Adjusting PRV

For some reason unknown to me, our house has two incoming rising mains, bot h with internal stopcocks rising up from the solid floor.

Our combi boiler is attached to one source, as are the majority of our cold water taps, and the other main supplies a handful of other cold outlets.

Local pressure is reasonably high (around 5bar I think) so both rising main s have PRVs attached.

The PRV attached to the "cold water only" main was installed to allow the t hermostatic mixing bar shower to regulate the temperature properly, as it s eemed that the pressure of the cold supply was overwhelming the hot.

Over the last few weeks I've been unable to control the temperature of the mixer shower, such that it is always at a temperature just below ideal - no matter what I do to the temperature adjustment (including removing the hea d and adjusting it) it comes out at the same temperature. To make my showe rs more enjoyable I have taken to leaving a cold tap running (supplied from the same main as the cold feeding the shower), which works (just) and rais es the temperature to a reasonable one.

At the weekend I thought I'd see if I could make some fine adjustments to t he PRV to resolve this.

It is a bog standard COMAP device (same as

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which has a black cap and a screw in the top.

I presume that the adjustment that I should do is to twist the screw in the top? However, doing this appears to have no impact on the gauge reading.

I was wondering if the PRV had failed, but it occured to me this morning (w hen the shower I had was nearly freezing because I clearly had had some "im pact"!) that waiting for the pressure gauge to move whilst there was no col d water flow taking place was probably misguided.

Is this the case - do you "set" the pressure on a PRV only whilst the water is in flow (and if so, how much flow? Full taps open, or would less than this suffice?) And am I barking up the wrong tree trying to adjust the pre ssure on the cold side to have an impact on the shower temp?

(Sorry, this seems like a very long post for such a simple question!)

Cheers!

Matt

Reply to
larkim
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with internal stopcocks rising up from the solid floor.

water taps, and the other main supplies a handful of other cold outlets.

have PRVs attached.

thermostatic mixing bar shower to regulate the temperature properly, as it seemed that the pressure of the cold supply was overwhelming the hot.

mixer shower, such that it is always at a temperature just below ideal - no matter what I do to the temperature adjustment (including removing the head and adjusting it) it comes out at the same temperature. To make my showers more enjoyable I have taken to leaving a cold tap running (supplied from the same main as the cold feeding the shower), which works (just) and raises the temperature to a reasonable one.

PRV to resolve this.

formatting link
which has a black cap and a screw in the top.

top? However, doing this appears to have no impact on the gauge reading.

the shower I had was nearly freezing because I clearly had had some "impact"!) that waiting for the pressure gauge to move whilst there was no cold water flow taking place was probably misguided.

in flow (and if so, how much flow? Full taps open, or would less than this suffice?) And am I barking up the wrong tree trying to adjust the pressure on the cold side to have an impact on the shower temp?

I have a feeling I saw one once where (presumably to deter twiddling) it wasn't as simple as turing the knob. I *think* you had to tighten a screw first. Sort of variation of "child-proof pill bottle".

Reply to
newshound

oth with internal stopcocks rising up from the solid floor.

ld water taps, and the other main supplies a handful of other cold outlets.

ins have PRVs attached.

thermostatic mixing bar shower to regulate the temperature properly, as it seemed that the pressure of the cold supply was overwhelming the hot.

e mixer shower, such that it is always at a temperature just below ideal - no matter what I do to the temperature adjustment (including removing the h ead and adjusting it) it comes out at the same temperature.  To make my s howers more enjoyable I have taken to leaving a cold tap running (supplied from the same main as the cold feeding the shower), which works (just) and raises the temperature to a reasonable one.

the PRV to resolve this.

he top?  However, doing this appears to have no impact on the  gauge re ading.

(when the shower I had was nearly freezing because I clearly had had some " impact"!) that waiting for the pressure gauge to move whilst there was no c old water flow taking place was probably misguided.

er is in flow (and if so, how much flow?  Full taps open, or would less t han this suffice?)  And am I barking up the wrong tree trying to adjust t he pressure on the cold side to have an impact on the shower temp?

Yes they are adjustable. However the adjustment is counter-intuitive, you screw the screw in (clockwise) to increase pressure.

Reply to
harry

both with internal stopcocks rising up from the solid floor.

cold water taps, and the other main supplies a handful of other cold outlet s.

mains have PRVs attached.

he thermostatic mixing bar shower to regulate the temperature properly, as it seemed that the pressure of the cold supply was overwhelming the hot.

the mixer shower, such that it is always at a temperature just below ideal

- no matter what I do to the temperature adjustment (including removing the head and adjusting it) it comes out at the same temperature. To make my s howers more enjoyable I have taken to leaving a cold tap running (supplied from the same main as the cold feeding the shower), which works (just) and raises the temperature to a reasonable one.

to the PRV to resolve this.

the top? However, doing this appears to have no impact on the gauge read ing.

g (when the shower I had was nearly freezing because I clearly had had some "impact"!) that waiting for the pressure gauge to move whilst there was no cold water flow taking place was probably misguided.

ater is in flow (and if so, how much flow? Full taps open, or would less t han this suffice?) And am I barking up the wrong tree trying to adjust the pressure on the cold side to have an impact on the shower temp?

