Sort out my friend's lousy shower

As far as I am aware you should never mix tank and mains pressure at a shower. Unless there is a non-return valve on the cold this looks a very dodgy set up because you are connecting mains pressure to tank pressure through the shower head.

I assume that there is still a hot water tank, otherwise why the header tank in the loft? That is, the boiler is working as both a combi (directly heating mains hot) and a system boiler (heating some kind of hot water store).

Two alternative solutions; install a pump to take hot water from the tank and cold water from the loft, or plumb in mains cold to the shower.

In either case the shower should be a high pressure model for mains pressure as opposed to a low pressure model for gravity fed.

It does sound like a plumbing bodge from what you report.

Cheers

Dave R

As a matter of interest, how does the flow of hot and cold compare into the bath?

Low pressure water from a header tank requires special fittings to have a chance of working reasonably well, but most fittings on the market are made abroad, and designed for high pressure. And even then expect reasonably matched pressure from hot and cold.

One way round would be to fit a pump on the cold water side.

Buy a new pressure balancing mixer? Fit a PRV on the cold side? Fit a pump and PRV? Go pressurised hot water.

PRV is cheapest if they get enough flow from the hot.

He said the hot water is pressurised so I assume it's from a combination boiler. It's the cold that's still via a header tank, so isn't the solution to connect the shower cold feed to the rising main, along with everything else, and decommission the tank and cash in the old redundant cylinder that's presumably still there?

I'm not there now but I assume that the bath tap is one from the days when there was a hot water tank in the loft so the hot and cold would have been gravity fed.

The tap is old and I don't think there is anything within the tap to cater for anything other than a flow of gravity fed so unless a PVR is fitted to the hot water side which is mains pressure, or the cold is upped to mains pressure as per my suggestion there will be an imbalance.

What is wrong with connecting the mains pressure inlet at the tank to the bath cold, rather than fit a pump?

No idea even if there is a hot water tank in the attic. The boiler provides mains pressure hot water. Cold water is from the tank in the attic.

The latter is what I was proposing by connecting the inlet of the water tank which is mains to the tap cold, bypassing the cold water tank.

He has something like

but a genuine old version with a knob to lift up to divert the water into the shower. The knob only stays up if there is pressure so the cold water alone doesn't hold it.

Well whoever installed the combi-boiler 11yrs ago surely could have sorted it without much more effort, but if my friend didn't ask then maybe they just took the old out and put the new in?

If you have sufficient flow and pressure, possibly. But when turning on another tap anywhere in the house effects the shower, not so sure.

That's what happens when you don't read the question. So put the PVR on the hot side if there is enough flow from the cold or as you say connect the cold to the mains which should be easy to do next to the tank.

It is unlikely that there would have been a hot water tank in the loft.

Usually a system is all mains pressure (as with a combi boiler) or (almost) all gravity.

With a gravity system you have a cold water header tank in the loft and then a hot water copper cylinder in an airing cupboard, often close to or in the bathroom. Hot water is pre heated and then when the hot tap is turned on cold water from the loft flows into the bottom of the hot water cylinder and forces hot out of the top and through the hot tap.

One important thing is to have a mains cold water tap for drinking water as cold water in the loft tank can sit there for a while and can also get contaminated by vermin.

What you describe is not a normal system and sounds suspiciously like a cowboy installation. Usually if a hot water cylinder is removed and a combi boiler fitted then all the cold water is converted to mains pressure and the header tank is removed.

The only usual reason for a header tank in the loft is to provide a head of water for the hot water tank. In that case the cold feed to a mixer tap should also be from the header tank.

Your original suggestion that mains pressure should be connected to the cold side of the shower was sensible; however we are asking further questions to try and establish if this is an unusual but generally logical set up.

For example there may still be a hot water cylinder which supplies all the hot taps apart from the shower, and the combi boiler may have a circuit on the central heating side which heats both the radiators and the hot water cylinder.

The second point being made is that if the shower mixer is a hang over from a low pressure gravity feed system then it may be unsuitable for a mains pressure system even when both hot and cold feeds are at mains pressure.

If you have a mains pressure combi boiler there is a limit to the amount of hot water it can supply by instantaneously heating the incoming cold water and the shower has to be designed to produce a good high pressure spray at this flow rate. It has to work at a low flow rate and a high pressure.

Low pressure tank fed showers tend to pass a lot more water through at a much lower pressure to provide a satisfying shower. If you use a low pressure shower mixer with a mains pressure supply you may never get a decent shower.

From online specifications the boiler should provide a hot water flow of between 10 and 13 litres per minute (assuming enough pressure and flow from the incoming main). If the shower is not designed to operate at that flow rate then you are wasting your time. Connect the cold mains to the input to the shower mixer to match the hot mains, but be prepared to also fit a new mixer designed to work with a combi boiler.

I do have a (possibly unworthy) suspicion that if this shower has been endured for so long there may be a reason why it hasn't been fixed. Perhaps a reluctance to spend money?

TL;DR - connect mains cold to the bath, and fit a new mixer.

Cheers

Dave R

That's true, it's not perfect, but it's how the majority of thermostatic showers in the UK are plumbed, and it must be miles better than HP hot + LP cold.

I wouldn't want a water pipe making a dog-leg detour through my cold loft space when there is no longer any reason to do so.

Cowboy installation? Maybe.

