I have a problem with my hot water system/combi boiler. My CH works
fine and hot water did until yesterday. I now have to turn the hot
water taps on full to get the boiler to kick in and get hot water.
Having read similar pages on the internet, could it be a problem with
the diverter valve/diaphragm? My questions are... (1) do you think this
is the right diagnosis? (I get hot water easier when the CH is on,
which makes sense. Also the fact that this happened suddenly suggests
that the diagraphm may have perforated), (2) how difficult is it to
replace the valve/diaphragm/microswitch?, (3) should I try it myself or
get stung by a plumber?

I have booked a plumber (CORGI resistered) to come round this evening
to diagnose, but would like to save the call out charge and don't want
to waste his time and knowledge if then I decide to do the job myself.
If anyone could help that would be great.

Thanks

Roger