Non-return valves on thermostatic mixer ?

DriveSkill

Hi,

Are non-return valves generally part of a thermostatic mixer valve or fitted as an option?

Having some strange and annoying behaviour with our hot water :-) Bascially it appears like the hot water is coming from the tank through the mixer valve and OUT through the cold water INLET with the effect that we get some hot water coming through the cold taps in the bathroom and even into the cisterns sometimes. Once you draw off some it seems like the mains cold water pressure will eventually override so you will get cold then. However, we also get cold water feeding back into the top of the tank - if you feel the pipe coming of the tank it will be hot, then run the water for a minute of two and turn off and the pipe goes ice cold so the cold water has backfilled through the mixer it seems.

The end result is we are basically wasting a lot of hot water and when you come to have a shower you will sometimes get blasted with cold water even though the tank thermostat itself will show 60-70 degrees. System seems OK if you heat the water and use it quickly but its definitely an issue if other people start running taps or flushing toilets while you are showering.

So question really is should the thermostatic mixer by design block the hot flowing back through the cold inlet and vice versa or should there be non-return valves fitted either side of it to stop this happening. Do I have a dodgy valve ?

Thanks!

John.G

Is the HW supplied via a unvented HW cylinder viav the mains or is it from a combi boiler? or what.

Don't know if NRVs are installed in your mixer or not, you could have a dodgy valve but if the hot&cold pipes are easily accessible I would suggest installing NRV's as they are relatively cheap.

youtheman

Had a issue with a mixer valve fitted as part of a solar upgrade to my hot water system. The hot water was 'reverse' flowing back up the cold supply to the attic header tank. So I was getting hot water in my attic tank. Solution was simple, run the hot water pipe down to the floor of the hot press then up to the tank. Hot water 'rises', so by putting a u-bend in the system it will prevent reverse flow of hot water (simpler than a NRV, and no pressure drop either).

DriveSkill

Hi,

Sorry about the delay - the mixer valve is sitting on top of the hot water cylinder which is a closed system. Similar to the comment above it was actually put in as part of a Solar Panel upgrade a few years ago.

Definitely confirmed the water is flowing hot <--> cold through the valve. If we have hot water in the tank then as expected the pipe out of the top of the tank to the mixer will be warm to the touch and the cold feed to the valve will be cold. However, then if I turn on a COLD tap or flush a loo the hot side heats up more as it draws water from the tank and the cold side pipe also heats up so the water definitely coming out of the tank and back through the cold water system. Then once you shut off the tap the cold water flows back, cools the cold pipe but you can also feel it flowing through the hot pipe into the TOP of the tank so you then end up with 2 pipes which feel cold. Very obvious in this weather where the cold water is only <10 degrees.

I guess I really need a plumber to come look - I was just wondering if it was normal that water could flow from the hot to the cold side of those mixers.

DriveSkill

So I got a quote to replace the valve - no real breakdown of labour & parts apart from isolate the water, remove existing valve and supply and fit new one.

Total cost : €350

I know the labour costs are about €100 p/h and I was thinking this was a job that could be done within an hour so that mean parts are costing €250 ?? Alternatively its been quoted as a 2 hour job with €150 for parts.

Seems expensive or am I wrong ?

10-10-20

Best shop around, but it's a plumbers' market at this time due to the huge pressures on them, so prices are high.