Fixed it.
Replaced actuator on HW circuit, the mechanism to activate the microswitch wasn't working properly it was slipping.
Fingers crossed it stays fixed.
Thanks for the advice, saved me a few quid.
Agile
Few points:
This boiler has no fan?
The PCB just controls the pump overrun timing.
What do you consider pricey, I've found one for £30 at local plumbers merchant.
What model were you working on?
There are two 2 port valves.
I have also fairly recently(2-3 months ago) changed the synchron motors on both of these, following a problem that came up during the last gas safety cert. The engineer doing the safety cert phoned to say that the boiler would not switch off he had to switch off...
Just so I understand this correctly.
When the HW valve opens via the synchron motor the rotation of the valve switches the microswitch to tell the boiler to fire. This does happen i.e. the boiler does fire and stays on for a few mins, which would seem to suggest that the microswitch is working...
If the microswitch on the HW valve was broken would the valve still open and close via synchron motor? Because the motor does still open and closes the valve it just doesn't remain open long enough to heat the water.
Could this be a PCB fault?
Diverter valves working fine watched and heard them open and close for both central heating and HW. Also left open with manual lever boiler still switches off.
Have a problem with my Baxi Solo 2 40 RS boiler. Working fine for central heating but after firing up for a couple of minutes for the HW the boiler switches off before reaching water temperature. (Not a reset from overheating boiler just switches off).
I have changed the HW cylinder...