't think of anything else that might have been causing it. It used to sound like a muffled shotgun was going off inside the boiler and the attached pipes would shake. The noise wasn't from pipes or fin-tube units (still plenty of that). it used to come from the boiler.
Is this typical? (some chemicals causing that change)