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By camberley_stuck
We have an electric immersion heater (no central heating) and a few weeks ago a plumber installed a new shower and put the shower, basin & bath cold all on mains pressure.
We have mixer taps on everything.

We are now experiencing hot water being pushed back into the header (expansion) tank and causing water to leak outside via the outlet.

I suspect I need to fit non return valves but my question is … do I really have to fit 1 on the basin (hot) and 1 on the bath (hot) as this will be a nightmare.

I have noticed the immersion heater has 2 pipes at the top .. 1 going to the header (expansion) tank and another that feeds only the basin & bath hot tap

Can I not just put an inline Check valve here .. as its only feeding the 2 hot taps and water should only flow 1 way... it seems to me the same as putting a valve at the end of each tap.

The vent/expansion pipe will remain 'as is'

User avatar
best not to overcomplicate things first!

you will find that one of your mixer taps is faulty, the inner wall seperating the hot and cold flow inside the tap body has failed (cheap imported taps mainly). this causes main pressure pushing through the hot gravity feeds.

find and isolate this first as you re cross contaminating your wholesome water supply.
User avatar
camberley_stuck wrote:
December 8th, 2019, 8:06 pm
Thanks for this …
It was a cheap bathroom tap and I suspect this is there the problem started.

But, I can change the tap and just in case the next one goes faulty … will my suggestion be OK ?

not really, it will considerably reduce your hot flow being gravity fed. how do you make out its the hot pushing? it will be the cold mains with greater pressure to go uphil!

fix the fault dont cure the should have iso valves fitted, if not then call plumber back to do job properly. tthen turn a cold off at each mixer until you find the ttap thats causing it-bet its an older tap though!
By camberley_stuck
I think I have isolated it to the basin mixer tap as when this is even off there is water pushing up from the cold into the hot - of course this is the worst tap to change or mess with as the space is non existent.

The inner wall you mentioned .. is this the cartridge type thing inside the main tap ..
I ask this as I accidently ordered 2 taps when the bathroom was fitted and have seen a you tube video on how to change the cartridge ?

If so, this could be a quick win :)

I will also fit the check valve - I have a 22mm one that I will put on the hot water tank .. but you mentioned it will lose pressure.
There is not much pressure anyway at the moment .. and this is a "Tectite Sprint Double Check Valve DZR 22mm " from screwfix .. it looks the easiest to fit.
Will there be noticeable pressure loss ?

I did read somewhere that if I put a 22mm-15mm reducer on the pipe.. then buy a 15mm non return valve .. and then a 15mm to 22mm reducer this would help with the pressure loss that any NRV could do … is this right ?

.. I could always get a single check valve if you think that would be better ?

Thanks again for your help
User avatar
generally, its the brass water way inside the tap body that splits hot from cold.
the check valve could reduce to a dribble and prone to eventuall stick shut. Also, dont confuse pressure with flow, yours is gravity so it cant improve by reducing pipe bore.
if your cws tank is less than 2m above tap then dont do it.

Personally best advice is- get the plumber back to put it right as you might find yourself in a tizzle. last guy i had with your problem spent £600 for a £80 fix. ;)

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