Hot water backflow - non return valve?

mpet · 15 July 2019 at 7:49PM

Son has moved into new (not new build) house.

Bath has a mixer tap with shower head mounted on wall. Hot water is supplied by a combi boiler (old)with a pressurised red cylinder (no header tank). Cold water is from tank in the loft.
Not sure what make the mixer tap is.

The problem is when the shower is used, hot water is back flowing into the cold water tank in the loft, then running out of the overflow.

I think he will need to fit non return valve(s), but would they be needed on both hot and cold, or just hot? Also would they be fitted as near to the tap as possible.

Owain_Moneysaver · 16 July 2019 at 1:42AM

non-return valve on the cold, and a pressure reducing valve on the hot.

Or you could try a pressure balancing valve - includes check valves on the inputs which I think means non-return valves. This should enable both flows to be mixed properly but will reduce the pressure down to the header tank cold.

https://www.bes.co.uk/water-pressure-equalising-valve-16711

southcoastrgi · 17 July 2019 at 2:08AM

Strange that hot is pressurised but the cold is tank fed, rather than fitting check valves why can't the cold be fed from the mains as well & do away with the roof tank, it would only take a minimal amount of pipework in the roof.

Ruski · 17 July 2019 at 7:03AM

southcoastrgi wrote: »

Strange that hot is pressurised but the cold is tank fed, rather than fitting check valves why can't the cold be fed from the mains as well & do away with the roof tank, it would only take a minimal amount of pipework in the roof.

Southcosts's suggestion is the best solution by far:

If the hot is backflowing into the tank - a check valve would stop that, but would also stop cold betting to the shower. Sort out the cold feed as mains pressure as suggested.

HTH

Russ

mpet · 17 July 2019 at 1:35PM

Thanks for the suggestions- I can’t guess why the cold water tank was left - when we had our first combi boiler fitted, the cold water tank was removed.
As the last two posters have suggested - the easiest thing would be to change the cold feed to the mains - can’t believe I didn’t think of that!

Hot water backflow - non return valve?

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