Backflow from mixer taps - how would I know?

27 Jul 2013
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United Kingdom
Just a bit worried about how mixer taps have been installed by plumber in bathroom refurb. How would I know if I have a back-flow problem? My understanding from reading some other posts is that this would cause cold water to get into the hot system, to the hot water cylinder and thence from there warm water could then be vented into the cold storage tank in the loft? Is this right? If so I assume I'd have warm water coming out of a pipe in the cold storage tank in the loft - which pipe would this come from? Presumably it wouldn't be from the normal in-fill from the cold rising main - nothing can get back into that?

Also, assume I would expect water in the cold storage tank to feel warm?

Apologies for not being very knowledgeable on this. We have a standard system with hot water cylinder in airing cupboard and cold storage tank plus CH header tank in loft.
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Is the cold from the mains? If the cold was finding its way into the hot system you would find that, with hot and cold open at the mixer, the water would be cold, that is, no hot would be coming out. In most modern mixer taps the hot and cold are completely separate anyway. Which tap is it?
If your hot and cold are both tank no chance of backflow, however if the cold is mains pressure it could occur if you turn on both taps of a mixer and block off the outlet spout with your hand (a good way to clear air locks as it happens) then mains water could make it’s way up to the tank.

The main concern is if mains water is connected to tank water in a mixer tap or shower and the mains pipe is drained for any reason, in theory some water from the hot supply that has been standing in the tank could be siphoned back into the mains (drinking) water pipe work.

Ideally in that situation either the mixer should be a Bi-flow (what appears to be a single spout is in fact two separate pipes so the water only mixes after it leaves the spout) or check valves that only allow water to flow in one direction are fitted to the pipes.

What set up do you have?
Thanks Denso13. Tap is a Roper Rhodes Storm. Yes, the cold is mains fed, so the pressures of both are different, which I believe to be not good practice. Hot comes out fine at the moment although you do have to push the lever over further for it. I'm just worried that given the cold pressure it may force its way back into the hot system?
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Footprints, thanks. Just to confirm the set up with the Roper Rhodes Storm basin mixer is that its not bi-flow, so the hot and cold will mix in the tap. Also we have a bath mixer albeit that has two separate levers, but again the water will mix in the tap. No bi-flow and no check valves, cold under mains pressure and hot under gravity from tank. I'd just like to understand if this is a real problem I should raise with the installer or not. I've a mind to phone Roper Rhodes for their advice on the taps also. Looking on their web site, there is nothing on the installation instructions for the taps that mentions hot and cold having to be equal pressure, but would have assumed that's common sense.

Again though, what's the real practical risk of there being problems?
I don't think there is any risk of mains feeding up to the tank, unless you get your toe stuck in the spout and can't reach the taps to turn them of :LOL:

I guess that the local water company might have some concerns about contamination of the mains supply, but in practice the risk is really minimal a small amount of water sucked back from the spout into the cold supply is unlikely to cause a major health alert :rolleyes:

If the mains is drained for any repair you would normally run the tap for a short time to flush it out anyway.

Both my bathrooms have the same set up as you, I did put check valves in the ground floor one when I changed the taps but the upstairs one still doesn't have them, and so far nothing has gone pear shaped in the 6 years I have been here................................ ;)
Thanks for that Footprints, so you have same set up with mains cold and tank fed warm on a mixer like mine and no issues?
You should't have any issue in use but technically should have a check valves on the cold feeding the mixer. It's not to stop cold going up the hot but rather the hot water contaminating the mains in certain circumstances. Highly unlikely though.
Yup it all works fine, as said technically it's not 100% as the regs would like but in practice there are loads of systems out there the same and life goes on without something disastrous happening.

Idealy you can get some check valves fitted, but don't loose sleep over it :)

Thanks for your time on this today guys, much appreciated. I'll try and sleep soundly!

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