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Discuss Advice needed. Converting gravity fed cold supply to mains fed to supply an electric shower? in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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6
I want to put in an electric shower in my downstairs cloakroom which currently has a gravity fed cold supply from the tank in the loft. The shower I am looking to install needs a mains fed cold supply which I could do by disconnecting this pipework from the gravity tank and connecting the cold mains feed, in the airing cupboard, to the cloakroom via the same pipe work. This cold gravity feed from the tank only supplies bathroom toilets and sinks and will not interfere with the heating system or bath fill which have their own separate cold gravity feeds. Doing it this way means that I wouldn't have to lift floors to run new pipework from the mains. Is their any reason why I couldn't or shouldn't do this?
 
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887
Bathroom toilets and basins would then have cold water at mains pressure. Assuming you have a hot water cylinder then the hot outlets would remain tank fed. You would thus have unbalanced supplies, which could give you quite severe problems with any mixer taps which were not dual flow.
You would also need to make sure that the WC inlet valves were appropriate for high pressure feeds.
 
Messages
6
Bathroom toilets and basins would then have cold water at mains pressure. Assuming you have a hot water cylinder then the hot outlets would remain tank fed. You would thus have unbalanced supplies, which could give you quite severe problems with any mixer taps which were not dual flow.
You would also need to make sure that the WC inlet valves were appropriate for high pressure feeds.
Hi, thanks for your prompt reply. I've checked taps and WC inlets and they are all suitable for high and low pressure systems (didn't say if they were dual flow). If the cold flow is too much for the hot supply would a flow regulator on cold side for the sink mixer taps be sufficient to balance the supplies?
 

king of pipes

Esteemed
Plumber
Gas Engineer
Messages
4,921
It's a risky thing to do id employ a plumber to guide you, cold water can quite easily push up the hot supply into your cold water storage tank causing it to overflow
 
Messages
887
1. If mixer taps mix the hot and cold in the body of the tap they are not dual flow. If the hot comes out of the centre of the spout and the cold comes out of the spout towards the outside, then they are dual flow taps. Because the hot and cold don't mix until they reach the end of the spout, neither can pressurise the other.
2. Its not the flow which causes the issue, its the pressure, although this can be manifested by reverse flow. So no, a flow regulator (valve) wouldn't help. You could in theory fit pressure regulators to reduce the pressure of cold to that of hot, but its not really the right solution.
3. I'm surprised you could determine the WC float valves were capable of accepting high or low pressures. Normally there is some sort of insert inside the valves, or a different coloured output nozzle, to determine whether the valve is suitable for high or low pressure.
 
Messages
6
1. If mixer taps mix the hot and cold in the body of the tap they are not dual flow. If the hot comes out of the centre of the spout and the cold comes out of the spout towards the outside, then they are dual flow taps. Because the hot and cold don't mix until they reach the end of the spout, neither can pressurise the other.
2. Its not the flow which causes the issue, its the pressure, although this can be manifested by reverse flow. So no, a flow regulator (valve) wouldn't help. You could in theory fit pressure regulators to reduce the pressure of cold to that of hot, but its not really the right solution.
3. I'm surprised you could determine the WC float valves were capable of accepting high or low pressures. Normally there is some sort of insert inside the valves, or a different coloured output nozzle, to determine whether the valve is suitable for high or low pressure.
Thanks once again for your advice,
2. would a non return valve in the hot supply prevent the cold reverse flowing through the hot supply, along with a pressure regulator in the cold supply?
If not would replacing the taps to dual flow solve the problem?

3. just going on the manufactures information from the web site with regards to accepting high and low pressure supply on the wc float valves
 

Ric2013

Plumber
Messages
2,958
This makes no sense to me. The OP seems to want to DIY the job, to (presumably) save money, which I can relate to. But is willing to replace mixer taps and even replace his hot water cylinder (an unvented cylinder is not something a DIYer can legally install).

It seems this is the result of the OP choosing the shower first and then considering how to make it work with the existing system, rather than approaching the matter the opposite way round.
 
Messages
6
This makes no sense to me. The OP seems to want to DIY the job, to (presumably) save money, which I can relate to. But is willing to replace mixer taps and even replace his hot water cylinder (an unvented cylinder is not something a DIYer can legally install).

It seems this is the result of the OP choosing the shower first and then considering how to make it work with the existing system, rather than approaching the matter the opposite way round.
See your point but I wouldn't dream of installing a unvented cylinder, I would leave that to the professionals.
Re-plumbing the house is not an option without ripping up laminate flooring from one end of the house to the other, this is why I'm trying to use existing pipework.
With regards to the shower, whichever electric shower system I choose throws up a problem. If it's gravity fed it has to have it's own supply direct from the tank. If it's cold water mains fed I either have to have a separate direct supply or re-plum pipework, but this causes back pressure problems with taps or wc etc. or I have a pumped supply but this still needs an independent feed.
A gravity fed hot & cold mixer shower would require nobody else turning on a tap or flushing the loo, so which ever way i go causes problems. Think I'll stick to my bath!
 

Ben-gee

Esteemed
Plumber
Messages
1,892
I think it’s a problem a plumber would solve for you, need eyes on though, I suspect there will be a point you can cut the gravity feed to the cloakroom so that the bathroom is unaffected.
Or an alternative pipework route, eg under kitchen units from sink pipework - then through wall etc etc.
We’re used to problem solving of this nature, I advise you to get someone round to have a look.
 

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