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Discuss Cap internal blow off (prv) and fit on pipe work instead? in the Central Heating Forum area at

  1. Jones82

    Jones82 Member


    I'm Gsr by the way and should get around to sending in my card details.

    I'm working on a system boiler and central heating system and the prv/vessel has recently failed, I'm finding it difficult to source the prv short notice, I'm thinking of capping the Prv inside the boiler or the existing discharge pipe work then fitting a new one on the return pipe work close to the boiler, I'm already fitting a replacement external expansion vessel and filling loop so perfect time to do it.

    The existing internal vessel has split and is undersized.

  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Sorry to say no no no and you can't cap the boiler one as it's protecting the boiler and the system
  3. Jones82

    Jones82 Member

    If it was a combi then I wouldn’t even think about it, as someone could isolate the heating and run hot water but it’s a system boiler, if you isolate the heating then the boiler wouldn’t work at all. The by pass and vessel are external, why not the prv? Its common practice on heat only boilers?
    • Optimistic Optimistic x 1
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Does the boiler have valves if yes then it's still a no

    What boiler is it ?
  5. Jones82

    Jones82 Member

    Remeha advanta plus and it has the usual isolators on the flow return and Gas as they enter the boiler. But if you shut these on a system boiler or even a modern heat only boiler then the flow switch won’t allow the boiler to fire ?
  6. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Still doesn't matter what happens if the flow switch sticks etc if it has valves you can prv needs to be in the same place

    And no you can't put one / a new one after the old prv
  7. Jones82

    Jones82 Member

    Yes I guess your right it would also be against the manufacturers instructions.

  8. tolly

    tolly Plumber GSR

    I thought some manus allowed remote prv as long as you tee the boiler PRV into the return after the iso's.

    No idea if remeha allow this though
  9. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    This requires the boiler prv to be new tho

    Or a manufacturer link kit/ remote kit
  10. firemant

    firemant Plumber GSR

    Can't do link Adobe mobile. But I fitted a Baci system on my own home and was awkward for PRV. Followed their instructions but did not buy their kit. Plumb BLR PRV into return (?) . Fit remote PRV but had to be the highest point IIRC. Can't remember but the instructions are available online
  11. Gasmk1

    Gasmk1 GSR

    it is against gas safety regs as you are altering the design of the boiler
  12. Last Plumber

    Last Plumber Plumber GSR Top Contributor!!

    If it has isolation valves beneath the Boiler I would say no. You do not want a situation where the boiler can be isolated without any form of relief.
    If you permanently removed the isolation valves then it would be safe.
  13. Chalked

    Chalked Plumber GSR

    Another problem with h doing it that way, is that the valve would be open and the valves are not designed to hold pressure on the outlet side of the valve.
  14. tolly

    tolly Plumber GSR

    Ive never come accross a heat only with isos underneath or on top?
  15. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    System boiler
  16. tolly

    tolly Plumber GSR

    System boiler yes. But he said "modern heat only boiler"
  17. tolly

    tolly Plumber GSR

    I dont call system boilers heat onlys.
  18. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Heat onlys don't have prvs
  19. tolly

    tolly Plumber GSR

    I know, read the message i quoted bud. He wrote about closing iso's on heat onlys...thats why i said ive never come accross a heat only with iso's. Incase it goes kaboom with no prv.
  20. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    40cdi has ISO valves and no prv there out there
    • Like Like x 1
  21. tolly

    tolly Plumber GSR

    You sure? Was at a 40cdi conventional last week.
  22. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    TBH not 100% sure as I installed it 2 years ago
    • Like Like x 1
  23. Jones82

    Jones82 Member

    Your right my mistake, modern heat only's I've fitted don't have iso's and now I know why!
    • Like Like x 1
  24. Ric2013

    Ric2013 Plumber Top Contributor!!

    I've worked on a heat-only installation that had restrictive quarter turn isolators on a heat-only boiler. I removed the isolators for obvious reasons.
  25. richard978

    richard978 Member

    Don't be silly, if you have your CCN1 and CENWAT then you should know why.

    The Avanta is actually made by BAXI and the parts are easy to come by. The issue is replacing them as with most expansion vessels changing them is labour intensive and rear flues often obstruct the vessel.

    I can tell you the HYDRO blocks on those are evil to change, I did one last year and it had me sweating.

    Maybe its time for a new boiler, its probably 10 years old/
    Last edited: Dec 8, 2017 at 7:46 PM
  26. dan_the_plumber

    dan_the_plumber GSR

    I would say speak to manafacturer. See if they do a specific ‘remote PRV set’. If not then don’t do it :))
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