Problem with central heating system - it is working fine upstairs but not downstairs = boiler working fine, upstairs hard wired thermostat is working fine.

The downstairs room thermostat is wireless and is sending the signal to the receiver and this is working fine but then the receiver unit immediately switches itself off again.

This is a 2 circuit system and the ground floor circuit does not seem to operate properly. Suspect that it is the circuit valve? Maybe the wireless receiver box malfunctioning? How can I tell what's wrong and how can it be fixed?

Many thanks
Peter