Where does the PRV need to go?

[whitedot]

Hi there, hoping to find an answer on this as I've read varying opinions across the net.

We had a new bathroom installed earlier in the year and part of that is a Mira thermostatic shower fed from our Greenstar 30si combi boiler. We have powerful mains pressure and our builder installed a PRV (initially set to 1 bar) on the cold feed to the shower. This is behind the bath panel.

Everything was fine for a while (in fact I'm not sure what could have changed) but then it started fluctuating in temperature and more recently emitting a loud whine that can get really loud. Scared the **** out of me last night, it was that bad.

I've spoken to Mira today and they've told me the PRV is far too close to the shower and in fact it should be on the main as it comes into the house - ie before the boiler and everything else - set at 3 bar. They don't believe it's a problem with the shower itself because they had me test turning a tap on when it's whining and sure enough the noise stops instantly.

However my builder says he's fitted loads of showers and laughed off the idea of reducing the pressure to the whole house saying he's never done this. For now he's asked me to try increasing the setting on the PRV and see if it sorts the problem.

So my question is, who is right? Should the PRV be near my stop tap and reduce the pressure to the entire house, or is my current setup okay and simply needs adjusting?

 

[Dan Robinson]

Your builder is an a7se.

Simples.

 

[whitedot]

Your builder is an a7se.

Simples.

He's a spot on bloke to be fair and we're delighted with the bathroom in general. I assume you disagree with him on this issue though?

 

[sandybeach]

I always thought that the hot and cold should be of equal pressure, so I'd say Mira was right. Could you not fit another PRV on the hot supply to the shower?

 

[whitedot]

I always thought that the hot and cold should be of equal pressure, so I'd say Mira was right. Could you not fit another PRV on the hot supply to the shower?

Aye well it says in the installation manual for the shower that the pressures should be nominally equal, that's why I agreed with Mira initially too but I'm just a homeowner so I feel a bit daft arguing with someone who does it for a living.

Yeah I suppose another PRV is a possibility, but is there a reason for doing this rather than just moving the one I've already bought to the position Mira have said it should be at?

 

[GasBod]

which mira shower is it?

 

[whitedot]

which mira shower is it?

It's a Miniluxe ER.

 

[whitedot]

Just in relation to what I said about nothing changing, the only thing I can think of is that we had our boiler serviced after the bathroom was completed. No parts were replaced and the plumber actually said it was running perfectly well. Is there any way he could have upset something? Or is the noise and the fluctuating temperature from the shower purely down to this pressure business?

 

[Dan Robinson]

OP, I put it as simply as I could before.

builders as a rule, know naff all about plumbing. If you asked me about foundation footings you would get just as daft an answer as your builder gave you about pressure reducing valves and their application.

He might be a nice guy, but if he was spot on, he would have had a plumber to do the plumbing.


On my car club we have a guy going on and on how the manufacture can't find the fault on his car. Yet he freely admits to us (not the maker) that he has had the engine tuned. So his car is doing something it isn't supposed to and is using its resources in a way it was designed (by people with a lot more resources than the monkeys that played with it). Will be interesting to see what happens when the warranty bill is generated.

 

[whitedot]

Pretty sure he's a plumber by trade.

But anyway - PRV before the boiler for you?

 

[Dan Robinson]

Plumber? No he ain't.... Otherwise he would understand unbalanced supplies. He is a chancer with a nice attitude. We have one here that is a favourite poster boy for all sorts of media and manufactures. As it turns out - he isn't qualified to do squat. Doesn't stop the perception though. Also, next time you watch Rogue Traders or Watchdog... think about how matt Al-not-so-bright is looking a bit lonely. Perceptions mean squat. turns out that Portuguese prat was a benefits cheat... who'd have thought eh????


If you are going to balance the pressure - which is what you need to do - and you have high main pressure - which you apparently have - then you need to stick the prv somewhere before the hot and cold separate at the very least.

 

[whitedot]

Thanks for the reply.

Any other opinions? Builder is still suggesting I just need to up the PRV setting but wouldn't it just make more sense to have them equal pressures throughout the system? I'd rather not have to have to alter this again further down the line.

 

[HERTS P&D]

Take out the PRV leading to the shower and put it on the in-coming mains, set to 3 bar.

Andy

 

[whitedot]

I've bought a cheap pressure tester to put on the outside tap and see what pressure the mains (and therefore the hot water to the shower) is coming in at. What constitutes a relatively high pressure?

 

[denso13]

I've bought a cheap pressure tester to put on the outside tap and see what pressure the mains

No need, this is what you should do.

Take out the PRV leading to the shower and put it on the in-coming mains, set to 3 bar.