Pressure relief valve off CH pipe

[JohnHarrison]

A neighbour/friend is to renovate his flat. We live in an old block of flats. The flats have chimney breasts in each room, inc kitchen, which almost everyone have blocked up or made cupboard space out of them. The chimneys are internal, not being on external walls.

Now, he is considering opening his kitchen breast, making a large cupboard out of it and fitting a combi boiler inside running the exhaust pipe up the flue making the it room sealed. The roof is flat so easy access the for the flue terminal. The exhaust flue pipe will be about 20 foot in length. The breast is about 20 feet from an outside wall. There are two problems which one is easy to overcome.

1) The condensate drain can have a condensate pump and pumped under the floorboards (2"gap) in a plastic pipe to a HepVo trap near a drain near the outside wall. Or fit a non-condensing Vokera SE, which will be exempt. This is not a real issue. If a condensing boiler is chosen he is considering an Intergas, which is highly thought of, with the outside sensor wire run up the flue to be screwed to the side of the chimney stack on the roof.

2) The pressure relief pipe. The question: Can the pipe on the combi be teeded into a CH return pipe, then another pressure relief valve teed into the CH pipe that runs near the outside wall, 20 foot away and run through the wall fitting one of the neat terminating buttons? I see no reason that it cannot be done. The boiler valve if it opens discharges into the CH pipe, so any pressure in the boiler is got away immediately, which 20 foot away has another pressure relief valve which opens up to the atmosphere. Both valves would be 3 bar opening pressure.

This forum's software is so slooooow.

Thanks for any "sensible" replies.

 

[45yearsagasman]

That cannot be done. What if the plate failed? What would happen to the system water? It could possibly contaminate potable water. That is my way of looking at it, might be wrong, but I'm happy to be corrected.

 

[JohnHarrison]

That cannot be done. What if the plate failed? What would happen to the system water? It could possibly contaminate potable water. That is my way of looking at it, might be wrong, but I'm happy to be corrected.

Gasman I think you got it wrong. The second pressure valve is teed into the CH piping, with no CH valves between it and the combi, not the potable water pipe. If a plate heat exchanger failed and contaminated system water enters the potable water pipe, then that is the situation on all combis with plate heat exchangers. BTW, the two combis that are in mind do not have plate heat exchangers.

 

[Biggles..]

If the prv can't be terminated you can tee boiler PRV into heating return and then fit a remote valve, this should be on an un obstructed primary circuit pipe.
Usually they are a slightly lower pressure than the 3bar boiler.
Some manufacturers offer this as a kit, for example Vaillant/baxi

 

[45yearsagasman]

then that is the situation on all combis with plate heat exchangers.

I agree with that, but manufacturers design has been approved by all water authorities. All inst instructions that I've ever seen don't include your method of connection. You have to ask why that is. Plates or dual pass heat exchangers that fail could result in cross contamination.

 

[JohnHarrison]

then that is the situation on all combis with plate heat exchangers.

I agree with that, but manufacturers design has been approved by all water authorities. All inst instructions that I've ever seen don't include your method of connection. You have to ask why that is. Plates or dual pass heat exchangers that fail could result in cross contamination.

Gasman, cross-contamination is not an issue here, as that is a general topic, not specific to this. The issue is feeding the pressure relief valve immediately back into a CH pipe rather than to atmosphere, and take off another pressure valve at the far end of the system 20 foot away. This way any pressure at the boiler is pushed into the flow or return pipe and another valve opens 20 foot away releasing pressurised water to atmosphere.

 

[JohnHarrison]

If the prv can't be terminated you can tee boiler PRV into heating return and then fit a remote valve, this should be on an un obstructed primary circuit pipe.
Usually they are a slightly lower pressure than the 3bar boiler.
Some manufacturers offer this as a kit, for example Vaillant/baxi

LeeC, thanks that is what I wanted. So it is a case of getting hold of a PRV less than 3 bar opening pressure.

I assume these Vaillant/baxi kits can be fitted to any system then?

 

[45yearsagasman]

As I said, I'll stand corrected. I'll get me coat, and see myself out.

 

[Biggles..]

If the prv can't be terminated you can tee boiler PRV into heating return and then fit a remote valve, this should be on an un obstructed primary circuit pipe.
Usually they are a slightly lower pressure than the 3bar boiler.
Some manufacturers offer this as a kit, for example Vaillant/baxi

LeeC, thanks that is what I wanted. So it is a case of getting hold of a PRV less than 3 bar opening pressure.

I assume these Vaillant/baxi kits can be fitted to any system then?

Not all manufacturers will approve the method, so you will have to check with whom ever you choose.

 

[JohnHarrison]

Bax sell a valve called the ..
Baxi Remote Secondary Safety Relief Valve 5121379

I assume this is rated at 2.5 bar. For just a valve it cost £22 or so plus del. A quick Google and the cheapest 2.5 bar was £18 inc del with a gauge.
http://www.advancedwater.co.uk/prod-263-468-0706.html

 

[Onetap]

2) The pressure relief pipe. The question: Can the pipe on the combi be teeded into a CH return pipe, then another pressure relief valve teed into the CH pipe that runs near the outside wall, 20 foot away and run through the wall fitting one of the neat terminating buttons? I see no reason that it cannot be done. The boiler valve if it opens discharges into the CH pipe, so any pressure in the boiler is got away immediately, which 20 foot away has another pressure relief valve which opens up to the atmosphere. Both valves would be 3 bar opening pressure.

No.

You cannot be serious.

How would you know that it (the first PRV) had discharged? How would you test it? How would you know if it was letting-by? The safety device must be on the boiler.

It is a safety device and is not to be buggered about with.

 

[JohnHarrison]

Onetap, Valliant and Baxi do it I now know. The secondary PRV is set to 2.5 bar. Read the thread.

 

[Biggles..]

Onetap in this instance you aren't upto date with what's available.

Even the reasoning by your argument doesn't make sense when the remote kits operate before the boiler valve.

 

[Onetap]

Onetap, Valliant and Baxi do it I now know. The secondary PRV is set to 2.5 bar. Read the thread.

No they do not. Link please.

The device you have posted a link to is a Secondary PRV for installation on a heating system. It operates in conjunction with the boiler PRV, it does not replace it. There is still a statutory need for a PRV on the boiler that discharges to atmosphere.

This is a separate issue to connecting the PRV discharge into a CH pipe that may be blocked with sludge or become frozen. It is a stupid idea. Please delete all mention of it and never suggest such a thing again.

Onetap in this instance you aren't upto date with what's available.

Even the reasoning by your argument doesn't make sense when the remote kits operate before the boiler valve.

What is available? Please enlighten me.

The boiler comes with a PRV fitted directly to it, not several metres away. It is there for a good reason. The PRV discharge pipe is to be connected in accordance with the manufacturer's installation instructions. This does not allow for innovative connections to the CH systems by morons.

 

[JohnHarrison]

They call the remote pressure valve the "secondary". As is activates first it must be the primary.