On 2007-04-20 13:49:03 +0100, Norbet said:

Thanks to all who posted replies
I've just been home and have found the source of the problem. I forgot
to add that the doorbell is also wireless, but this hasn't worked for
ages.
When I got home this lunchtime I noticed the push button on the front
door had become stuck (so was constantly transmitting). Once the was
loosened - my boiler came on, I can now unlock & lock the car and the
wireless thermometer works again!!
Amazing to think that a doorbell of all things could cause such
problems!!!

Cheers
Norbet

.... and the cat can get in through its cat flap?

It's surprising that the doorbell push switch battery would have lasted
so long.