Unvented cylinder - second shower low flow

Hi - please help if you can

A year ago I had a very old vented system replaced by a Worcester boiler and a non-megaflow unvented cylinder (I think its a Prostel). This has been fantastic - great shower in the main bathroom. Bath fills fast. Hot water at mains pressure/flow rate. Terrific.

A few months ago we had a loft conversion carried out and got the builders to install a simple Bathstore shower in the ensuite. No electric buttons etc, just a diverter valve to go to the rain head or the handheld shower attachment.

http://www.bathstore.com/products/metro-thermostatic-shower-valve-271.html

They took hot and cold pipes from the airing cupboard in the bathroom one floor down and routed these to the ensuite which is one floor up and about 4 metres along.

The issue is that the flow rate is disappointing in the new shower. it is quite a bit less than the main bathroom which surprises me as the height difference is not that great. I was expecting mains flow rate.

I have removed the two flow restrictors in each of the shower heads in the ensuite. This helped a bit but the two showers are very different in rate.

Secondly - if a bath is run downstairs and someone tries to have a shower upstairs, no water comes at all, in fact the pipes drain back I think because when the bath is complete and you try the taps upstairs again, you get all sorts of explosive ejection of air first!

Is there anything obvious I should check about this? Should the height make that much difference? Is this a known thing which simply cant be fixed? Are there any restrictors in the thermostatic valve panel itself?

Any suggestion would be much appreciated. Thanks!!

Wes

Assuming you have a basin in your new ensuite, have you any observations about this in terms of flow? Does this stop when the bath downstairs is running?

Is it just the hot or does the cold suffer the same symptoms?

Hi. Thanks for the response and sorry for the late reply....we have had a baby boy since your replies!

Anyway, to answer the questions, yes both tap and shower have the lower pressure and it affects both hot and cold.

The basin taps and the shower both stop if the bath is run downstairs.

Any advice or thoughts would be greatly appreciated.

Thanks!!!

OK, so it sounds like you have a pressure problem. The upstairs pressure will be less anyway, every 1m in height drops the pressure by 0.1bar.

I would expect that the mains pressure would have been checked as suitable prior to the unvented being installed. Was it like this when the guys installed the upstairs suite? if so they should have advised you and got to the bottom of it.

1st thing I would be doing is getting the system pressure tested.

Hi,

Wow I like leaving big gaps between replies here don't I? You wouldn't guess I have a 4 month old baby!

Anyway, yes the mains pressure was tested and all was supposedly well. I have also contacted Bathstore and they tell me the shower is rated for 1.5 bar and the shower valve for 0.1 bar so all should be fine there.

I have spoken to the plumber who installed the unvented system and he will visit in the next couple of days to try to help out. He says it may be that they (the plumbers who installed the pipes for the ensuite in the loft) haven't open the valves fully down by the cylinder on the stub pipework he left for them to use to take the pipes up into the loft. I hope this is the reason but I'm not sure that this would cause air to be sucked down into the pipes if the taps in both bathrooms are open.

Anyway. This is the story so far. any other thoughts welcome!

Wes

Sounds to me very much like your incoming mains is insufficient. Is your stopcock on full?

@muggles @Madrab @simond

Hi again! Its been a while but I thought I'd post an update on this.

The installer of the unvented system came around (nice guy - he really wanted to help) to investigate the issue. First off he tested the flow rate and the pressure. Both were off the scale - over 4 Bar and over 25 litres per minute on an outside tap which comes off the same water supply. We have great flow and pressure.

Then he looked at where the pipes that go up to the loft connect to the current pipework in the airing cupboard and said that it all looked fine. The hot comes from a T-join near the top of the cylinder and the cold comes from somewhere after the pressure regulator (if that's what its called).

The family (i.e. non-loft) bathroom has old taps which have a huge flow - again the flow was off the scale. The bath and basin fill up very quickly.

He simply cannot understand what the issue is. As a reminder, the taps are very disappointing up in the loft room and if the taps in the family bathroom are turned on then the loft taps and show actually draw back air into the pipes, which then gurgles out the next time you use the loft taps on their own. With the pressure and flow rate as I mention above, I was expeting that at the least I could have two showers running, even if they weren't at full whack. I have removed the flow restrictors in the shower heads.

Since the engineer left, I did a little test by putting my thumb over the bath tap fully open. Although the rate of flow is huge, it is very easy to stop with my thumb. This means flow is good but pressure could be poor.

