gas fired boiler sister-in-law lives in NYC and I'm in Ma. Already told her to check for pipes hitting anything. Boiler is one zone and bangs 2 or 3 times a day. Had a tech. from where she is look at it. One said "I don't know". The other one changed out HSI. Hard to explain to her what delayed ignition is. I asked her to look at PSI,all this over the phone,it was only 10psi. I had her pick up on water feed to see if water could pass thru,it did. Water feed valve(quick fill,whatever you want to call it)is bad. It will let water in but only manually. Would the pressure loss be a source of the banging?