Central heating knocking

steveandel

We've just moved into our house and we've found that sometimes when the heating is turned on there is a loud continuous knocking noise coming from somewhere in the pipes. It sounds as though someone is using a hammer drill on the other side of the wall or something like that! It seems the only way to stop it is to turn the heating off, leave it for a few hours and try again. Is this likely to be a problem with air in the system which can be easily fixed? The strange thing is that it doesn't happen every time the heating is turned on, probably only about 1 in 8 times. Occasionally it also starts doing it when the heating has already been on for a while with no problems

Thanks

monkeydust_2

ehh bizare I also have this and was wondering what the problem might be... anyone?

penrhyn

Could be boiler temperature or air in the system.
I guess you have bled you radiators. Are your radiators excessively hot?

shelly

I *think* but could be totally wrong that when we had knocking pipes it was air in the system. Hubby bled the rads and the knocking stopped.

steveandel

I did think it might be air, I just need to get hold of a radiator key thingy now.

re: penrhyns comment, the radiators are pretty hot, but I think this is down to the fact that we have a combi boiler without an external thermostat anywhere in the house Therefore the only way to set the temperature of the heating is on the knob on the boiler which ranges from small arrow to big arrow :rolleyes:

Motty_2

We had a extremely loud knocking from the airing cupboard which sometimes started when the heating was on, apparently it was the "three way valve" that had "bit" come loose.

Not much help I know

Richard

penrhyn

If its a combi and you bleed your radiators you should do this with the boiler OFF. When you are done check that the pressure gauge on the boiler is reading the appropriate level for your system, if its low let some more water in via the filling loop.
I guess that your system has thermostatic radiator valves, if not you must be spending a fortune on gas, are you sure that the programmer hasn't got a built in thermostat?

alanobrien

Could be air in the system, pipework hitting against floorboards or rafters, boiler kettling, or a TRV fitted the wrong way around, pump running to fast,
amongst other things..

I had a rad "knocking" and found the pipework straining as it came through the floor. I fixed that and now it plays a tune instead, which means there is another issue elsewhere and i suspect the TRV. One thing leads to another......

steveandel

penrhyn wrote: »

If its a combi and you bleed your radiators you should do this with the boiler OFF. When you are done check that the pressure gauge on the boiler is reading the appropriate level for your system, if its low let some more water in via the filling loop.
I guess that your system has thermostatic radiator valves, if not you must be spending a fortune on gas, are you sure that the programmer hasn't got a built in thermostat?

Thanks, I'll try bleeding them when I get a chance. The pressure gauge seems to be ok, (the manual says it shouldn't be below 1 bar, and the gauge goes up to 4 bar, usually it is around 2 bar).

Some of the radiators do have thermostatic valves but not all of them! The others just have the old twist on/off valves. It's not too much of a problem because at the moment we only have the heating on for short periods during the day anyhow, but it is slightly annoying that we can't just set a temperature instead of having to go and turn the boiler on/off the whole time!