I have a 20 year old Glow Worm Space Saver 38 Boiler which runs fine most of the time but has started to occasionally suffer
with what sounds like the on/ off valve pulsing open and shut
(bangs while this is happening) - the flames pulse larger and smaller while this is going on. Only happens during heating
operation (not when heating water only). Can go for days without happening and then all of a sudden can start again.
Boiler has just been serviced - but happened before and after
service - would be grateful if any body has any ideas.

Bob, November 2006

I had similar problem but on hot water ony it turned out to be the thermostat mounted on the tank, replacement of which cured the problem.The type of thermostat uses abi-metalic strip which was not making aclean break.If you slowly turn down your room stat until it is just breaking you may hear it chatter.
hope this helps

rae, November 2006

YES, BOILER IS BEST PART OF 30 YRS OLD SO TIME TO CONSIDER A NEW ONE

BG MIKE, November 2006