New mixer shower and combi boiler - shower losing power

[kateharv]

We have recently had our old cylinder heater and boiler replaced with a glow-worm combi boiler. This has been fitted in our old cylinder cupboard behind our bath and we have had a new thermostatic mixer shower fitted to run off this. Before these were fitted we also had a new water system fitted by the water company as we used to be on a shared system.

Our installer had the boiler and shower fitted by Tuesday evening and the shower pressure was fine, although the shower didn’t get very hot even with the temperature knob completely on. He needed to come back on Wednesday to fit the thermostat etc and I mentioned the heat issue to him.

When we came home from work yesterday, the heat of the shower is better but the power has gone a bit weird. When you turn the shower on the power is fine but then it drops significantly almost straight away.

We noticed the pressure on the display on the boiler was 0.9bar and it says in the manual if it’s less than 1.0bar to add pressure. So we did this and the pressure is now at 2.4bar but the shower is not working any better.

I was under the impression that if we had a new water system, new combi boiler and new shower fitted we would have a pretty good shower!

I was wondering if anyone had any idea what the problem might be? I don’t really want to have to get my plumber back out if it’s a relatively simple thing to fix…

Thanks for your advice

Kate

[John A]

First of all drop the pressure on your boiler to 1.5 bar maximum when it is cold by bleeding one of the radiators until enough water has passed to lower it. Upping the pressure on your boiler will have no bearing at all with the pressure on your shower.

The problem with your shower sounds to me as if the hot and cold pipes have been conneced the wrong way round, hot to cold and cold to hot. Check this first. Sometimes the manufacturers stick labels on the showers to say which is which but they do occassionaly make mistakes.

It would also help to have pressure reducing valves on the hot & cold pipes to equalise the pressure. Some of the more expensive showers incorporate this already

[chris_on_tour2002]

your system pressure should never be more than 1 bar (1.5 bar absolute max) when cold - the additional capacity is to allow for expansion when it is running hot and for safety - the system has been designed to operate well WITHIN its limits, not on the edge of its limits. cranking up the pressure that high will only cause the system to lose water via the pressure relief valve or, much worse, through a leak at a weak joint that suddenly isn't up to the additional strains caused by the higher pressure.

and, as john A says, it will have absolutely no effect on the water pressure coming out of your taps anyway. the two are completely separate.

[rosebery]

How recent is recent?

I think you SHOULD get him back if it's as recent as your post implies. He has an obligation to fix it!

Additionally if you get a serious problem crop up which you would want him to fix and he sees that someone else has been working on the installation he would be within his rights to charge you for the second visit because "someone else has been interfering with this and it's not therefore my fault"

Cheers

[chris_on_tour2002]

check that your shower is compatible for use on a combi system. not all of them are due to the potential pressure difference between hot and cold.

[rosebery]

"chris_on_tour2002" Check that your shower is compatible for use on a combi system. not all of them are due to the potential pressure difference between hot and cold."

With both hot and cold at mains pressure? Of course if there's a flow restrictor on the HX and the flow valve isn't fully open the pressure could well be different.

Nevertheless the spec of the shower is still the installers problem if he supplied and fitted it.

Whatever, I think you SHOULD get him back in!

Cheers

[bullydozzer]

hi i know its an old thread but i had the same problem it was the boiler
the flow rate litres per minuite wasnt high enough on the boiler to cope all the plumber has done in your case is turn down your cold feed to the boiler thus making it hotter water but with less pressure