It took me quite a while to get my head round the water supply in our bungalow. It has a standard (non-combi) gas boiler, and the usual tanks in the loft - cold water and expansion. There was also a double-sized hot water cylinder.

There are four showers! One is an instant electric one in one bedroom. The master bedroom has an en-suite, and the main bathroom has a shower cubicle, and shower attachment on the bath taps (of the sort shown in the previous post link). The en-suite and bathroom cubicle showers have pumps (hence the need for a double-sized HW cylinder). The HW and CW supply to the shower pumps is taken from the CW tank and HW cylinder. So far so good. It is when I started looking at the CW supply to the rest of the bathroom and en-suite fittings that it became interesting.

I found the bath shower attachment very sensitive to the CW tap setting. With the HW tap fully on, slightly opening the CW tap led to a cold shower only. And if left for a few minutes, the HW didn't immediately reappear when the CW was turned off. It was obvious that CW was being forced back into the HW system. It then became clear why I had had to turn off the isolator valve almost completely for the CW supply to the bath and en-suite basins. It was very easy to open the quarter-turn taps fully and get drenched with splashback from the basin!

Effectively, only the showers were fed (via the pumps) from the CW tank. All other CW supply, to the bath, basins, and cisterns, was at mains pressure. When I mentioned this to our plumber one time, he said that it was unusual, but he had seen it occasional.

Its the normal way to do water in the Midlands and in many other parts of the UK where there is good mains pressure.

Its also the best way as it is safer than having tanks of stagnant water available from taps.

It does mean you need to run the cold for mixers from the header tank if you have a conventional (old?) system.

There was in my existing (1968) bungalow but not in my previous and older 2 storey house where the header tank sat above the hot water cylinder in the bathroom.

I don't have enough experience to say "usually".

Or variations of the above it would seem.

Agreed, I'm not convinced my friend has this, but he's still alive after 35yrs of living there.

An older (presumably non-combi and less efficient) boiler had been fitted and replaced 7 yrs ago.

Well yes that is exacerbating the problem. I don't think any cold water is actually reaching the shower head, it is just going to get pushed back up to that height by the mains pressure hot.

Fair enough - I can't pop up now to check.

Almost certainly. The hot water tap in the adjacent sink drips, possibly for that reason.

There is plenty of hot water gushing out and it's far too hot for a shower.

I had hoped that we could simply turn the hot water temperature down (we have a separate control on our boiler) but despite showing a separate control in the on-line manual it would seem that the hot water temp is fixed at 55deg.

Combination of ignorance and lack of good advice I suspect.

Certainly one option, or PVR as elsewhere suggested. I've recommended he try and find a decent plumber but we are talking Walthamstow and I'm used to East Midland prices.

There are all sorts of variations by area. In London, it was common to have everything from the header tank except the kitchen cold water. I've even seen some older houses with tank cold water to the kitchen too - so three taps. Stored hot water produced by some form of back boiler.

But that dated back to houses built with a single bathroom with just a bath.

I've kept things that way here. Despite having an additional bathroom with a shower rather than bath.

Only modification is to have mains cold water to bathroom basin taps for teeth cleaning, etc.

I think it used to be part of then Scottish Water Regs.

That may help, but alone but may not solve all the problems.

You really need mains (or similar) pressure feed on both hot and cold, and then either a thermostatic shower or at least a pressure balanced one.

If there is a separate identifiable cold feed to the bath, then by all means connect it to the cold main.

As to solving other problems - much depends on what the actual issues are - there are a number of ways that combi fed showers can not perform to expectations.

From my own experience.

Temporary cure - use a plastic peg with a bit carved out to fit the spindle to keep it up.

Permanent cure - replace the tap / shower unit with one that has a plunger that you press down for the shower - Wickes do them.

Check the cold water feed pipe between the bath cold tap and the tank for an isolation or gate valve and make sure that it is fully open.

Look in the tank where the cold feed pipe emerges - is anything stuck in it like loft insulation reducing the feed? I've had that happen and had to blow it out by sending mains pressure water up the pipe.

Is there an isolation or gate valve on the hot water pipe to the bath? If so partially close it to reduce the flow to be similar to that of the cold water or fit one.

Even without that, provided the taps are as shown in the link you gave ie not a ceramic disk but the older type with a washer that screws down requiring several turns of the tap to turn it off, provided the washer isn't badly worn, you should be able to turn it on slightly to give a slow flow of hot water to match that of the cold tap fully open. Then use the peg to keep the shower working. This will allow a slow shower of the correct temperature (provided no one else uses a tap or tioilet fed from the same cold water pipe).

If the shower hose is an old coiled metal type then the narrow plastic tube inside is likely to be distorted and reducing the flow - replace it with a new wider reinforced plastic one.

Descale the shower head or replace it.

If they still wqant a faster flow and don't want the disruption of replumbing then do what I did fit a Triton T40i booster shower pump. This is just a pump (not a heater) which only takes 90W maximum so is easy to fit - I drilled through to the next room and either wired in a new isolation socket or temporarily just plugged into a socket. The shower connector from the taps is connected by a hose to the inlet and then the shower connected to the outlet. With it turned off and the water running into the bath, turn the cold tap on full, adjust the temperature by slighty turning on the hot tap, pull up the plunger and fix with the peg, once some water is coming from the shower head turn on the pump. You will then get a good flow of water at the right temperature. NB To avoid damage the pump must be turned off before turning off the taps. - that worked until we had time for the disruption of plumbing work.

Good luck

Alan