Jaguar 28kw SHort burn / relight cycle

[ChrisB62]

Hi All
Any help appreciated.
Jaguar Combi boiler 28KVT J15
will sometimes work if isolated from mains for a few hours then switched on shortly after being powered up to mains.

It will then do it's initial burn until the demand temperature is exceeded, and cycle the flame out, as expected, but when the water temperature has dropped below the demand, the boiler goes into a short burn cycle, flame stays on for about 6 seconds, goes out for 5 seconds, then relights , stays on for 6 seconds and so on

There is no fault code displayed.
this fault is irrespective of demand source, ie DHW and CH

Thank you in advance
Chris

 

[twgas]

1st of all, check the system pressure, should be 1 - 1.5 bar

 

[ChrisB62]

Tried many fixes, boiler operated fine for one time only after each attempt, but burn durations kept shortening.

Bit the bullet, and replaced the Burner controller PCB assembly on the gas valve.
been fine for nearly a month now.

Thanks for the input.
Hopefully this is useful for someone with a similar malady