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Hot Coming out of Cold tap With Vaillant Ecotec Plus 835 with a Salamander Homeboost

Postby dmedly » Wed Mar 20, 2019 3:00 pm


I have a Vaillant Ecotec Plus 835 with a Salamander Homeboost pump fitted to the mains supply underneath the boiler.

If I switch on the cold tap first I get cold and if I switch on the hot I get hot, the booster kicks in but doesn’t switch off, but..

If I switch on the hot tap first the booster fires; does not switch off when I close the tap, then if I open the cold tap hot water flows?

If I close one of the isolation valves the pump stops as expected, and if I switch the pump off completely the taps work correctly.

My gas engineer says it’s bizarre and can only suggest replacing the pump, Salamander say they don’t think there is anything wrong with the pump as it stops when the isolation valve is turned. And neither can understand why hot would come out of the cold!?

Any suggestions would be appreciated!

Thank you
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