That pin is not making the switch.Can you see if the DHW microswitch behing the gas valve and ignition box is making, if it isnt you have a problem with diverter somewhere.
Has not fired up since changed the part, just makes a buzzing sound for a while which quietens after a minute or so.I'm not 100% if there is a manual o/ht stat on these, perhaps someone will know, is there not a white or black screw cap on front pannel nex to control knobs, with a flat slot in it? If yes, unscrew it and push the little button underneat it, that is your o/ht
Did it work when you 1st fired it back up, after changing part, was CH ok before?
Pump running as can hear the water moving in the radiators.
C/H was not working, H/W either.
Was left for quite a while with this spilt diaphragm in it, with only the H/W running when the C/H was on full blast.
I will look for this reset switch. Though I cannot see anything on the front.
If possible could, someone confirm which way round the new diaphragm should be. I might swap it round now just to test it. Then I will have to come back tomorrow to have another go at this.
Thanks again for your help folks.