LVariable water pressure from mains, PRV on shower feed not performing as expected

[Randomdiyer]

Hi, looking for some advice on what to do about my variable water pressure.

I have recently had a new boiler fitted, it's a combi boiler fitted by British gas, the old boiler was a hot water tank and gravity feed system.

Once the new system was fitted I noticed that the hot water flow was surging, and when the flow surged the temperature dropped. British gas came out and fitted a PRV to the cold water inlet to the boiler. This evened out the flow and temperature of the hot water. All ok until I try and use the shower.

the shower continues to fluctuate in flow and temperature, I believe now because of the variable flow and pressure of the mains supply, which the cold feed for the shower comes off (this does not have the PRV upstream that British gas fitted).

after seeing the result of the PRV that British gas fitted, I thought I could fit the same thing on the cold water feed for the shower, and get the same pressure cold and hot water to the shower, however this is not working as expected. I installed the PRV into the cold water shower feed, and watched the pressure gauge on the valve, I noted the lowest pressure and adjusted the PRV down to this pressure, expecting the pressure then to remain solid at that pressure. Instead the pressure still drops off for a short period as before, but this time it's at a lower pressure, I repeated this until it was really low, and the pressure still drops off, I don't understand why.

The PRV in questions is a Honeywell 15mm.

any help or advice would be gratefully received.

thanks.

 

[chris watkins]

Re: LVariable water pressure from mains, PRV on shower feed not performing as expecte

Why are you messing around with it call BG back, it is their problem.

The PRV they installed to correct the problem should of been installed on the incoming mains supply to give you balanced hot & cold water pressure.

BTW welcome to forum.

 

[Sparkgap]

Re: LVariable water pressure from mains, PRV on shower feed not performing as expecte

Did you adjust the cold PRV with the shower running? Not knowing the layout would it be possible to have the cold feed to the shower off the boiler feed after the PRV, that way it will be at the same pressure (allowing for drop through the combi) instead of trying to balance two PRVs? Is it just pressure or are you getting temperature fluctuations on your shower when it happens?

 

[Randomdiyer]

Re: LVariable water pressure from mains, PRV on shower feed not performing as expecte

Hi Chris, as the hot water is constant pressure, flow, temperature BG are washing their hands of it.

Sparkgap, thanks for the response....yeah I adjusted the PRV whilst the shower was on. It would be possible to connect it up as suggested, but not without a lot of work, I'd like to avoid that if possible. The temperature of the shower does vary, I think this is because of the variation in the cold water flow/pressure.

 

[chris watkins]

Re: LVariable water pressure from mains, PRV on shower feed not performing as expecte

I forgot to ask is it a thermostatic shower ?

The domestic hot water produced by a combi boiler will almost certainly fluctuate in temperature this is because the only way it can try to maintain the temperature set on the boiler is to modulate the size of the flame or even turn it off if the temp rises to high but it is not that accurate a system, if you have a mixer valve where you are just blending hot & cold to achieve the desired showering temperature then you will feel it changing.

Installing a thermostatic shower should do the trick as it will adjust the blend automatically to maintain the correct outlet showering temperature.

 

[Unregistered]

Re: LVariable water pressure from mains, PRV on shower feed not performing as expecte

It is a thermostatic shower, a hansgrohe axor. I can't detect any fluctuation in flow or temperature of the hot water, but there is definitely a fluctuation in the cold. Hence why I think it's the fluctuating cold that is causing the shower problem.