intermittant problem with digistat rf3 and gloworm combi

[markpad]

I have a Gloworm 3cxi and a Drayton Digistat RF3.

Recently an intermittent problem has started.

Sometimes, when the flame appears on the RF3, the boiler does not turn on. Sometimes, it works as it should.

I've taken the RF3 so it's close to the SCR and moved the temperature so that that there is a demand for heat. The red light flashes as it should, then the green light comes on on the SCR. Sometimes the boiler fires up, sometimes it doesn't.

It's completely baffling, as it has been working perfectly for over 4 years, and I haven't changed any settings recently. The DT20 programmer on the boiler is set to "On" and the hot water is working perfectly.

Interestingly, the overide button on the SCR doesn't work, and has never worked.

I have turned the power off to the Boiler/SCR, and it seems to work after it's initial set-up, then it goes back to working intermittently.

I haven't recommisioned the wireless unit to the SCR as it appears to be working OK.

It seems that sometimes, when the demand for heat is sent to the SCR, it doesn't pass the info to the boiler.

Any ideas?

Thanks for any help.