There was a previous long thread on this - asked to start explanation again - so new thread.
Initially had a total failure on boiler .. control board fuse kept blowing on power up, replaced the control board & harness, harness had to be changed as board had been superseded.
All OK for several weeks. (this may or may not be relevant)
Fault then started ... boiler would stop working, ... ignition lock out/over temperature LED (RED) is illuminated.
Simply turning boiler to off (via temp control knob) and then back on ... clears fault and it is then OK until next failure, which could be days.
I obtained another control board ... no difference.
The faults started getting more frequent ... sometimes a few times a week, on one occasion around 12 times in one day.
I removed water trap & cleaned, checked drain pipe is clear.
Reset electrode gap.
On advice I replaced flow temp thermistor .... and after changing that had no failures for at least 4 weeks.
It has now returned with a failure once or twice a week ... usually after being off over night.
Installation is Baxi connected to a Thermal store, so volume of store to cycle through (not just volume in a heating loop).
In the 28mm feeds to boiler there is a bypass loop, a pump on return and an anti-thermal syphon 2 port valve.
As this may not be easy to describe ... I have put a simplified sketch on line:
http://tinyurl.com/afx6ur
The fault always clears by switching off & on ... which would (to me) suggest that it is not a sticking pump or zone valve as if they had stuck, why would they have unstuck, every time when all I do is turn off & on (I may be wrong on this)
Initially had a total failure on boiler .. control board fuse kept blowing on power up, replaced the control board & harness, harness had to be changed as board had been superseded.
All OK for several weeks. (this may or may not be relevant)
Fault then started ... boiler would stop working, ... ignition lock out/over temperature LED (RED) is illuminated.
Simply turning boiler to off (via temp control knob) and then back on ... clears fault and it is then OK until next failure, which could be days.
I obtained another control board ... no difference.
The faults started getting more frequent ... sometimes a few times a week, on one occasion around 12 times in one day.
I removed water trap & cleaned, checked drain pipe is clear.
Reset electrode gap.
On advice I replaced flow temp thermistor .... and after changing that had no failures for at least 4 weeks.
It has now returned with a failure once or twice a week ... usually after being off over night.
Installation is Baxi connected to a Thermal store, so volume of store to cycle through (not just volume in a heating loop).
In the 28mm feeds to boiler there is a bypass loop, a pump on return and an anti-thermal syphon 2 port valve.
As this may not be easy to describe ... I have put a simplified sketch on line:
http://tinyurl.com/afx6ur
The fault always clears by switching off & on ... which would (to me) suggest that it is not a sticking pump or zone valve as if they had stuck, why would they have unstuck, every time when all I do is turn off & on (I may be wrong on this)