shutting cold tap hard turns boiler on...why?

[bobb]

I have a WB 400RSF combi.

When I close my cold kitchen sink tap hard - it's a quarter turn ceramic type - it turns the boiler on.

My theory is that the water hammer caused by closing the tap sharply transmits through the water system and into the hot water side in the combi, and the shock wave flicks the flow switch on, thus setting off the hot water cycle.

Has anyone else experienced this and know how to cure it?

 

[Bahco]

Bobb

If it is water hammer, try turning your stop tap down a bit.

 

[ChrisR]

Only normally happens where there's air in the pipe, possibly in a dead-leg. Unless you have extremely high mains pressure like 8 bar, in which case fit a pressure reducer.

 

[corgigazza]

have of heard this happening before and was told fitting non-return valve on mains inlet to combi stopped it, phone up worcester technical to see if this is allowed as also small ex-vessel may also be required on the boiler side of NRV. let me know if it works