putting a second prv in line

[Billy Bob Bob]

it was suggested i do this rather than remove the boiler from the wall,,being the sort that does things correctly i have issues with doing this,surely if you put a prv in line with the old one effectively having 2 3 bar prv,s you are asking for trouble in the event of a problem,anyone else agree?

 

[Dotty]

Wouldn't be happy doing that either Mark.

I'd rather reroute the existing prv discharge into the return pipework and fit a new prv also on the return.

 

[chris watkins]

Apart from the increase risk of leaking I don't see the problem.

converting an old OV system to a sealed one the PRV goes ware you put it on the system or with the Robokit.

 

[lame plumber]

what if the first/old prv is jammed shut being as its knackered anyhow I would bin it for a new one, not for the next 2 weeks though I am presuming you mean you put the replacement on the drain off line behind the original one.

 

[Billy Bob Bob]

Apart from the increase risk of leaking I don't see the problem.

converting an old OV system to a sealed one the PRV goes ware you put it on the system or with the Robokit.

yes but we are talking a combi here,for one thing you are technically altering a safety device,thats where i see a problem

 

[Billy Bob Bob]

what if the first/old prv is jammed shut being as its knackered anyhow I would bin it for a new one, not for the next 2 weeks though

thats what i am thinking,how many old ones have we seen that dont go off at 3 bar because they are shot

 

[lame plumber]

however I have sometimes had to run a prv from some other part of the system and run the original one straight back into the ruturn as per croppies post, all done with manufacturers blessing. Just label the original prv to show where the other one is.

 

[chris watkins]

yes but we are talking a combi here,for one thing you are technically altering a safety device,thats where i see a problem

OK but technically isn't the pressure uniform across the whole system ?

 

[Billy Bob Bob]

OK but technically isn't the pressure uniform across the whole system ?

yes,i dont see a issue with putting one elsewhere in the system,just inline with the old

 

[mfgs]

I agree with you, its not something I would do. However in theory is there actually anything wrong with it? The fact you normally replace a prv is because it is passing, obviously if you are there because its not opening at all then there is an issue. Then the first prv will open at 3 bar and the second shortly after as there wont be much pipework in between. The argument that one might fail to open is redundant as a brand new one is probably just as likely to have that same issue.

 

[chris watkins]

yes,i dont see a issue with putting one elsewhere in the system,just inline with the old

Oh sorry do you mean one after the other i.e. install another on the discharge pipe from existing ?
If so then No way hosay. At a push I would cap the discharge & install elsewhere.

Apologies for my misunderstanding.

 

[Chalked]

It won't work. If the old one permanently opens and the second one is shut ( as it should be) it may leak through the top of the existing valve, the only part rated to the pressure is the seat and washer.

 

[Billy Bob Bob]

Oh sorry do you mean one after the other i.e. install another on the discharge pipe from existing ?
If so then No way hosay. At a push I would cap the discharge & install elsewhere.

Apologies for the my misunderstanding.

no probs

 

[Leo21]

Surely it's not right, a 3 bar valve plus whatever restriction the first offers would increase the pressure it would blow off.
Putting it remotely is sound thinking to my mind, just get ready for stupid phone calls from other engineers spotting it , and not knowing what you've done.

 

[Ollieg]

You can't put remotely because you can isolate the heat source from the safety valve. With the flow and return isolation valves.

 

[Ollieg]

At least that's my reckoning

 

[mfgs]

At least that's my reckoning

That's why you should tee it into the return, although that's then essentially two inline again.

 

[Billy Bob Bob]

At least that's my reckoning

i can see your reasoning,isos off,no prv,pretty much the same as a ov boiler not having isos so it can vent over

 

[kris]

You can't put remotely because you can isolate the heat source from the safety valve. With the flow and return isolation valves.

Surely if you isolate the heat source it wont be being used as no where for water to travel , or am i missing something,,

In theory 2 safety features inline should be fine , id never do it and its really up to your own judgement and experience , 2 in parrarel is alot better than 2 in series, just remember why you need a new one , is it becuase the old ones faulty if so inline is out of the question,