Combi Boiler Rattling Noise

[katherhi]

My combi boiler makes a rattling noise after if has been on for about an hour. If I turn down one of the radiators the noise stops temporarily but then starts again and then I have to keep turning the radiator dial either up or down for the noise to stop. I have bled all of the radiators on a number of occasions and checked the pressure and is ok. Its seems to be the pipes rattling. Do you know what causes this and how it can be fixed. I recently had a maintenance check on it and everything was ok and dont particularly want to spend more money on someone coming out if it is easily fixed. Can you help?

[dothawkes]

I have no technical understanding of combi boilers, but mine used to rattle when the water got too hot.  Turn the wall dial down AND the one on the front of the boiler, no idea if that should work for you and actually no idea if it really worked for me but the rattling seemed to go. 

[tony1941]

I've had the same problem - it seems to be the thermostatic radiator valves.  These often state on the packing that they work either in the flow or the return, but can you really beleive that??  Probably change ends of the two valves on the guilty radiator (easily found when rattling by "taking its pulse" with a finger, and it will go away.  Try just a tiny adjustment of each valve in turn as another search method.

[pezza.......]

I had this problem in a previous house.  The builders put it down to the gases caused by the oxidization of the new pipes.  I chemical is usually added when a combi is fitted to prevent this happening but it didnt do much good. 

The only way I could stop it was turning the primary rad up or down.

[Tim Baxter]

Turn all your rad thermostats up to full.  If the noise stops then you know it's the 'stats restricting the flow of water.  'Stats used to be one-way, some are now 2 way, if your 'stats were fitted the wrong way then the noise would be instantaneous.  After you've checked your 'stats call a plumber.  Additives to the system,a, lubricate the pump,b,inhibit corrosion in the boiler and rads (not pipes),c, act as anti-freeze,d, have a bubble effect so if there is a leak you can see the liquid bubbling out.  The amount of initial corrosion (in fact never) in copper pipes is zero, the builders were spinning a yarn