**** Update to this thread ******
Got someone from this forum to do work on this boiler.
His effort and commitment can't be faulted dealing with my crap heating system and I appreciate he helped me out valiently at short notice.
Work Done:
1. diverter cleaned; water system drained for this;
2. heat sensor swapped out (sorry, forget exact name).
after this hot water stopped completely / heating was erractic (PANIC STATIONS).
Looked like pilot light sensor firing up but not staying on.
Next Day
1. electrics fully checked (passed)
2. New (2nd ) PCB fitted.
This restored heating and hot water but still have to halve cold water pressure to get hot water and then temp only goes to low 40s.
So have heating and limited hot water still.
Bill now over £1000;
Plumber has reccommended a proper service and also suggested enlarging the gas supply rate as it seems to be operating lower than optiumum.
Also maybe replace both shower valves as they could be contributuinbg to poor hot water flow.
So the saga continues and im finding nearest cliff to jump off.