Drayton controller & boiler not communicating

[UmoGen]

We are experiencing an intermittent fault with our central heating

We have a Worcester Bosch Highflow 400 controlled by a Drayton RF2
(both around 10 years old)
The Drayton thermostat and receiver are communicating but the boiler is not responding

The heating light on the Drayton SCR will be on but the boiler demand light doesn't come on and we don't get any heating
(Hot water is unaffected)

Is there an easy way to confirm where the fault lies?
I am happy to replace the Drayton but don't want to do that then find the boiler is the problem

 

[bengasman]

Press the override on the receiver.

 

[UmoGen]

does it matter which override button?

 

[bengasman]

I think it is the bottom one, but try either, it won't hurt.

 

[UmoGen]

Thanks

I tried both buttons but no response
Went back to basics and turned the mains power off for 5 mins

Seems to be working fine again now

 

[UmoGen]

Alas the fix appears only temporary

CH has stopped twice today
Once came back on when I switched it off and on again via the thermostat

Second time this has not worked and neither has switching off the mains

How do I confirm the issue is the thermostat?