My Ravenheat 24T - LS80T combi bolier makes a noise similar to an egg timer (no puns please!) only when the central heating is called for.
When we just require hot water the bolier works fine and has done so for many years.
I have by passsed the digital timer but this noise still persist's, when we switch on the central heating!

If someone has any idea how i can locate and stop this noise it would be appreciated.

Paul Bales, February 2012