furnace banging noise
The hot water pipe above my furnaces produces a banging noise when in operation. there is no direct bleed valve on that pipe, but I have bled air out of other nearby bleed valves. analog temperature gauges on the furnaces and a digital temperature sensor on the banging pipe are reading 180 to 195 Fahrenheit, so I don't expect that the water is boiling. The banging continues and diminishes over about 30 seconds after the furnaces turn off as the digital temperature sensor on the pipe drops from 195 to around 185.