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Brian, Plumber
Category: Plumbing
Satisfied Customers: 864
Experience:  16 yrs. experience as plumber, including full bathroom and kitchen installations.
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Hi, I had a new Worcester Bosch Combi boiler fitted approx

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Hi, I had a new Worcester Bosch Combi boiler fitted approx 5 months ago (Oct 2012) as I was having a new bathroom fitted. The bathroom is finished but my shower runs hot then cold then warm then cold etc. It is an Ultra-group triple control concealed thermostatic shower valve with a rainshower head and a hand held head. The water pressure is pretty low when running either hot or cold (it does not change pressure at different temperatures unlike other taps in the house). The radiators and the rest of the taps in the house are absolutely fine and I can run a whole bath in hot water with no problems.
I have had an engineer from Ultra-group come and check all parts are correct, which he confimred they are and the shower is set up and working correctly, he even put a new thermostat in to double check that wasn't the problem. He said the problem is about water pressure and to get a heat engineer to check the boiler settings. An engineer from Help-Link came and checked the boiler who said it is definitely OK, he said it will be a problem with the shower, argh! I checked with the builder and plumbers who fitted the shower and they say they have installed it correctly following the Ultra-group instruction manual.
I even turned up the water pressure running into my house up my driveway, that did nothing.
Another suggestion was that the isolation valve to the shower may not be fully open but the plumber said he definately opened it. I can't check because it is under the tiles in the bathroom floor, the only way to get to it is to go through the ceiling in the kitchen, which I am prepared to do as I will be having a new kitchen at some point in the future.
I just want an answer as to what is wrong with it or if it is not fixable, PLEASE can someone help!?!
I can just about have a shower if I run the hot tap in the sink for a minute, turn it off then turn the shower on, get in the shower and it will run hot for 2 minutes then go cold. I then put the hot tap in the sink back on then back in the shower for 1 minute then it pretty much goes cold. There is no regulation of hot or cold in the shower, it is either really hot or cold and very little in between adjustment. It's driving me crazy and everyone keeps blaming eachother, no idea what to do next!
I would really appreciate any suggestions, many thanks, Francesca.

I've been working hard to find a Professional to assist you with your question, but sometimes finding the right Professional can take a little longer than expected.

I wonder whether you're ok with continuing to wait for an answer. If you are, please let me know and I will continue my search. If not, feel free to let me know and I will cancel this question for you.

Thank you!

Customer: replied 5 years ago.
Hello, that is fine to take more time, I realise it is a tricky question! Thank you, Francesca.
Hello Francesca:

Thank you for your continued patience. We will continue the search for a Professional for you.


Hi Francsca my name isXXXXX will need you to carry out two tests for me please. get a bucket and run a hot tap into it for 30 seconds and let me know how many litres you get. then turn your shower on to full heat and do the same.

Customer: replied 5 years ago.

Hello Brian,

I tried to reply a few days ago but do not think it sent. I ran the rainshower head hot for 30 secs which gave 1.75 litres of water. It also gave 1.75 litres of cold water running for 30 secs.

The hand held shower head gave 1.5 litres cold and 1.25 litres hot.

Thank you,


Ok Francesca that no problem.

My feelings are that you definitely have a flow problem. if you take the hand held for instance. You are getting 2.5 litres of Mixed hot and cold per minute. even on the showers hottest setting you get a mixed flow. so if we take an guess at 50/50 thats 1.25 hot per minute.

I don't think your boiler will function properly at this low flow rate. and you can test this by turning on your bath or basin tap to that level of flow so measure it roughly with a jug and see if the water in the tap goes hot and cold.

Your plumbers state they fitted it to the instruction manual but they need to be asked if they fitted full flow isolation valves, most inline isolation valves have a reduced flow the internal width of the valve is reduced to 10mm. this could be a reason for the problem.

Customer: replied 5 years ago.

Thank you very much, that is what we think may be the problem. Someone has suggested buying a push fit connection valve to replace the isolation valve so that more water can pass through the valve. We will have to cut a hole in the kitchen ceiling in order to get to the current isolation valve so before we hack into the ceiling, do you think this may solve the problem?

Thanks again,


just a standard compression coupling will replace the Iso valve. I am afraid I cant answer will it solve it. I can say it will help towards the flow. I think you are on a fine line between working and not because your water pressure is not great in general by the sound of it, I am sorry I cant help you with a positive yes it will fix it.
Brian, Plumber
Category: Plumbing
Satisfied Customers: 864
Experience: 16 yrs. experience as plumber, including full bathroom and kitchen installations.
Brian and other Plumbing Specialists are ready to help you
Customer: replied 5 years ago.
Thank you very much for your help. I very much appreciate it.