Problem - no hot water
have checked/replaced the following;
Gas pressure - ok
Water flow rate - ok
Boiler firing ok - ok
heating working - ok
have replaced both thermisters
have cleaned plate heat exchanger/ then replaced with new one (thinking it was problem)
Diverter valve working ok
Also, the pre-heat neon flashes when on, but does not turn off, ie pre-heat not working!?
Have had remote advice from engineer who is also lost for ideas.
Any help suggestions much appreciated.
Thanks in advance