Combi comes on with cold water as well as hot

[superduffman123]

Hi,

We had a Valiant ecoTECplus 938 installed a couple of years ago. The past few months we've noticed it come on with the cold taps rather than just the hot. A plumber came to service it and said this is normal but we don't think it is + it's a waste of valuable gas. I've read up and think it might be a back pressure issue as the pipes do seem to slam when water is turned off. Any ideas or things to try would be greatly appreciated

 

[cjg]

get a shock arrestor fitted,

 

[Deleted member 120897]

Likely a dead leg on the system and no, it’s not normal. If you get the dead leg removed, this should solve your issue.

 

[superduffman123]

get a shock arrestor fitted,

Thanks, I installed Sioux Chief DW660-2J but no luck. Can you recommend a better alternative + would a check valve upstream of the shock arrestor be useful?

 

[Timmy D]

Turn off the cold water boiler feed at the valve under the boiler. Then run a hot tap and see if you still get water.

If it’s a new problem/not historic, it’s quite possible that a thermostatic cartridge has failed and is allowing a cross over.

Isolating the hot supply and still getting water out of the hot taps proves this. Then you’ve got to find it. Usually a shower valve.