do I need check valves in my gravity-fed bathroom?

30 Aug 2007
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United Kingdom
In process of refitting bathroom. Cold water to bathroom is gravity fed from tank in loft. I assume same tank refills the hot water cylinder which is heated by an immersion heater (yes, an immersion). Hot water then runs to from cylinder to bathroom. We are planning a Bristan bath/shower mixer in the bathroom (the usual flexihose from tap to shower). bath shower mixer is two taps plus hose to shower type. The basin will be fed by a Bristan mixer tap. Flow of both hot and cold is to bath first, then basin, then cold to toilet feed.

I only thought I would need check valves if the system was unbalanced with mains fed cold and cylinder fed hot. Right? Wrong? If needed, which check valves???? and where?? Not much space to fit them in.
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Hi there,

If it is all definately gravity fed, then NO check valves requied as Syphonic action is not going to take place.

Only a couple of considerations to take into account.

1 : fit isolations valves to all water feeds (required under water regs)

2 : Make sure your tapes are suitable for gravity systems, most modern taps only work on properly on high pressure systems.

taps are suitable for gravity water pressure we have according to instructions

isolation valves will be fitted, thanks

I did see some stuff from WRAS regarding backflow contamination from flexible shower hoses i.e. to stop your shower head dipping into the bath, basin or toilet.

WRAS recommended Alternative Backflow Protection
There are several other ways to achieve adequate backflow protection, in addition to the use of a storage
cistern with air gap as described above (see the pdf).
Designing the bathroom so that the bath taps are at the opposite end of the bath from the WC allows a long
hose for the convenience of users but prevents it reaching the WC.
With existing layouts there are simple and cost effective methods to prevent the hose outlet reaching the WC:
(i) Fit a shorter hose so that it doesn’t reach the WC pan.
(ii) Fit a shower screen between the bath and WC, so the hose isn’t long enough to reach round it tothe WC.
(iii) Use a restraining ring or clip to fasten the hose to a shower rail or wall so that it cannot reach the WC.
The restraining ring or clip should be designed and fitted so that it is robust enough not to be easily
broken or have the hose removed from it.

this is all in a pdf file note compact bathrooms 11-06.pdf

If there were issues with the flexible shower hose reaching the basin I was going to use a restraining ring on the wall and will prob use a bath screen anyway. The shower head couldnt reach the loo whatever
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Yes I agree with & understand the water regs on backflow.

They only apply where a situation of syphonic backflow could occur.

If you bathroom taps / toilet are all gravity fed from tanks upstairs as you say. Backflow CANNOT happen.

Backflow only occurs when the is inadequate airgaps on taps. ie flexible showerhose left withits head underwater, where the cold supply is MAINS fed.

There is a burst in the cold mains in the street and the suction created sucks all the water from the bath.

As I said above, IF your bath outlets are all gravity fed then backflow CANNOT occur.


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