I therefore have two questions:

- Can I get a pressure gauge which will work on a standard bath tap (without the screw join)
- Could it possibly be that the pressure regulator is either fitted incorrectly or malfunctions and is reducing the pressure far too much? If so, how can I check this please?

Any help with this would be hugely appreciated!!

Thank,
WesleyS

@chrishutt I'm hoping to loop you into this as your previous posts suggest you really know what you're talking about regarding pressure and flow and unvented systems. I hope you can help!

Cheers,
Wes

Wesley.... chrisshutt hasn't been on the site since 2009, I'm afraid the current responders will have to do, hopefully there is someone here these days that knows what they're talking about too

Has the Pressure Reducing Valve(PRV) been tested? I'd be tempted to check that as the 1st point of call and something your engineer should have checked? Does the PRV have a gauge or a slot for a gauge on it? If not then isolate the hot and cold feeds after the PRV and fit a test T to allow a gauge to be fitted. Yes you can get a gauge with a screw tighten rubber inlet but TBH they are never the best and always seem to leak.

Madrab said:

Wesley.... chrisshutt hasn't been on the site since 2009, I'm afraid the current responders will have to do, hopefully there is someone here these days that knows what they're talking about too

Has the Pressure Reducing Valve(PRV) been tested? I'd be tempted to check that as the 1st point of call and something your engineer should have checked? Does the PRV have a gauge or a slot for a gauge on it? If not then isolate the hot and cold feeds after the PRV and fit a test T to allow a gauge to be fitted. Yes you can get a gauge with a screw tighten rubber inlet but TBH they are never the best and always seem to leak.

Click to expand...

Hi @Madrab
Thanks very much for your response. I just added Chrishutt in case no one else saw the thread Of course I am certain that you guys know your stuff too. I just REALLY want to find out whats going on here.

When I'm home I'll take a photo of the PRV and post it here. Hopefully then you can tell me if I can add a gauge to it. I really hope so as fitting a test T may be a waste of money.

Thanks very much for your help on this.

W

wesleystrider said:

Since the engineer left, I did a little test by putting my thumb over the bath tap fully open. Although the rate of flow is huge, it is very easy to stop with my thumb. This means flow is good but pressure could be poor.

Click to expand...

That means there is effectively no pressure at all. You don't need to bother testing it with a pressure gauge - it will a fraction of 1 bar, the water is only flowing due to gravity.

Highly likely the PRV is defective.

flameport said:

wesleystrider said:

Since the engineer left, I did a little test by putting my thumb over the bath tap fully open. Although the rate of flow is huge, it is very easy to stop with my thumb. This means flow is good but pressure could be poor.

Click to expand...

That means there is effectively no pressure at all. You don't need to bother testing it with a pressure gauge - it will a fraction of 1 bar, the water is only flowing due to gravity.

Highly likely the PRV is defective.

Click to expand...

Well that's a pretty definitive, and I'd say exciting answer! Thanks for that. Quick check - when I say that I can stop that water coming out of the bath tap it does actually spray a little as I push with my thumb and it does take a bit of a press but I can stop it completely without very much force. Does that still sound about right for a duff PRV? I just checked and if I try to do the same with the hosepipe attached to the outside tap I can't stop the flow completely - even when pressing really hard there's always a tiny jet of water.

Should I therefore get a different plumber to come and swap the PRV or could I as a pretty competent DIYer do it myself? If it's not the PRV what else could it be? Debris somewhere?

Here it is in all its glory....



The top white bit of plastic has a sticker saying 3 Bar. The bottom is, I think, as safety valve stating 6 bar.

Anyway, why should I do now- first to confirm that the PRV is the problem and second how to fix it?!

Thanks!

That's your PRV with PRV (Pressure Reducing Valve and Pressure Relief valve) and is the inlet safety control group for your unvented cylinder. As such you need to have a G3 qualified Engineer look at this and replace if and as necessary and complete the benchmark.

Madrab said:

That's your PRV with PRV (Pressure Reducing Valve and Pressure Relief valve) and is the inlet safety control group for your unvented cylinder. As such you need to have a G3 qualified Engineer look at this and replace if and as necessary and complete the benchmark.

Click to expand...

Ok thanks for the info. Is there anything adjustable/cleanable behind those plastic caps (adjustable valve/cleanable filter etc)? Not that I would do it but wondering if the engineer might.