Thermal Store problem after replacing radiator

[markbebb]

I have a 9 year old system, with seperate boiler. After changing a rad and cleaning out the system, I have the following problem:

hot water is fine and the store heats up well.

When the Central heating pump comes on, the tank makes 2 noises like air is expanding or something, (sounds like a clunk clunk) then the same when the pump shuts off. Looking at the top up tank when this is happening I can see a small amount of hot water from the store expanding back into the tank.

I have bled the rads and am now out of ideas.

thanks
Mark

 

[ChrisR]

Is it a motorised valve which is making the clunk and letting air through?

Hope you have loads of inhibitor in that tank...

 

[markbebb]

No Chris, its comeing from the storage tank itself.....it sounds like the tank is flexing in and out briefly.