I think I've got one like that on the combi - you need to undo a large bras s screw first to allow the adjusting barrel to rotate.

Reply to
larkim

Just read your post again. For the pressure guage to move, you have to adjust the reducing valve with water going through it, ie run a tap somewhere on the pipe it is feeding. Just a trickle is enough.

Reply to
harry

both with internal stopcocks rising up from the solid floor.

cold water taps, and the other main supplies a handful of other cold outlet s.

mains have PRVs attached.

he thermostatic mixing bar shower to regulate the temperature properly, as it seemed that the pressure of the cold supply was overwhelming the hot.

the mixer shower, such that it is always at a temperature just below ideal

- no matter what I do to the temperature adjustment (including removing the head and adjusting it) it comes out at the same temperature.  To make my showers more enjoyable I have taken to leaving a cold tap running (supplie d from the same main as the cold feeding the shower), which works (just) an d raises the temperature to a reasonable one.

to the PRV to resolve this.

the top?  However, doing this appears to have no impact on the  gauge reading.

g (when the shower I had was nearly freezing because I clearly had had some "impact"!) that waiting for the pressure gauge to move whilst there was no cold water flow taking place was probably misguided.

ater is in flow (and if so, how much flow?  Full taps open, or would less than this suffice?)  And am I barking up the wrong tree trying to adjust the pressure on the cold side to have an impact on the shower temp?

Yes, I think that was what I interpreted from their arrows on the dial. So long as it is just that screw, and nothing to do with the black surroundin g too.

What about the point about reading the gauge whilst the flow is in action? Does that make sense?

Matt

Reply to
larkim

Brill, thanks!

Reply to
larkim

"Instructions for Use" for Reliance Easi-set 320 Series PRVs.

Operation The Easi-set 320 series pressure reducing valve is equipped with a lift and twist adjustment mechanism. To adjust the pressure pull the knob into the UP position. Turn the knob as indicated on the top (-) to the minimum setting until the control knob hits the stop. Next open a tap downstream to bleed off the excess system pressure, then close the tap. Now turn the the control knob as indicated to increase the pressure (+) until the desired pressure is established. Finally push the valve control knob back down into the locked position.

The maintenance section says that an increase in pressure may be due to a defective check valve down stream or dirt in the valve seat.

Reply to
Dave Liquorice

Sounds silly, but have you checked the incoming hot water inlet temperature? What sort of flow do you get from your hot taps?

It's not unknown for mixers to misbehave, and in your position I would replace your existing mixer with a thermostatic one. The warm up time would be quicker and the temperature more stable, even when someone flushes a toilet in your house!

Reply to
Fredxx

OK thanks - I presume you are posting that instruction set as general guidance on how to set the pressure, as I don't have that particular model of PRV. Will attempt to read and deploy tonight!

Matt

Reply to
larkim

Sorry, thought I mentioned it - it is a thermostatic bar shower, not a mixer.

Matt

Reply to
larkim

Correct, that is why I fully quoted the make/model. With a gauge attached to the valve it ought to work with just a gentle bit of flow and adjusting the knob. The Reliance valve doesn't have a gauge or pressure monitoring point.

Reply to
Dave Liquorice

If you are in a hard water area, they can scale up and stop working. Remove and descale in a washing up bowl (or something similar) with a descaler (such as Furnox DS-3). There may also be a mesh filter in the inlet pipes which has become clogged - check when you remove it.

(Thermostatic bars are not ideal for combis because they have a slow response to changes in input temperature and are affected by input pressure changes. You ideally want a fast response mixer designed for combis and multipoint water heaters, which are designed to handle sudden changes in input temperature and pressure. However, they are significantly more expensive.)

Reply to
Andrew Gabriel

There are two types of domestic water pressure, static and {not static}.

For an extreme example, suppose you have a mains pressure of 10 bar and a blanking plate in your supply with just a pinhole through it.

With all the taps turned off your static pressure should (eventually) be

10 bar.

However as soon as you turn a tap on the pressure would drop to (I think)

1 bar atmospheric pressure.

So to see what pressure you have in real life I think you have to have a tap running.

[See how you forget even the simplest physics over the years - no doubt an expert will be along shortly :-) ]

One way to balance up your shower would be to fit a service valve on the cold supply and gradually close it until the mixer can cope.

Cheers

Dave R

Reply to
David.WE.Roberts

It sounds more like you have a thermostatic mixer valve for your shower which is misbehaving rather than a problem with your PRVs.

Most thermostatic mixer valves have a "max temperature" preset screw somewhere and it's possible that scale build-up has reduced this set point. That would cause the same problem as you're experiencing.

Tim

Reply to
Tim+

Thanks - yes, I've puzzled over the concept of pressure in the system for a short while now, and I do understand what you are saying.

Unfortunately the plumbers that put in the shower didn't think to leave spa ce for a service valve (something I'm putting right in the spec for a diffe rent bathroom which needs sorting) - irritating as the back of the shower i s a studwall which could accommodate a simple access hatch without too much visual impact.

With a little bit of trial and error we sorted it out last night, and now I am thoroughly well showered and warmed up!!

Matt

Reply to
larkim

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