Groaning pipes

It will certainly be the double check valves that are groaning - but I'm by no means convinced that you need them!

They are needed in situations where it is necessary to prevent contaminated water from entering the cold water system. For example, if you were filling a pond with a hose connected to an outside tap, and there was a mains water failure, pond water could get sucked back into the mains in the absence of a double check valve.

In the case of your bathroom, a lot depends on where the mixing is done. Taps which are capable of mixing a high and low pressure supply often have two independent paths right down to the discharge nozzle - so there's no chance of back-feeding stored hot water into the mains cold water system.

FWIW, I've just held a mirror under each of my mixer taps - and they *all* have concentric nozzles, with hot coming out down the middle, and cold round the outside.

You'd have to try really hard to contaminate the cold supply - maybe by having a hose fixed to the tap dangling into a bath of dirty water - and leaving the cold tap open during a mains failure. I don't think the risk of that justifies fitting double check valves - I certainly haven't!

Is it likely to be the valves themselves or something that's happenning as a result of them? And is there anything I can do (apart from removing them :-) ) to stop it?

I thought it was illegal not to when using mixer taps in this situation? I did go through the same thought process you're describing (I can't see how it would be possible to contaminate the mains when the cold pressure is so much higher than the hot), but I wanted to try and do things by the book as much as possible.

I don't think the taps I bought specified that they could be used with different pressures on the incoming supplies. I assumed that because the existing mixer taps were of the kind which mixes internally this wouldn't be too much of a problem. Maybe a mistake... I know the new bath one mixes internally, but I haven't looked closely at the basin one.

Cheers, Andy

It's the valves themselves. They have a little spring-loading valve inside which - at low flow rates - opens and closes at high frequency, causing a sound to be generated. I have one on an outside tap - which makes a noise like a swarm of bees in the utility room when it's in use.

Doubt it - apart from running the taps flat out.

As a matter of interest, does anyone else out there have double check valves fitted to *internal* mixing taps?

Do we have any resident experts on the legal requirements for them?

B*llocks. If I'd known they did that, I wouldn't have bothered.

All information on my options gratefully received.

Cheers for the replies so far.

I am not an expert (and not technically resident here either) but I do beleive that they are a requirement, purely on the grounds that it would be possible for water from your hot water supply to contaminate the mains if using a mixer tap that didn't have seperate outlets for hot and cold. This is probably partly the reason why most mixer taps now do have.