what can cause water surge from the boiler vent pipe that hangs over the boiler header tank?.
The filler valve from mains has been checked and that's ok shuts off at 2" below over flow but it appears the header tank is being topped up by surge from this pipe and then starts leaking out of overflow.

bob, October 2011

Thanks b it was for a family friend (Widow with disabled son) who's just been stitched up for £840 to change 8 standard manual rad valves close to £90 per hour . We were on holiday so we couldn't check prices. I would never be a rich plumber or heating engineer, I have principles, that chap didn't, time! at most 8hrs

bob, October 2011

? system fault or boiler stat overheating

b, October 2011