Shower Problem

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Bettypat | 10:17 Sun 20th Oct 2019 | Home & Garden
27 Answers
I have recently had my bathroom revamped and the bath taken out and a shower tray and shower run from my Worcester Bosh combiboiler. A seat has been put in as my sister cannot stand under the shower as she has severe balance problems. However, the water is running hot and cold and I do not know whether it is a shower problem or boiler problem. The supplier tells me that these bar showers fluctuate in temperature, but surely this cannot be right.


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We need to know the exact shower model
10:35 Sun 20th Oct 2019
No it can't be right and sounds like an attempt to brush you off. Did the shower supplier fit the shower?
Total BS, get the shower fitter back.
Did the shower have no temperature control ? Was the brief just to connect up two pipes ? Sounds like something the installer needs to fix, to me.
If it's not an independent electric shower then for it to run hot/cold the boiler must be cutting in and out. Suggests a fluctuation in water pressure. Slight chance your boiler may be switched to central heating priority instead of water heating?
Could you let us know the make and model of the shower.
davebro. It does not matter if the boiler is set for only central heating. A demand for hot water will fire the boiler up.

Doubt a water pressure is the problem. Just need to turn on a hot water tap and check that is OK.
ps. Not sure if it's the done thing to run a shower directly from a combi boiler! I may be wrong.
Is someone turning the hot water on somewhere else?
Probably not but an obvious thing to consider.
Unless the shower has its own thermostatic control there’s no way to guard against that.
AG. I have yet to see a shower without a temperature control.

There are some whereby the temperature is controlled by the rate of flow.
I am surprised that a shower has been installed which runs off a combi-boiler. There are three types of shower: gravity operated, power-assisted and power-heated. The first two types require both hot and cold supplies to have their own dedicated water feed. The last type takes a single feed and heats the water to the required temperature and my understanding, although I have no personal experience, is that it should be a cold, dedicated supply. If the water supply is shared with another outlet, such as a kitchen tap, the flow rate is bound to change as the other tap is used and so the temperature of the shower will vary.
Is it a shower fitted to the wall or a mixer tap type.
We need to know the exact shower model
Bar showers have separate feeds for hot and cold.
Unless you have a thermostatic control installed the water temperature is controlled only by the temperature setting in the boiler. And if the hot water is intercepted by usage somewhere else then the temperature will fluctuate as your installer said.
Unless the water to your kitchen hot tap is fluctuating in temperature when running at a constant rate, then I would suggest it is a fault in the shower control unit ; which I assume is under Guarantee.

Question Author
Thank you all for your answers. I have a maintenance contract for my
boiler with BG so I will get them to have a look at the boiler and eliminate that.
Our shower runs straight off our boiler bhg which is not a problem for us but then we are all fully mobile.
I don’t know if it’s possible to have a thermostat attached in retrospect. But sounds like the shower is behaving as it should, albeit it’s not what is wanted.
Question Author
The shower does have a temperature control. On my last boiler service I did mention that it was my intention to have a shower run from it and the gas engineer said it was no problem and there was provision for it to be fixed quite easily
ichkeria - thanks for that. As I said, I've got no personal experience of combi-boilers. When I installed my power shower (many years ago) I checked the regulations, which are primarily designed to stop the water suddenly getting hot and scalding someone. Imagine the situation where someone is having a shower and someone else turns on a cold tap, thus reducing the supply of cold water - the temperature suddenly goes up until the thermostat has time to react and someone gets scalded. That is why two-feed showers have to have a dedicated cold feed. Showers with a single feed should not suffer from this problem.
A combi boiler shower as a thermostatic control / temperature control. All you have to do to find out if your boiler is at fault, or your shower, is to turn on the hot tap at your sink in the bathroom, or elsewhere, if you are getting constant hot water from that tap, then your boiler is ok, and your shower is at fault. You need to do this first to find the problem.
There is some confusion here over types of showers.
Plenty of showers are made to connect directly to the hot feed (from boiler), and the cold main.
This is a "balanced" supply (both at mains pressure.)

the best ones are thermostatically controlled (cheaper ones are not - best to avoid these.)

Fluctuating temperature can be down to...

Others in the house drawing hot water at the same time. This can be overcome by fitting an "oversized" boiler. This can be made a whole lot worse in areas of very high mains pressure. Even though the supply is theoretically balanced, a combi boiler does exert a kind of strangling effect on hot pressure. If the cold is very high pressure, then imbalance can occur.

Or... faulty thermostatic cartridge within the shower body. It does happen. Anything new is more likely to fail early in its life rather than later. You don't give the make, but the best manufactures send their own appointed fitters to check out anything under guarantee.

Bar showers are no different from any other thermostatic shower. They should not fluctuate in use. :o)


I'll bet there's a bit of solder/debris stuck in the cartridge. Good fitters flush the system properly before fitting... some don't.

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