It started with periodic lockouts which now happen daily. It didn't
always ignite after resetting so started to do it at the spur. Even
then it sometimes took a while to reset. This was accompanied by very
very hot water, way though the cylinder stat was set at 50 degrees.
The boiler did not respond to adjustments to the room thermostat also.

I have replaced PCB (with a new one!), air pressure switch, 3-port
motorised valve, room and cylinder stats.

I now have daily lockouts, the water is still piping hot and the
boiler now has a mind of its own. It comes on when the timer controls
indicate it shouldn't and goes off when it feels like it.

I was wondering if the behaviour of my boiler was/is consistent with a
dodgy temperature sensor and/or overheat stat?

Am I also right in thinking that if the DHW or CH are meant to be 'On'
through the timer than I should have a green light (either flashing or
permanent)on the boiler.

Thanks in advance

Dave