PRV off a combi going vertical

[bster]

Seen alot of boiler installs with the PRV pipework going vertical.

I beleive it is safe going vertical as its releasing the pressure, but MI's allways tell you that it has to be a continuous fall - why?

 

[corgiman]

probably due to the fact that water will collect and MAY block up

I dont see it either

 

[bster]

I did see a combi today with vertical PRV but it had a drain off at the lowest point ( at the boiler)?

 

[Gasguru]

Sludge may collect and block the pipe.

 

[namsag]

Knew someone who took release pipe out with flue tube on most installs several years back..He called Baxi out for a few probs . They said you can`t do that, his reply was show me in instructions where it says that..... They then informed would change instalation instructions which they then did

 

[Paul Barker]

You were lucky in your area, round here they didn't even connect them up. There are no end of those worcesters with the prv on top and nothing attached to it. I guess sealed systems were relatively new then and nobody read MI's. I just find it absolutely amaising that after all these years they haven't had a massive flood.

There's me, impatient to rev up the system and I've had two floods so far, the second one occured the moment I finished telling the story about the first one. Now I always connect it up before opening the filling loop.

 

[Paul Barker]

Still at least my human errors don't kill anybody these days.

 

[Alfredo]

Of course you can do PRV "up and over", but you do have to fit a drain at the lowest point as it comes off the boiler No problems in my experience. You can also do condensate drain up and over with a pump. with some installs there is no choice.

Alfredo

 

[andsam]

What happens if the pipe goes up into the loft then to out side. The blow off has been leaking and its been extremely cold and the pipework has frozen, the pump fails and the pumpflow switch sticks.

Seen it happen.

 

[chrishutt]

Of course you can do PRV "up and over"

This is unacceptable. Any water held downstream of the PRV may cause serious problems.

 

[Paul Barker]

Don't forget from the unvented training that all prv's have a second safety which is that the cap on the face of the red part blows off if the prv fails to release the pressure, so a blockage upline of the prv would not be catastrophic there would of course be a flood.

Not that I agree with up and over, because I don't, but I don't see it as as big a problem as is being made out.

 

[chrishutt]

Don't forget from the unvented training that all prv's have a second safety which is that the cap on the face of the red part blows off if the prv fails to release the pressure,

First I've heard of that. Are you sure you don't mean the T&PRV? At what pressure is this supposed to happen?

 

[Alfredo]

So you've got an upstairs flat with concrete floors and no outside wall to mount the boiler. Whether you agree with up and over or say it is unacceptable suddenly becomes pretty academic. I've never seen it written that you can't do it, but we don't do it unless we have to, and sometimes there is no other way.

How many of you terminate a PRV with just a short pipe and (if you're lucky) a kick into the wall? Its so common, but the regs say down to ground level, and thats what we do. I've seen loads of condensate drains terminated without a soakaway and dripping onto ( no doubt slowly dissolving) brickwork below the dpc. Not on our patch

Our work is internally and externally QC'd and we haven't been pulled up yet for an up and over, but it is only used exceptionally. If the inspectors had a problem they would surely have raised it, as they surely pick up on other things from time to time.

Alfredo

 

[arfurrrr]

both vaillant and worcester bosch state

"the PRV pipework should be copper and have a continuous fall away from the boiler"

arf

 

[chrishutt]

Just consider a likely scenario. The PRV leaks slightly, perhaps a drip every minute or so. The water backs up in the vertical section of the discharge pipe. As the level in this pipe rises, so the back-pressure on the PRV outlet increases. This would tend to slow down or even stop the leakage. The rate at which water would be discharging from the open end of the discharge pipe might well be so slow that no one would notice or think it was of any concern.

The water left sitting in the vertical discharge pipe would be warm and in a warm environment. Evaporation would proceed quite rapidly, leaving deposits of scale and iron oxides behind. Within a matter of months these deposits might be sufficient to block the discharge pipe completely. With time the blockage would harden, thus rendering the PRV inoperative.

Unless someone systematically tested the PRV (and who dares to do that when servicing a boiler?) the blockage would remain undiscovered, at least until a critical situation arose. Then system pressure would rise until something else gave way to release the pressure, perhaps a radiator or pipe connection near a child.