Monodisc taps with unequal water pressure

[Roly]

We recently had a replacement bathroom fitted and the taps keep slowly dripping for several minutes after they're turned off.

The taps are of the single lever monodisc type, with a ceramic cartridge. The bathroom company has replaced the cartridge and now the taps themselves too, but nothing changes.

My understanding is that taps of this type need balanced water supplies, but we have the cold supply fed from the rising main and the hot is gravity fed from the loft tank. Clearly there is nothing like balanced pressure at the taps and you can see evidence of that by looking at the different flow rates for hot & cold water.

Could this imbalance be the explanation for the dripping ? What are the usual problems caused by unequal pressure ? The bathroom fitters are adamant that these taps are suitable and insist that they have never had a problem like this before, even with similar feed arrangements.

Obviously a solution is needed and one possible solution might be a pressure reduction valve. Is it likely to do the trick and would it be appropriate to have just one valve fitted in the pipe coming up to the bathroom rather than one PRV per tap ?

[Stewart]

I saw monobloc kitchen tap for sale in Lidyl at an exceptionaly good price and wanted to buy. My brother who is a plumber said not to do so as I would get a problm similar to what you are describing. He said that most of these taps are made for untits with combi boilers when the pressure of both hot and cold are the same. I have a mains fed cold supply to my sink but the hot is from a traditional hot water system (cistern in loft) so the pressures cannot match. The other problem is the very small bore of the pipe into the tap; this may not be a problem for you if you get a good enought flow from the hot on its own. In my bathroom I changed the flow from the mains to that of the roof cistern and then fitted a pressure activated pump so both hot and cold now match. It might work fitting a pressure reduction valve on the mains supply but I doubt it.

[dennis]

I thought it was illegal to fit a mixer where the hot and cold actually mixed before the outlet. None of the taps I have seen for sale have any common path shared by the hot and cold and the pressure difference is irrelevant.

[Andy Burns]

a one-way valve is recommended

Most of the newish ones I've seen *are* like that, I had to track down a Franke one that had a "coaxial" spout and mixed at the outlet.

[dennis]

Something must have changed then, I don't buy many mixer taps. ;-)

[Stephen Howard]

I've got a monoblock fitted in my kitchen - don't know what make it is ( picked it up at the local tip for a fiver ) but it's obviously a well-made bit of kit. Cold water is at mains pressure, hot is gravity fed - so there's a substantial difference in pressure, and I get no leaks at all. The unit has small bore tails, and separate paths down the outlet ( the cold water form a rather nice latticework effect ).

Regards,

[Garry]

Have you got a pair of filters in the feeds to the taps to keep out any small bits of crap in the water. Just wondered as i know if they start leeking there a bugger to fix.

Gaz

[John Evans]

Dennis is corrct - if the water mixes at the outlet the pressure won't make any difference. Ours has been working successfully for 10years, with tank hot and mains cold water. No drips or other turn off problems. Its the kitchen sink tap and is used frequently.

[crb]

I bought the Lidl one (=A315), as the =A3100+ "high quality" Pegler one that I bought was useless in terms of hot water flow (gravity fed from hot water cylinder) - and yes, I did check that there was no flow restrictor or mesh filter, and I changed the flexible hose for a wide- bore version).

The Lidl one works perfectly - and it does not drip.

CRB

[Stephen Howard]

Didn't notice any filters on mine - and given that the hot water comes via a Rayburn it's probably a problem waiting to happen!

Regards,

[Roly]

I gather that the dripping probably isn't caused by unbalanced water pressure. Why do the manufacturers insist that balanced supplies are used ?

What can be expected to happen if the supplies are unbalanced ? Is it merely the danger that water can cross-contiminate the other supply or is there another reason ?

[Quintar verbum]

replying to Roly, Quintar verbum wrote: In my case cold water from the mains pushed its way up the hot water pipe and caused the water level in my attic tanks to rise and overflow (via overflow pipe, but also cause minor internal leaks). It only happened when we were away for a few days. During daily use it never rose to a problem level, and hence was missed. Now I need to find a kitchen monobloc mixer that does not mix in the body of tap, but instead has separate paths as earlier poster described. I think they are less common now.