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Discuss Steps to drain and re-pressurise this system? in the Central Heating Forum area at

  1. Ross87

    Ross87 New Member


    I’ve moved into a new house recently (mid 80s bungalow) and the central heating system is a bit foreign to me, I can’t even find a make or model on it anywhere... I’m in the process of a bathroom refit and need to relocate a radiator so I want to drain my central heating - could anyone help me out with the steps to drain and re-pressurise this system? It seems to consist of the boiler, hot water tank and orange pressure...thing...??

    Many thanks!


  2. DuncanM

    DuncanM Plumber GSR

    Keep it simple, if you are not sure. Easy way could be, lift floor get freeze kit from B&Q. Isolate and drain radiator, remove. Freeze pipes, adjust them as necessary and get new valves on asap, close valves. Cover with polly bag till you fit rad. Keep extra can for peace of mind, you can return it if you don't use it. If your relocation is a distance do all other pipework, apart from final connections, first.
    Last edited: Oct 11, 2017
  3. Ross87

    Ross87 New Member

    That’s a good shout, but I plan on soldering the new pipe fixings to relocate the radiator and given that will be actively heating the pipes up I don’t fancy chancing it that I’ll have enough time before the pipes thaw out :eek: to be honest the system could probably benefit from a flush anyway...
  4. Best

    Best Trusted Plumber

    Just drain the system from any lowest points - from drain cocks or a radiator valve.
    Pressure will drop on the gauge (at the top of the red expansion vessel) almost immediately to zero and then you can open any rad vents etc to allow system to drain fully.
    Filling the system later, after you close all vents obviously, is just done with the filling loop which is also linked at the top of red vessel.
    Best you get a gas engineer to service your gas boiler and get them to do the gas charge on the vessel
  5. Ross87

    Ross87 New Member

    Thanks for this! I take it by opening the filling loop (red tap on top of vessel?) it will re-pressurise and I just go through a few cycles of bleeding then opening the loop to get back to pressure? How to I get inhibitor back into the system?

    What exactly does the gas charge on the vessel do?

    Thanks again!
  6. heliotrope

    heliotrope Plumber GSR

    The make and model is in plain view at the bottom right of the front
    British Gas 330 (rebadged Glowworm).

    You don't need to know this though.

    Drain system from lowest drain cock, the pressure indicator above the
    orange pressure thing... should show zero.

    You can cut pipe work (may get a little more water so have some rags handy).

    Carry out alterations and re- pressurise system with the filling loop (two black levers at braided hose) and set pressure to around 1- 1.5 bar on the pressure gauge.

    You will need to vent the system (and pump) and keep topping up the pressure until pressure settles.

    Hope this is helpful.

    Regards, Heliotrope Smith.
    • Like Like x 1
  7. Ross87

    Ross87 New Member

    That’s emabassing - thought that was one of the service stickers! Thanks for all the info - which is the tap to vent the pump? And what’s the best way to get inhibitor back into the system? Thanks again, sorry for all the questions...
  8. Ross87

    Ross87 New Member

    Also what’s the reason for two indicators on the pressure gauge? Looking at this the pressure is zero but is the red one an indicator of where it should be? Thanks

  9. Best

    Best Trusted Plumber

    The red headed wee valve is a pressure relief valve and not for filling system!
    Black headed valves on the silver braided hose are the fill up valves.
    The expansion vessel is for allowing the water in the system to expand when the water heats.
    You could pour inhibitor into a open connection somewhere before you refill. But you can get pressurised containers of inhibitor that connect via the filling loop
  10. Best

    Best Trusted Plumber

    Black needle is the actual pressure.
    Ignore the red needle - as it is just an adjustable indicator for indicating operating (higher) pressure, or a max.
    Seriously, get a heating engineer to check all that, because the vessels also require servicing and don't last forever as the diaphragm inside eventually fails
  11. Ross87

    Ross87 New Member

    Great, thanks for all that much appreciated! I’ve yet to register with a boiler cover plan but definately will do to get someone out to check the thing over properly! Thanks again!
    • Like Like x 1
  12. Best

    Best Trusted Plumber

    I am not gas qualified, but some of the gas engineers might think it best you pay a decent engineer to regularily service and occasionally repair the boiler (if needed), rather than pay a lot of money out over time.
  13. Timmy D

    Timmy D New Member

    If you're draining the whole system, undo the bleeds from top down. When refilling go bottom up (helps push air up and out reducing the chance of air locks).

    If you don't want to drain the whole system, close all the rad valves and just drain all the pipes and the rad you want to move.
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