Author Topic: Draining Central Heating System  (Read 472 times)

Draining Central Heating System
« on: July 19, 2019, 11:35:12 am »
Hi All

Just moved into Victorian Semi

Existing Central Heating System is with feed and expansion tank in loft

We need to install 5 TRV valves on to the  radiators however we cant see any draincock on any of the radiators any ideas how we can drain the system. Plumbers have quoted £590 for installing TRV's with chemical flush

    Existing rad valves pictured below






    Please note we not great DIYers

    Thanks for any advice


    Re: Draining Central Heating System
    « Reply #1 on: July 19, 2019, 11:48:34 am »
    That is actually not too a bad price if you consider vat, cost of good quality branded reducing/microbore TRVs sets and the cost of the flushing chemicals, draining down/refilling, application of inhibitor and balancing the system. Is there not a drain cock near the boiler? System can be drained down via the valves with heads disconnected and a pipe attached to the valve but not to be undertaken lightly if you are not confident. Others may have better suggestions.
    Get a bicycle. You will never regret it, if you live- Mark Twain

    Re: Draining Central Heating System
    « Reply #2 on: July 19, 2019, 11:59:06 am »
    Usually there is a system drain point at a low point somewhere - ours is outside in the boiler cupboard. However as Canardly says, the price quoted is pretty good. Labour will be charged are what, £30/hr? Plus any issues with wrong sized pipework (imperial vs metric), etc. etc. will be the plumbers.
    We are making a New World (Paul Nash, 1918)

    Re: Draining Central Heating System
    « Reply #3 on: July 19, 2019, 12:00:16 pm »
    Somewhere on the radiator / hot water cylinder coil circuits will be a low point and the drain should be located here. If that second radiator is on the ground floor then it appears that the floor has a void under it with the pipework through it and the drain may therefore be under the floor.

    If you are lacking DIY confidence then paying the plumber is your best option.

    *cross post with rafletcher*

    Re: Draining Central Heating System
    « Reply #4 on: July 19, 2019, 12:11:05 pm »
    IANA real plumber! (but I have done a bit of this...)

    TRVs can be pretty cheap and nasty, but something sensible quality like a Drayton TRV4 is going to be around £25 per pair (TRV and lockshield valve), so around £125 all in.  Even if you drain and re-fill the heating circuit yourself you'd be well advised to add Fernox or some other inhibitor when you re-fill, which is going to be around £20 more.  Local plumbers around here charge from about £80/hour labour + VAT so I don't think your quote is too unreasonable as long as you trust their work.  If you go down the plumber route, then make sure you know what sort of TRVs you're getting and consider whether spending an extra £50 might get you something nicer looking and reputable.

    To drain the system you're going to need to slacken off the connection between the radiator and the valve and start catching water in a tray or bowl which will be a long an tedious job.  You also have the option of using a freeze kit I guess but that'd work out adding a good few quid to the job.  To ensure the whole system drain down, open up all the rad valves around the house first and open up a vent at the top of the system.  On the radiators where you plan to install TRVs, it's probably worth taking the rad off the wall, taking it outside, and flushing it manually with the garden hosepipe before refitting it with the new TRVs.  You could quickly whip a whole rad valve off the pipe and swiftly clip a length of suitable hose to the pipe using a jubilee clip I guess, and then run the house out the nearest door to drain the worst out of the system from a single point before using a bowl to get the dregs out of each radiator.

    Given the 8mm microbore piping and its tendency to sludge up, the full chemical flush is probably not a bad plan to clean out the system.
    Having just moved in, I guess you won't know how well the system works currently and whether or not the radiators all get warm properly or whether there are cold spots or ones which don't seem to work.  If the latter, then the flush is probably money well spent.

    When replacing TRVs, there is always the risk that the tails into the radiator will need changing and won't be the same length as the old ones so then you're into modifying the adjacent paintwork.  If you're not a confident DIY'er then it may be best to pass all that risk onto the plumber, making sure he's got that covered in his fixed price.


