Central heating noise

[letham]

When i turn the central heating off i start getting very loud bangs in the pipes running to the attic and in the attic. It does not start till about a good half hour after turning off the heating off and the noise will be intermittant for hours. the system was drained down a few weeks back and all the radiators have been bled. I was thinking it could either be trapped air or a water hammer effect but as i say the rads have been bled and the noise doesn't start till a good half hour after the heating has been turned off. Someone suggetted it could be the dump valve going back to the header tank but to be honest i m not sure what he means.

any help would be great!

 

[noonespecial]

1.What make and type of boiler.

2.Have you got a feed and expansion cistern or is it a sealed system

3.What heating / water services equipment have you got in the attic.

4.Have you got a hot water cylinder.

5. Any other information you can provide may be useful.

6.Do you know if noise is from heating system or domestic hot water system?

7.Do you get any noise as the system heats up?

8. Could it be expansion noises from the pipework?

 

[Nige F]

Dump valve to header tank...........was it a mechanic,or car enthusiast?... a dump valve is on a turbocharger pipework........so he wasn`t a million miles off and water can spurt from the vent pipe into the Feed+Expansion cistern Not necisarily your prob. tho`