Bath mixer taps

Hi, I'm having problems with a bath mixer tap with shower attachment. The cold water is forcing the hot water back down the pipe when I switch it to the shower attachment- how can I stop this? I've got 15mm pipe feeding both hot and cold water and the cold water is feed from the rising main, I'm thinking of putting 22mm pipe on the cold feed and restricting the flow with a stop valve and also thinking of putting a non-return valve on the hot water feed - will this help?
MTIA
PhilB
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i`ve come across this a lot over the years and fiddling with the system as it stands usually does not cure the problem which is too much of a pressure difference in the hot and cold water supplies the only way to overcome this problem is to tank feed both supplies so they have equal pressure

cold
hot
with
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Thanks Jeff, I thought you may say something like that and not an easy job to do as the whole house has cold water coming from the rising main. The house (cottage) is very old so the only header tank we have is for the hot water/central heating. Phil

the
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What kind of valve? sounds like a bad dirverter or mixer.
1

cold
hot
with
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Hi Ned, The mixer is new and I've followed the makers directions and connected the hot and cold to the inlets they say. Phil

the
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Not sure I understand what kind of valve set-up you have. Is this shower attachment seperate from the shower head and tub spout?
I ask you agian what kind of valve??
From what you tell me so far i'd say you screwed up on your install. Go read the directions and find where you went wrong.

both
flow
hot
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For the benefit of amused/confused americans, you have a system that consists of mains pressure cold water and low pressure tank fed hot water. The mixer valve you have is not suitable for this as it appears not to be designed for such a pressure differential. You have various choices:
1. Fit a pressure balancing valve, which will choke off the cold to be the same pressure as the hot.
2. Tank feed the cold side.
3. Fit a single impellor shower pump to the hot supply.
4. Rip out the ancient gravity fed hot water system and replace with a proper mains pressure one, such as an unvented cylinder, heat bank or combi boiler.
5. Replace tap with one designed for unbalanced supplies.
6. Stick non-return valves on and make sure you only open the cold tap a tiny amount, or it prevents the hot coming out. (This is the option you are proposing).
Options 3 and 4 will provide the best overall solution, with rapid bath filling and excellent shower performance. (Except a combi would be slow on bath filling).
The other solutions basically mean bringing the cold supply to the lowest common demoninator, your low pressure hot supply. They will be slow to fill baths and provide very bad showers.
Christian.
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no wonder the teeth rot

combi
are
fill
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Hi Christian, Many thanks for your reply - sorry to have taken so long to respond but I don't get too much time to get on the ng.
Feeding the cold from the tank wouldn't be a too bigger job for me, finding the time to do it is the biggest problem. Fitting a pressure balancing valve seems a good alternative guess I can feel a trip to the plumbers merchant coming on over the Xmas.
Thanks again to you and the other responders to this thread.
Phil

combi
are
fill
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