Is my pressure reducing valve in the correct location?

[sonnyred]

I have a Vaillant system boiler and Vaillant hot water cylinder, when someone runs a tap anywhere in the house the shower changes temperature and the pressure drops. I am wondering if this is due to the location of the pressure reducing valve.
The mains water goes straight to the PRV, from there it splits to the boiler and also back to the rest of the house to feed everything else including toilets, sinks etc. Should everything in the house be at this reduced pressure or should only the boiler be at this lower pressure?
Thanks.

 

[Madrab]

Depends, what is the reduced rate and what is the dynamic mains pressure.

 

[Johntheo5]

A outside tap is generally straight off the mains I think and the kitchen tap may or may not be likewise.
Assuming a unvented cylinder then a combination valve is normally used as the hot&cold are allways at the same pressure (but can rise and fall a bit depending on the volumes of water required).

 

[Madrab]

The long and the short of it is, hot and cold water supplies should be pressure balanced therefore if the hot water pressure has been reduced then you want to reduce all the cold outlets that may used the cold through the same outlet. Avoids any issue with mixer/mono bloc taps.

If you have a system boiler the cold water mains won't go to the boiler. If it's an unvented then yes, the hot and cold should be balanced.

 

[sonnyred]

Thanks for the replies, sounds like everything is correct.
Yes it's an unvented cylinder, so why would someone opening a tap anywhere in the house cause the pressure to drop and change the temperature in other outlets?
I remember when the system was fitted, there was plenty of pressure and flow in the cold main.

 

[Johntheo5]

How many PRVs have you got, assuming you have one like above, in the combination valve?.

 

[JonathanM]

I remember when the system was fitted, there was plenty of pressure and flow in the cold main.

So, is this a new problem? Has the shower worked OK in the past? Has the cold pressure dropped? Is it just a problem with the shower, or does it affect other taps as well?

 

[Madrab]

Have you ever had the system/unvented serviced?

 

[sonnyred]

How many PRVs have you got, assuming you have one like above, in the combination valve?.

Just 1 and yes in the combination valve.

So, is this a new problem? Has the shower worked OK in the past? Has the cold pressure dropped? Is it just a problem with the shower, or does it affect other taps as well?

It's always been an issue, we've just lived with it. It affects all the outlets, if you're just running a cold water tap and flush the toilet the tap reduces pressure and the toilet takes longer to fill. The pressure seems absolutely fine if you run a single tap, just when you open another.

Have you ever had the system/unvented serviced?

Yes I've had the boiler serviced, not sure if the unvented cylinder was serviced.

 

[Johntheo5]

Can you post a few details from the PRV.

If you have a expansion vessel on the unvented cylinder see if it has a pressure gauge and note its reading with no demand fror water and with a demand, if no pressure gauge try and get hold of a "car" type P.gauge or pump with a P.gauge and attach it to the schrader valve on the end of the E.vessel. to get a few readings.

 

[Johntheo5]

Can someone comment on this?.

 

[Madrab]

get hold of a "car" type P.gauge or pump with a P.gauge and attach it to the schrader valve on the end of the E.vessel. to get a few readings.

Hi @Johntheo5 can I suggest that the OP doesn't play with his unvented? It needs a qualified engineer in to look at that. I appreciate it's just pre-charge readings but if the the OP doesn't get the connection right he could empty the EV, potentially causing more problems.

As far as the combination set is concerned then yes, the pipe out the bottom should be the cold mains feed to the cylinder. I would also think that the EV connection is correct as the NRV will be between that and the balanced cold feed as is the PRV.

The mains connection looks a bit strange mind you, usually everything on the valve is compression so nothing gets melted/burned if soldering.

 

[Madrab]

Yes I've had the boiler serviced, not sure if the unvented cylinder was serviced.

The unvented cylinder and associated items should be serviced yearly, as the boiler would. You can then point out the issues you are seeing and the attending engineer could check all of that.

 

[Johntheo5]

As far as the combination set is concerned then yes, the pipe out the bottom should be the cold mains feed to the cylinder. I would also think that the EV connection is correct as the NRV will be between that and the balanced cold feed as is the PRV.

Shouldn't the EV be conected to where the cold cylinder feed is now even though both downstream of the NRV, wondering if designated EV connections have a very small port, smaller than the takeoff bore which would have a huge effect on the pressure drop in the cylinder when HW drawn off. (If connected incorrectly to the cold cylinder feed).
Of course the cylinder may have a air bubble with no EV requirement and that bottom pipe is supplying elsewhere.

I'm allways a bit surprised that a pressurized vessel like a unvented HW cylinder hasn't got a pressure gauge installed as a standard feature.

 

[Madrab]

Some use the blanked off EV port on the valve, if there is one, they usually are part of the Pressure Relief Valve section so they are both downstream of the NRV, not all combination valves have one IME. Some just tee directly off of the feed, others have even fed the EV from the HW outlet side. That 15mm pipe that's heading right is heading into the bottom of a White EV. Some combination valves also have a gauge tapping but you're right, no reason why they should have a gauge in there as standard, guess it's a cost thing.

The EV shouldn't be considered like an accumulator though, it's there to balance the expansion pressure in the cylinder not increase the overall outlet pressure. Of course there can always be an increased pressure release initially but I would expect that should usually settle down within a sec or 2 and then sit at the (reduced) mains pressure.

Certainly a test of the unfettered mains and then checked on the downstream side of the valve would confirm the PRV is functioning correctly but I'd be tempted to check the dynamic mains, that would be my starting point, especially if it's been a problem from the start.

It does need an engineer in to service and then survey though.