We've got a Danfoss TS 715 controller running the pump on our CH system.
Recently it's been misbehaving - switch it on (override), and it turns on,
then a few seconds later the relay clicks off again (although the light
stays on).

Any ideas on what this might be? Knackered relay/other internals? Faulty
mains supply to the controller (though this seems unlikely)?

Is it a case of "get another one"?

cheers,
clive