I have Potterton Netaheat 16-22 Mk11, during cold weather boiler heats both radiators and hot water, but in warmer weather, wont heat just hot water, (as Boiler doesn't come on as much I think) Has worked well in previous years, Problem seemed to start after a new gas valve was fitted. There doesn't seem to be any Summer / Winter switch.

Allan, September 2008

Hey,
Tony S you got that one spot on, the Header Tank was dry as a bone.
I freed up the ballcock valve, fingers crossed that has done the trick.
Well done Thanks' a million.
Allan.
P.S.
If you have a, or are considering getting a Apple Computer, and need any Advice/Help give me a call.

Allan, September 2008

Check the small header tank in the loft hasnt dried up as the ballvalve sticks.The heating will work ok because there is water still in the rads but the boiler will only stay on for seconds if the tank is dry.

Tony S, September 2008