2 years ago we had our boiler replaced with a Vaillant Combi (can't remember the model number) and Towerstat RF thermostat. On the whole they seem to work fine together. However, yesterday I came home to discover the room temperature was 24C with the boiler still firing despite the thermostat being set with a daytime temperature of 21C and also "claiming" that the boiler was currently off. When I checked the receiver next to the boiler the green LED was lit, which I believe means the receiver thinks the boiler is on - In other words the receiver and thermostat were out of sync. The last time I saw this discrepency between the RF thermostat and the receiver was last Winter (2009) and I traced the problem to a low battery in the thermostat. However, this time round the battery level is ok (~50%). Also, the thermostat is <10m away from the boiler (albeit there are a couple of walls inbetween) so I would have though the radio signal wouldn't get jammed. What I don't understand is why the two devices don't "handshake"; i.e. so that the thermostat sends a signal "turn off boiler" and then waits for an *acknowledgement* from the receiver to say "this has been done". Has anyone else encountered this problem or am I missing something obvious?