Central heating is posessed

[Gungnir]

If anyone has knowledge of central heating systems on here could you offer possible diagnosis?

About an hour after boiler turns off at night there is noise from the pipework. Starts as a low pitch rumble building to a high pitched screech over a few seconds then stops. Only does it once.

Radiators bled. Boiler pressure fine.

Any ideas?

 

[Buffman]

Pressure surge from something like a valve turning off too quickly and the pipework not being well mechanically fixed to the walls/floors etc.

Not sure if you get air valves in standard domestic heating? I think I have one but it's on my outgoing hot water rather than heating line.

(read up water hammer).

 

[Skiddley]

Do you have a water hammer arrester installed?

 

[Vern1961]

When was it last drained/cleaned or power flushed?

Have you also bled the pump and the air release valve (if an open system) on top of the pipework where the water circulates from the pump?