Combi boiler mains pressure

[Jethro Tull]

I have a Vallaint eco-Tec plus 832. When the boiler was fitted five years ago, the engineer put a pressure valve on the mains and set it to 3 bar. That would be OK but the pipe for the boiler is taken off from the pipe which goes upstairs and also to the front hose tap. So what I have is low pressure on one section of the system. Downstairs fine but upstairs low in comparison and the hose pressure is diabolical. My question is, can I turn up the mains pressure to the upstairs and just control the boiler pressure at the boiler itself using the loop. Or is the loop just for central heating and seperate friom the hot water system? He told me that the mains pressure was too high but why would that make any difference? Any suggestions will be gratefully received.

I think I have worked this out but correct me if I am wrong.
I am thinking of installing another PRV on the 15mm pipe which goes direct to the boiler from the mains T juction and then opening up the one the engineer put in to max pressure, equaling out the other cold water pressures to upstairs.

 

[DP]

There is no need for a pressure reducing valve unless mains pressure is too high.
Your boiler should be able to supply around 11 litres of water from the hot tap. Are you getting that?
With PRV fitted, there should also be a mini expansion vessel fitted after the PRV- look at the boiler manual for this

 

[Jethro Tull]

Thanks for your response. As I said, the engineer said it was too high and that was why he fitted the PRV and turned it down to 3 bar which is less than the ground floor cold system. There is a long silver tube with 'centre' written on it so I suppose that's the expansion vessel you mean. So in effect I am adding another PRV and opening up the original one (negating it really) to give the whole house the same pressure and keep the boiler at the 3 bar. I am quite OK with the pressures and heating otherwise, just the cold water for the garden and upstairs really. What do you think?

 

[Madrab]

The loop is just for the system pressure and not for the HW pressure. You say the PRV was put on the mains? If that's the case then all the cold outlets should be the same. Unless you mean the PRV was put onto the cold mains feed to the boiler - that then runs outside and upstairs? If the latter then

A PRV set to 3 bar should be able to deliver plenty of pressure to all the outlets that are connected to it, unless the dynamic pressure is crap or unless the PRV is now faulty.

TBH if you mains is so high it needs a PRV set to 3 bar to protect the boiler (not really needed these days) then all the cold outlets should be run from a mains PRV at the upstream mains stop tap to the house.

 

[Jethro Tull]

The PRV was fitted BEFORE the pipe to the boiler and first floor but AFTER the down stairs plumbing. So the downstairs has good pressure only. 3 bars is what the engineer set the pressure to when he fitted it. Cold water to the downstairs is good and the back garden hose is good too. The upstairs and front garden hose fitted AFTER the PRV is crap and always has been that way since the boiler was fitted. I don't know what the downstairs pressure is but it seems to be around 4 bars that's why he reduced it to meet the needs of the boiler. Btw the manual for my boiler states 3 bar max. So half the house has low pressure and one half good pressure.

 

[grahamderek]

"3 bar max" is the heating side pressure. DHW max is 10 bar. Maybe the installer fitted a prv to protect substandard pipework, but not to protect the boiler.

 

[Elsa TLC]

Maybe you PRV is buggered

 

[Jethro Tull]

But he actually reduced the pressure when he fitted the boiler with the PRV. The downstairs remains as it was, so there is a disparity between the two floors. So what I thought was, I would try fitting a new PRV into the specific pipe going to the boiler so it won't interfere with anything else. But even if the first PRV is naffed it won't be needed anyway if I open it up fully. Thank you again for your time.

 

[DP]

As Graham stated, boiler is fine with 10 bar pressure ( not looked at the manual myself.)

Post a picture of the mini expansion vessel.

Sometimes plumbers fit a pressure reducing valve and set it to say 1.5bar to aid filling the radiator side of the installation. Boiler will eject the system water ( radiator side) when 3 bar pressure is reached.

A PRV will allow water to pass through but will block water flow in reverse direction. When boiler heats water for hot tap, after you are finished with hot water, residual heat within the boiler will continue to heat the water which is now trapped between the hot water taps and PRV. In some cases this expansion will damage hot water components within the boiler hence need for mini EV

Pressure reducing valve needs high pressure on the inlet to give you preset pressure on the outlet. Say your PRV is set to 3.5 bar. In theory all the taps on the outlet will in theory deliver this pressure unless the mains cannot support the flow

If you are concerned. Remove the PRV and fit it to the boiler leaving rest of the cold supply at mains pressure.

 

[Jethro Tull]

I don't where all the reply buttons have gone. But thanks for all your replies. The engineer did say at the time that the max for the Vaillant was 3 bars because I wrote it down at the time.

 

[Jethro Tull]

The first image should be vertical. The pipe above the stop cock goes under the floor and supplies to downstairs cold water system.

 

[Jethro Tull]

Thanks DP I can't reply direct as there is no reply button showing but this is what I am thinking.

 

[DP]

Thanks DP I can't reply direct as there is no reply button showing but this is what I am thinking.

Highlight the text and use Quote button.

The silver thing is a scale reducer for the boiler.
Was the cold after the PRV always 15mm?

In say the bathroom, run a cold tap. While watching the flow, run a hot tap. Does the cold flow reduce? What does the pressure gauge indicate while the cold and or hot tap is running. Something does not make sense.

 

[Jethro Tull]

Yes it is as it was always 15mm. I tried the upstairs tap when the extension was finished but as I am still working on it I have turned all water off for the time being but I know it is the same pressure as the front tap which as I say is poor. So the circuit is in two sections, the full original pressure downstairs and the rear garden tap and the pressure after the PRV was fitted upstair and the front tap as you can see with the location of the reducer valve. Let me just add that a low pressure in the upstairs bathroom isn't so much of an issue, it's the front tap which is a real pain. It takes ages to water the garden. The downstairs shower is fine too so the boiler is OK. I just need more pressure after the PRV. This is why I am thinking of moving it to the main boiler feed pipe.

 

[Jethro Tull]

Listening to the comments here I think what I might now do is see if I can T off before the PRV to the front tap and leave the rest well alone. It will be a squeeze to get it in but I think I can just about fit a 22 x 22 x 15mm compression. I think it's too risky not being a qualified heating engineer to chance anything Thanks again for all the assistance as it has really helped me come to a decision.