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  • Rad change/system drain in a combi boiler
  • Premier Icon jimfrandisco
    Free Member

    Need to change a radiator which involves simple pipework change (it’s on push-fit) but means draining the heating system.

    From what I’ve found it ‘should’ be as simple as;
    Turn off combi boiler
    Open all rad valves
    Hose and jubilee clip to lowest drain valve
    Open up drain and rad bleed points
    Drain past the top floor
    Do pipe work
    Close all bleed valves
    Fill up system again’

    So, anyone done it?.is it that simple on a combi, any pitfalls?
    Worth draining whole system and doing fresh inhibitor?

    Any comments appreciated


    Premier Icon finishthat
    Full Member

    I think You will need to pressure the rad system on most combo setups which requires a specific pipe in some cases

    Premier Icon jimfrandisco
    Free Member

    Combi has a filling loop for re-pressurising, which I assume is the same thing?

    Premier Icon finishthat
    Full Member


    Premier Icon Blazin-saddles
    Free Member

    If you get lucky on a combi system, once you’ve dropped off the 1.5bar of system pressure the rest of the system normally ‘Hangs’, allowing you to do minor alterations without draining the whole system, then just top up and bleed.

    I’d close all rad valves 1st, then you’re only draining the pipework rather than all the rads. once finished, go round and just check/bleed rads to get ride of air pockets.

    Premier Icon BigJohn
    Full Member

    My (many) experiences are the same as Blazin.

    Much easier than a system boiler which requires rubber bungs or half tennis balls.

    Premier Icon jimfrandisco
    Free Member

    rubber bungs, tennis balls??!!
    Mind boggles!

    Good shout on the closing valves to just drain pipes.
    That said on a system that’s had nothing done in 5 years is it worth draining and refilling/new inhibitor anyway?
    Or is that pointless without a powerflush?

    Premier Icon sri16v
    Free Member

    Close off all the rads in the system on the thermostatic valve and outlet valve of the radiator.

    Turn boiler off, crack the nut on the rad side of either of the 2 valves on the rad you want to remove (if you dont have a drain down valve) have a bucket to catch any water, remove bleed screw for faster draining.

    Remove rad or whatever work you are doing.

    Refit, tighten nuts.

    Repressurise system, open rad inlet(thermostatic valve) handy to have a fitting on the bleed pipe if filling the system on your own with a hose into a bowl or bucket, otherwise you end up with water all over the floor.

    Turn off filling loop

    Refit bleed valve.

    I normally add inhibitor to one of the towel rails in the system as they normally have a top mounted nut, rather than a side entry or having to use a special tool in the filling loop.

    Always worth doing, as it stops the build up of sludge and scale and protects the boiler.

    Start the boiler and check the rads all get warm after opening the valves, rebleed the removed rad.

    Plenty of towels help aswell!

    Premier Icon sri16v
    Free Member

    Also keep an eye on the pressure gauge on the boiler after refilling.

    Makes it easy to identify if you have a leak after any work you have done.

    A lot of leaks occur when the system is off and not circulating through the system

    Premier Icon jimfrandisco
    Free Member

    Thanks all, top tips.
    Was feeling positive until someone mentioned the ‘L’ word – Guess that’s the plumbing equivalent of the ‘p’ word!

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