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
Without seeing the boiler, if the hot water wasnt working on a Baxi 105e I would say check pressure differential valve, but with the Baxi instant you should still get abit hot water just off the pre-heat.
Problem solved. I have replaced the 3 way valve assembly and the hot water divert valve part above it, eureka!
Even after cleaning old parts there still must have been a fault as it was sending hot water down the heating flow pipe in DHW mode rather than through the plate heat exchanger. I hope I'm making sense.
This means I now have a used (but working fine, and cleaned out) heat plate exchanger going for a small price!