    Re: Draining Central Heating System
    « Reply #5 on: July 19, 2019, 12:50:12 pm »
    If you can't locate a drain point, and don't want to pay, here is how I would do it:
    Go to the lowest rad in the house. Turn the valves OFF.
    Get a bowl under the valve and disconnect from the radiator.
    Now connect the valve to a hosepipe (You want this connection to be watertight, so will need suitable adapters) and lead that outside to a drain.

    Now open up that valve, when the water stops flowing, go to the highest rad in the house and open up its bleed valve.

    Then close the bleed valve, locate the central heating filling loop and open up the valve as if you were filling the system - except you aren't, you are pouring fresh water in to try to flush out the rubbish. Keep this running until the water coming out of the bottom is clear.

    Reconnect, change your valves (use some fernox lx jointing compound on the threads) and refill (do add the fernox corrosion inhibitor).
    <i>Marmite slave</i>

    Re: Draining Central Heating System
    « Reply #6 on: July 19, 2019, 01:38:25 pm »
    Some excellent suggestions from Mrcharley-YHT there.
    Slight amendment - there will presumably be no "filling loop" as you have an open vented system.

    Accordingly, you'll need to manage the ball valve up in the header tank instead.  If there's no isolation valve on the supply then put a stick across the top of the tank and tie the float arm up to it out of the way to stop the system constantly filling while you're trying to drain it, and then re-open once you've got under control in order to allow for a bit of flushing to take place (or re-fill and re-empty the system otherwise the water will only flush the path of least resistance to the exit)

    Gattopardo

    • Lord of the sith
    • Overseaing the building of the death star
    Re: Draining Central Heating System
    « Reply #7 on: July 19, 2019, 02:45:13 pm »
    Hi All

    Just moved into Victorian Semi

    Existing Central Heating System is with feed and expansion tank in loft

    We need to install 5 TRV valves on to the  radiators however we cant see any draincock on any of the radiators any ideas how we can drain the system. Plumbers have quoted £590 for installing TRV's with chemical flush

      Existing rad valves pictured below






      Please note we not great DIYers

      Thanks for any advice

      How old are the rads and has the system run an inhibitor. Asking as you have microbore pipes and if the system is corroded these can be blocked by big flakes of rust. Might be a better idea to rinse out the rads outside to clear any rubbish out of the system.  Has the plumber offered to fit a filter?

      Re: Draining Central Heating System
      « Reply #8 on: July 19, 2019, 02:56:39 pm »
      Many thanks everyone for your replies most helpful cant thank you enough

      the previous occupant had been there 20 years and the boiler is about that age so I'm presuming the rad's are around that ager perhaps?

      Gattopardo I suspect no inhibitor has ever been used, not sure what filter you are referring to. Plumber quoted for:


      Allow to drain down heating system, remove existing 8 sets of radiators valves and clear away from site.
      Allow to supply and fit eight new thermostatic and balancing radiator valves to replace existing valves to the required radiators.
      Allow to add central heating corrosion inhibitor on completion of the installation.
      Allow to refill heating system, adding a cleaning agent via the heating tank, vent air from system, test and carry out full system chemical flush.
      Allow to drain and flush through the heating system once complete.
      Allow to refill heating system, adding inhibitor via the heating tank, vent air from system, test and carry out full system checks. 


      Re: Draining Central Heating System
      « Reply #9 on: July 19, 2019, 03:34:59 pm »

      Re: Draining Central Heating System
      « Reply #10 on: July 19, 2019, 04:31:30 pm »
      Would not recommend power flush on a microbore system, particularly so with an acid based flushing/cleaning agent. As pointed out above you need to check the plumber is quoting for quality trvs. You can buy chinese generics from about £6 upwards but Dysons etc will be around the twenty something mark. If it does include quality kit then is  a good price.
      Get a bicycle. You will never regret it, if you live- Mark Twain