On Wed, 2 Dec 2009 21:23:51 +0000, geoff wrote:


My questions a

1. Are we right in suspecting the diaphragm is at fault here?

Almost certainly the diverter valve and yes, probably the diaphragm

Is there a small chance that lubricating it would help?

I have a 240, and the diverter valve pin that actuates the microswitch started
to stick. A drop of light lubricant (no, not WD-40!) sorted it, now going on for
a few years.


Personally, armed with the exact model and serial number (e.g. is it a
242E or 242EH?) I would email them and ask them which one (I would buy
the diaphragm kit as should include the seals etc. It's not something
you want to repeat next year because a seal has gone or something), then
the responsibility lies with them to get it right


3. Will we need the service manual in order to fix the problem or
should it be pretty obvious disassembly-wise to remove and replace?


No - the manual only goes as far as replacement of the diverter valve
IIRC

SO ...

You want to repair your diverter valve

Make drawings and photos at every stage. I can't emphasise how important
this is - there are so many things that could go one way or an other

Do it in one sitting then you have less time to forget

its much easier once you've done a few

Other than that, it's straightforward

Isolate the boiler, drain down, remove the diverter valve, mend and
replace

And you may need some stuff to descale the innards, depending on your water. And
gaskets for the stuff nearby. They will start to leak if disturbed when the
shops are closed...