New Shower = Hot water entering Cold Water Tank - Help!

[Richard76]

My System: A Cold Water Tank in the loft, with a smaller tank next to it for the central heating. The tank has the usual ball float controlling water coming from the mains, and two pipes at the bottom of the tank – one feeding cold water, and the other the hot water. We have a hot water cylinder in the airing cupboard, and a boiler downstairs.

The Problem: We had a shower room installed a few months ago downstairs near our boiler. It works fine, but whenever it is used hot water backs up into the hot water feed in the bottom of the Cold Water Tank. This causes the tank to overflow and water to pour out of the overflow pipe. Even though the shower is only on for 15-20 minutes this continues for several hours, gradually diminishing in pressure and then stopping.

This problem does not happen with the upstairs shower so I can only guess it is the new shower that is causing the problem. I’m reluctant to call the builder who installed the new shower as it appears he has caused the problem in the first place (at least I’m assuming he has).

Any ideas or help would be greatfully appreciated.

 

[weareleeds]

Why are you reluctant to get him back when he has clearly piped it up wrong somehow

 

[JohnD]

Does the shower receive its cold water at mains pressure, and its hot water at tank pressure?

You can test this by turning off your top-cock and seeing if the shower still has both hot and cold supplies.

 

[Symptoms]

How is the new shower supplied? Good practice might dictate its own hot supply from H/W cylinder & cold from loft tank - I bet your builder has hooked into the nearest h & c pipes (one probably the rising main) thus causing uneven pressures which might explain the h/w being 'pushed' up to the tank.

 

[Richard76]

Thanks for these replies.

"Does the shower receive its cold water at mains pressure, and its hot water at tank pressure" - Yes, the cold is definately mains pressure.

"I bet your builder has hooked into the nearest h & c pipes (one probably the rising main) thus causing uneven pressures which might explain the h/w being 'pushed' up to the tank." - Yes it does look like this is what has been done.

Is it possible to equalise the pressure?

 

[JohnD]

it is possible

but can you get a pipe up to take the cold water from the tank?

p.s. the person who fitted the shower like that is a buffoon.

 

[Richard76]

I've just called the builder who installed it, he is coming to look at it tomorrow. After I explained the problem on the phone to him, he said my hot water cylinder is the problem. I responded that I didn't think that was the case since the upstairs shower and bath are fine, and he said that the pressures were different between upstairs and down and the fact upstairs was fine did not matter. He said he would pop round tomorrow and investigate.

Could it be my hot water cylinder? It is quite old, but like I say there is no problem running hot water downstairs normally, or upstairs. It is purely the shower.

 

[JohnD]

If he installed an ordinary mixer shower with mains pressure cold and tank pressure hot, he is a buffoon. You can buy pressure compensators at additional cost when this layout is chosen and installed deliberately rather than carelessly or recklessly.

I think the pressure-reducing valve is about £35, and a special shower is a lot more.

I am no plumber but as far as I know professional plumbers are quite familiar with the problem.

If your upstairs shower is working OK I expect you will find it is supplied with cold water from the tank.

I had a pressure-reducing valve on the shower in my guest room, but it used to seize as not used regularly. I have an expensive special shower mixer now.