Plumbing

Combi Boiler temporarily firing when a cold tap is shut off

Anonymous user 09/03/2024 - 3.14 PM

Recently had our bathroom done and ever since whenever a cold tap is suddenly shut off, the boiler temporarily fires up (as if a hot water tap is being run). This is often accompanied by a low pitch whistle from the boiler. This pretty much always happens when the washing machine is on and the toilet has been flushed (and finished filling). It will occasionally happen if the cold tap in the kitchen sink is turned off (quickly). The installer has used all existing pipework so no dead-legs in the bathroom (that I know about), but not to say there aren't any elsewhere in the house (old house that used to use hot water tank in loft). Any ideas on what the cause might be and how I could potentially trace any unknown dead legs?