Problem with pressure reducing valve?

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Happy New Year,
I have a problem with the hot water.
Our hot water works via a hot water calinder with inputs from a boiler and a solar panel loop.
The cylinder is made of copper and the inflow has a pressure reducing valving with a 2.1 bar rating. It has a 18l expansion vessel connected nad that was serviced and the pressure in there is about 1 bar. We also have a pressure and temperature relief valve on the cylinder, but they hardly ever / never get triggered unless for testing.
The cylinder heats up nicely and when we switch the hot water on in the shower or kitchen tap, we get plenty of water pressure. after a few minutes this nice water pressure evolves into a little dribble and when you wait the pressure will recover again but not to the original pressure.
There is no inflow obstruction / restiction. It is all 15mm pipe. The cylinder with all valves was installed together with the solar panel about 20 years ago.

Pressure Limiting Valve 3_1.jpg

I am wondering whether this odd water pressure is a sign of the pressure limiting valve being on its way out?
 
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Is it an unvented cylinder, being copper then I wouldn't expect so. Is the expansion vessel(EV) red or blue/white/grey?

If it is an unvented then the EV isn't at the correct pre-charge pressure. Also there may be an issue with the PRV if you are seeing a drop off in HW pressure.

If it's unvented then you need to get a qualified engineer to service it properly, once it's serviced properly then it should be back to normal. It may require parts though.
 
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Hi,
It is an unvented system with a copper rather than stainless steel cylinder.
The expansion vessel usedto be white and is now a blue one.
 
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OK, so pre-charge EV pressure is too low for a kick off.

The Pressure Reducing Valve (PRV) may need cleaned (filter) or adjusted/replaced. I am surprised that there is no pressure release valve associated with that PRV or is it further up the inlet line?

Ultimately you need to have a qualified and recommended unvented bod in to service the system properly. Once serviced you shouldn't have an issue. There is a flow restriction somewhere and it's taking time for the pressure to recover, especially given it's a 15mm feed.
 
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Are you describing a change to the system from when it was new, or has it always been like that.
@Madrab has described it adequately - a restriction in the supply
....we get plenty of water pressure. after a few minutes this nice water pressure evolves into a little dribble and when you wait the pressure will recover again but not to the original pressure.
There is no inflow obstruction / restiction. It is all 15mm pipe.
So you're quite sure there is no [additional] restriction?
Have you checked that the stopcock(s) is/are fully open. How does the hot flow compare to the cold water flow at the kitchen tap?
Does the cold kitchen tap water also drop off [in FLOW] after 'a few minutes'?
 
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The cylinder and pressure reducing valve together with the 15mm piping is all old since 2001 and fitted in the upstairs bathroom. We are on the 3. or 4. expansion vessel by now. The current one was fitted in July 2021. The pressure drop is a new thing.

The cold flow into the house is o.k. The bathroom upstairs gets the full pressure minus the drop / elevation.
The cylinder probably has a pressure limit, thus the 2.1bar limit in the cylinder pressure.
 
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Cylinder made by McDonald engineering by any chance? They would use low prv and group set. The ev could be acting as an accumulator. Needs to be looked at by someone that knows what there doing as mentioned. Pretty basic stuff to be honest.
 
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If the HW behaves the same regardless then it's probably an input issue. Invariably, the EV would be similar/the same as the Pressure Reducing Valve limit, as far as pressure set is concerned. If the system was serviced and the engineer left the EV @ 1 bar (if it was new then that's possibly the delivery pressure) then he doesn't know what he's doing and I suggest you get someone else in.

The fact it has a 15mm inlet also could also make it more susceptible pressure fluctuations especially if the EV is down.

Has anything else been changed recently?
 
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I had to get the old receipts out. The cylinder was from Newark Copper Cylinder Co. Ltd.
I also read through the instructions - to the installer - supplied from Newark for the first time properly. They say that the installer back then should have used a 22mm feed. Even though it has been fitted since 2001, we have not realy had a problem with the 15mm - maybe now. The pressure relief valve into the tundish is 3.5bar.
I will get someone when the trade are open next week.
 
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Just a follow up.
We have proper hot water pressure again.
A new pressure limiting valve is fitted this week. Adjustable this time, but I am sure that does not matter.
As I had the old one in the garage and it is servicable I opened it up. Scaled up and rusty inside.

P1224019.JPG


P1224020.JPG

I do not think this is reusable after servicing.
 
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I do not think this is reusable after servicing.
I think you're right there

Adjustable this time, but I am sure that does not matter
Yes, be careful, you don't want any more than the required pressure entering a copper unvented cylinder, In fact if it's adjustable there should be a pressure gauge on the inlet so the pressure can be monitored, you really don't want any more than 2.1 bar entering the cylinder.

It should really have been changed for Newark's own 2.1 bar PRV, they'll be designed specifically for copper cylinders.

https://shop.newarkcylinders.co.uk/spares-plumbing-supplies/22mm-pressure-reducing-valve-copper
 
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Hi,
There is a pressure gauge showing a pressue of about 2bar but when the hot water is on in the house it drops below that. What is important for us is that the flow is good again and not just a dribble.
 
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What is important for us

TBH ... The most important thing with an unvented is that the system is safe ..... unvented cylinders can be dangerous if the pressure is set too high or if the safety devices are compromised and then the pressure climbs too high.
 
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