Good morning, We have 2 zone baseboard heating between the first floor and the basement. I have noticed that almost instantaneously with the thermostat clicking on there is a loud banging noise in the pipes. It does not happen every time but I would say at least 25% of the time. This is especially alarming in the middle of the night when it sounds like the house is going to explode. We have an expansion tank that is appr. 1 year old (Home Depot). A friend with some plumbing knowledge came over last week and unscrewed it to see if it was filled with water. It had some water but not filled. He also pressed the valve on the back of the tank and heard the hiss. He said there is pressure in there and so the tank is good. I have tried bleeding the pipes multiple times by just running the spout that comes off the furnace (white hose in pics) for a while but there is little gas left in the pipes. And yet the pipes keep banging. My questions are: Am I bleeding the pipes correctly? Does the fact that there is pressurized air in the expansion tank enough to call it OK? Any advice would be greatly appreciated. Thank you in advance for your help and advice.

My just-under-3-year-old FWH single-zone system (that some on this forum assisted me in choosing) recently developed a leaking pressure relief valve. The technician could find nothing obviously wrong. He zeroed out the pressure on the system, checked the #60 Extrol tank, which had been installed in late 2012,(6 months after the original installation of the system, replacing the #30 Extrol tank). Everything seemed OK, but it still ran up to 30 PSI, and leaked. It is an old home, about 2800 SF/2-story, converted steam system with huge radiators, huge cast iron piping, much water volume. Six months after the installation, at the new heating season, the #30 was blowing the PRV, so they put in the #60. It ran at 25-lbs, but it did the trick until recently. Just for fun today, when he could find nothing glaringly wrong, the technician decided to try a new expansion tank. When he was taking the old one off after depressurizing it, he slowly unscrewed it, holding it there momentarily as it more-or-less finished leaking. As he finished unscrewing it, and then while slowly lowering it, it suddenly and instantly sprayed a fair amount of highly-pressurized water for 3 or 4 seconds, like a gusher, sending a stream of water to the ceiling, as well as getting fairly soaked himself. He was shocked and indicated that that had never happened before. The new tank (HTX #60) seems to be holding at 25-lbs at full operating temperature—so I hope the problem is solved. Does anyone have any opinions on what happened, and if the problem is likely fixed? I have been charged $95- for the “diagnostic fee” and $133- for a “Misc. Repair”. $228- total. Have I been mis-treated? The Extrol tanks seem to have a 5-year limited warranty, but it is unclear how that all works. Thanks.