Thermostat and receiver may have lost pairing. Pair as per quick guide.
Boiler is still not working? Check;
*Receiver has power? (observe power LED).
*Receiver is in ON and AUTO mode position? Place in these positions.
*Receiver ON LED has activated?
Try receiver in ON and MANUAL – boiler should fire?
*If the answer to these questions is yes, you may have an electrical or boiler issue – call an installer to rectify.
The following advice is for competent electrical installers only (isolate electrical supply when necessary) and DO NOT attempt if not suitably qualified and competent;
Test the receiver installation / supply voltage etc using basic electrical checks;
Supply voltage is correct? If not, please rectify.
Test the volt free switch for continuity using a multi-meter.
Volt free switch has continuity?
If yes, receiver is not faulty. Possible external issue e.g. Zone valve microswitch.
If no, receiver relay may be faulty. Join Com and No terminals together – does boiler fire?
If no, receiver is not faulty.