New mixer 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

 

[GJS]

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!Kate

These things aren't necesarily related. Your new water supply is unlikely to have any effect on the flow or pressure to your own plumbing. They will just have rearranged the pipes and probably installed a meter.

Combi boilers generally have a low flow rate. Because they have to instantaneously heat the cold water as it passes through the boiler's heat exchanger it would take an enormous amount of energy to get fast flowing water hot enough. By the time the hot water reaches your shower, it is unlikely to be at a very high flow rate. It sounds like initially, when the flow rate was fine, that most of this was cold coming directly from the mains (hence the low temperature). Now, it seems, your plumber has restricted the mains cold supply to match the hot supply, thus increasing the temperature. This is borne out by the initial burst that you get. Pressure is building while the shower is off, probably in plastic pipes, then released when you turn the shower on, only to imediately fall back to the maximum flow that the boiler can provide.

The pressure gauge on the boiler refers to the water circulating around your radiators, I beleive 1 bar is normal and 2.4 sounds high. Check you boiler manual to see what the maximum pressure should be. This has nothing to do with the flow rate or pressure coming from your taps or shower.

I'm afraid I don't know of anything you can do about the current situation short of replacing the boiler for a larger model. In my opinion, combi boilers are a scurge and should be avoided. The only reason for their popularity is that they are easy and cheap to install.

 

[Goldspoon]

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.

Kate

Be careful here... my combi instructions say pressure between 1 bar and 2 bar and I generally hear that 1.5 is pretty much the norm. As GJS said though this pressure is only to do with the pressure of the water in the rads circuit.

 

[Goldspoon]

Kateharv... you may find this post slightly useful from a few days ago...

//www.diynot.com/forums/viewtopic.php?t=126673

I'm not sure that everybody dislikes combi boilers. We have a mixer shower and a combi and the shower is excellent

Also - surely if your plumber chose the correct shower for a combi boiler it should work straight out the box... he shouldn't need to add some water pressure reducing device (should he anybody?). Also I agree, yes you should be able to have a combi and a good showering experience - especially if you discussed requirements with heating engineer in advance of him fitting boiler... make a fuss.