My boiler makes a loud squealing sound when the central heating is on and we use the hot water. This used to be able to be stopped when we put the cold tap on, but this is not the case any more. I have been told that this is likely to be a faulty ignition switch but whenevere I have had a gas fitter out (3 in total), none of them are familiar with the boiler and know what to do , and are therefore not willing to look at it. Please please please can anyone help.

Stephanie, January 2007

The noise is caused by faulty O rings in the diverter valve. these will have swollen and allow water to pass between the Oring and the brass bush they are fitted to.
There are two causes of the O rings swelling 1, an inhibiter called Everrad 2, the boiler repeatedly "short cycling" (usually firing up when all the radiator valves are closed).
There is adiverter service kit part number 6281540 which contains all the partts required to repair the diverter valve.
sime can be contacted on enquiries@sime.ltd.uk

terry brow, August 2007

there is a by pass which you can adjust it is located at the left hand side of the pump just twist it and it will stop

ricky, July 2007

i wouldn't say its got anything to do with ignition switch, the boiler is running. hard to guess without hearing.

hi-spec plumbing, January 2007