Hammering on boiler shutdown

Jshine

This is happening on a random basis.  I have a 1 pipe system that runs below 2 psi - thermostat set to 1 cycle - very quiet and even heat system - except - 1  radiator hammers (sometimes) when the boiler shuts down.  I think I tracked it to a radiator on the second floor and best I can tell it's on a pipe which is a straight shot from the basement - no other radiators attached.  What are the typical things to look for??

John

BobC

Check the piping

Make sure all the piping is sloped so water can find it's way back to the boiler and check the pitch of the radiator to be sure condensate can get out of the radiator.



Does this radiator heat up ok?



Bob

nicholas bonham-carter

radiator hammering

what sort of vent do you have on this radiator?

are you sure it is water-hammer, and not the sound of expanding/contracting metal rubbing against a wood joist?

how do you know that your pressure is really following the settings of the pressuretrol?

is this riser closest to the boiler, off the main?--nbc 

Jshine

hammering

Radiator heats up fine and looks like maybe as much as a 1 inch pitch to the supply side - maybe too much pitch? 

Jshine

hammering

the vent is a maid of mist 'c"  - 

- just from the 30psi gauge and the pressuretrol is at the lowest setting i could get it without it coming apart.

....is this riser closest to the boiler, off the main?--...    not sure what you mean -

BobC

a bit much

A 1" pitch on a radiator is a bit much, try reducing that to 1/8-1/4" and see if it makes a difference. Also there could be a short horizontal pipe from the riser to the valve that doesn't have the right pitch; problem is it's hard to tell when it's behind a plaster ceiling, you could try raising both ends say 3-4" so everything gets a boost (might want to wait for warmer weather to try - just in case) - just be careful, you don't want to crack a pipe. make sure you maintain some pitch on the radiator.



One more thing make sure the radiator valve is open full.



Bob

will smith_4

Radiator hammer

How big is the radiator? Could be that it's sagging in the middle sections, or it could be partially plugged with sediment/rust-which would impede the flow of condensate out.