Whenever I flush the downstairs loo - after its finished refilling itself the boiler fires up in the same way that it would if I was turning on the hot tap!
its only for a few seconds but it definitely fires up...
I haven't noticed it before - the house is new to me but then whenever I have used the loo, before its had chance to fill back up again I've automatically used the hot tap on the sink so I suppose I wouldn't have noticed it, was only when I poured some dirty water down the loo that I actually noticed it fired up yesterday.
I've done some googling - apparently it might be caused by a dead leg in the system? I have just had a new sink put in the upstairs bathroom and the toilet is waiting to go in but the water feed pipe has been put there ready and has a cap on the end of it - would this possibly be the cause?
Did some experimenting in the downstairs bathroom and if I turn on the cold tap normally the boiler doesn't fire up - however if I turn it on in short sharp bursts it then fires up the boiler too....
Is there anything else it could be if the problem still exists after the upstairs toilet is connected?