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Discuss Heat only to system boiler in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. Cheque

    Cheque New Member

    Thanks to everyone for the useful info on the forum. I used to work in plumbing many years ago but things have definitely moved on a lot since then and I would appreciate some specific advice.

    I currently have a heat only boiler in garage with header tank in roof space. I upgraded a number of years ago to an unvented hot water cylinder but I am now considering getting a system boiler fitted and pressurizing the central heating/hot water loop. Current boiler is 15 years old and the system has been drained down quite often recently for fitting radiators but takes an age to fill and a number of days to flush out the airlocks. I guess I'm also expecting it to be close to the end of its life.

    Most of the central heating is unfortunately in 8mm microbore. My main concern with doing this is if the extra pressure exposes any leaks behind tiled walls/floors for instance. I presume it would more likely be compression fittings that could be problematic than any of the soldered fittings on the main 22mm pipes/manifolds? I realise that there are leak products you can add but how sensible is this with a microbore system as I presume they leave some kind of residue - is there a possibility that this reduces the flow? Also know people that need to top up regularly which sounds like a nightmare and I presume is down to undetected slow seepage somewhere.

    I take it this is quite a common upgrade and wonder if anyone can comment on how much of a problem it is in reality?
  2. gmartine

    gmartine GSR

    What is your existing heat only boiler, you may actually be able to pressurise it.
  3. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Leak sealant absolutely last resort can gum up boilers
    • Like Like x 2
  4. townfanjon

    townfanjon Trusted Plumber GSR Top Contributor!!

    As long as the pipes are not buried in the walls and floor , pressurise it , if theres a leak , find it and fix it.
    • Like Like x 1
  5. Rob Foster

    Rob Foster Top Contributor!!

    carry on with the existing system, no leak sealer, stick a mag and debris filter on, if you really want to see what happens
    then give it squirt of mains pressure ...connect drain off to outside tap open gently see what happens, isolate F and E close valve and use a champers cork for the vent , if all holds happy days ...u can use this method to re fill after a drain down as well minus champers cork and closed valve. pressure systems do leak even small amounts
    and the leak is often undectectable...there is a solution
    Rob Foster aka centralheatking
  6. scott_d

    scott_d Plumber GSR Top Contributor!!

    it is possible to seal open vent systems if the boiler manufacturer allows
    • Like Like x 2
  7. Rob Foster

    Rob Foster Top Contributor!!

    yes but do not forget an exp vessel and if you are not qualified dont do,it centralheatking
    not aimed at you Scott you are GSR
    • Like Like x 2
  8. Chuck

    Chuck Well-Known Member

    I think many people worry too much about pressurising a system 'causing' a leak. If pipework does leak when pressurised it's a downer but it was probably only a matter of time. Even a relatively slow leak from an open system can do quite a lot of expensive harm if it causes rot and other damage before it is noticed.

    In any case, you can choose your moment to pressurise and do it at the start of the summer when it's not too cold and you have time to fix problems or renew the installation. Far preferable to having to deal with such problems in the middle of winter.
    • Like Like x 3
  9. Cheque

    Cheque New Member

    Thanks confirmed my suspicion that leak sealer not a good idea. Just trying to understand pros/cons before getting somebody in. Find and fix will be OK assuming its not tiled in i.e. in my new bathroom..

    I thought replacement may be more economical in the long run as I understood modern condensing boilers are doing well to reach 15yrs. Also reluctant to spend any money on the glowworm boiler I have even if its just an exp vessel/pressure gauge etc and labour.

    I presume for replacement you would all recommend going pressurised and not sticking with header tank? I understood it to be better for corrosion in the system. Any pros to a heat only with external pump/exp vessel over a system boiler?
    • Like Like x 1
  10. Rob Foster

    Rob Foster Top Contributor!!

    What Gloworm ? have a look at ignite heat spares they have kept my gloworm alive for years
    Rob Foster aka centralheatking
  11. Cheque

    Cheque New Member

    Its a british gas one 330 (24kw). May well be throwing away some thing that will last a lot longer just based on what I've read seemed like its probably done well and to be fair its had a hard life!
  12. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    TBH as it’s 8mm I would recommend a re pipe in 15 drops and 22mm runs
    • Agree Agree x 1
  13. Harvest Fields

    Harvest Fields S. Mod Trusted Plumber GSR Top Contributor!!

    Repipe for me too. You want it to be as effiecent as possible.
    • Agree Agree x 1
  14. John.g

    John.g Active Member

    A semi-sealed system, retain the F&E tank, blank the vent, fit a AAV at the highest point, install a swing check valve in a horizontal portion of the cold feed,
    Semi sealed system, blank the vent & fit a AAV at its highest point, install a swing check NRV in a horizontal section of the cold feed, install a expansion vessel with pre pressure set to 0.5 bar. Some say its the lazy man's way of doing things but its more forgiving than a fully sealed system especially if a large expansion vessel is fitted, no manual top ups needed or no (horrible) auto fill valve, it is/was quite popular in some areas where a gas fired boiler (with integral exp vessel) replaced a gravity fed oil boiler.
    • Informative Informative x 1
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