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Brian, Plumber
Category: UK Plumbing
Satisfied Customers: 840
Experience:  16 yrs. experience as plumber, including full bathroom and kitchen installations.
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I have only warm water at the shower but all the other taps

Customer Question

I have only warm water at the shower but all the other taps have hot water but if I turn the cold water on at the sink in the bathroom the shower gets hot. there is plenty of pressure in the hot shower tap Why
Submitted: 1 year ago.
Category: UK Plumbing
Expert:  Brian replied 1 year ago.

This sounds like you have an un balanced shower valve. Meaning the cold is fed from the main and the hot from a header tank. You dont state what led up to the problem occurring or if it has happened all the time.

Customer: replied 1 year ago.
There is no header tank. The problem appeared about 6 months ago. The shower has a hot water feed and a cold water feed. There is a diverter valve to divert the shower from the bath to the shower. To alter the water temperature you turn on either the hot water or cold water. I thought the cold water tap was leaking into the hot water but thinking about it. If the tap was leaking then water would run when the tap was turned off but this is not the case. The boiler supplies the central heating as well as the domestic hot water and there is no problems there. It is a mystery. I have spoken to a couple of local plumbers but they have no idea. As I have said all the other hot water taps and in the other shower everything works ok. The water pressure coming out of the hot water tap in the problem shower is good. If I want a hot shower I can turn on any cold water tap and hot water comes out of the problem tap. If you are American then a tap is a Faucet. The boiler is a gas combo boiler which does not need a header tank because it heats the water instantly.
Expert:  Brian replied 1 year ago.

Im Norfolk UK your fine. Ok so a combi boiler.

Heres some questions

Is this the only bath tap are all the other taps basin or kitchen sink or shower?

if the answer is yes

This is your plate heat exchanger, its unable to keep the FLOW of water hot . So when you turn on a cold tap it obviously decreases the flow and your plate heat exchanger can keep up.

The other taps and showers in your property use small bore pipe work, so although the pressure is good they don't use the flow that a bath tap does.

Hope this makes sense to you.

Customer: replied 1 year ago.
Hi Brian Yes. All the other taps are either in the bathroom sink or kitchen sink. In the other bathroom it is a shower only and this is fine and the hot water in the sink there is ok as well. Going back to the problem the water coming out of the shower and if I change it to the tap it as the same problem only luke warm water yet the water pressure is good at the tap/shower and as I have said earlier if I turn any cold water tap on then the shower water gets hot. There is 1 pipe coming from the boiler for the DHW which must go into a manifold which I can't see.
Bill (old retired diesel mechanic) so fairly handy
Expert:  Brian replied 1 year ago.

Hi Bill

Your cold water goes into a boiler and then into a plate heat exchanger, heat from the central heating water passes along copper plates which transfer the heat through the plate to the cold water, heating it up to serve your taps.

when the plates get scaled or dirty they dont transfer the heat as good.

So when your 22mm Bath taps are flat out your are passing more water through that exchanger than it can heat up.

When you turn on a cold tap in your house you obviously reduce the flow of water through the heat exchanger and it can then keep up.

To prove this for yourself turn on the hot bath tap full allow it to get warm and then turn it half off, you should find the water gets hotter.

Customer: replied 1 year ago.
Tried that but the water does not get any hotter. Tried turning on both the shower hot and the sink hot but then the water is only luke warm at either . turn off the shower hot and the sink hot tap gets hot.
Expert:  Brian replied 1 year ago.

I'm not explaning to you very well so I will opt out and see if anyone else can help you better.

Basically the more flow of hot water the less heat due to dirt in the plate heat exchanger.

Hope you get your problem resolved soon.

Best regards brian

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