One Radiator Banging

homesteadbuilder

Have a one pipe steam system in a rental property. Tenant says loud banging at night from one radiator. Radiator is the furthest from the boiler. Checked to make sure valve is all the way open. Have plenty of pitch on the radiator. The issue is mostly at night but sometimes during the day. I have checked the pressuretrol and it cuts out at a little less than 2 psi. I have run the unit for several cycles during the day and have not been able to get the radiator in question to bang. The tenant is very good and I have no reason to doubt what she is telling me. Any ideas or any good steam guys you could recommend to check it out. I'm in Bergen County , New Jersey. Thanks

ethicalpaul

Forget the pitch of the radiator, that's not the problem.

There is likely a place in the supply pipe leading to that radiator where there is a sag (probably due to settling) that is collecting condensate (not allowing it to flow back to the boiler).

After a long time with no heat (presumably you are running a setback at night), that "trapped" water will cool. Then when the first call for heat comes and steam comes in contact with that water, it causes the banging.

After that the water is warmed up and no longer causes the banging (but may still cause gurgling sound depending).

Can you access the supply pipe for that radiator? If not you can try lifting the valve side of the radiator by 1/2 an inch every few days if it will let you. This might lift the saggy part and allow the water to drain.

homesteadbuilder

Thanks for the reply. I should have added that I thought that might be a problem and had added a block of wood under the valve to raise the line under the floor to create as much pitch as possible. I was probably able to raise the valve about 1/2 inch and just left the block of wood under it. I then shimmed the radiator to make sure it still has plenty of pitch. Most of the other radiators are very close to their riser. This radiator is in the bath and is probably 5 foot away from the wall that the riser comes up so there would be a 5 foot horizontal run under the floor. There is a second radiator coming off the same riser. I have checked that to make sure it has plenty of pitch also. The thermostat is an older Honeywell with no set back capability. One more thing as a test I put a small oil filled electric radiator in the bath and shut the valve completely thinking that at least they could make it thru the night with no banging and then open the valve in the morning. The tenant said that the banging was even worse and opened up the valve. Could there be a valve issue? I thought with the valve shut there should be no steam getting to the radiator and therefore no banging. I assume the banging was in the riser and not the radiator itself. Again thanks for the reply.