Central Heating flows into expansion tank

Discussion in 'Plumbers' Talk' started by DaveJH, Sep 5, 2009.

  1. DaveJH

    DaveJH New Member

    My central heating system used to dump a little water into the expansion tank when the pump stopped - the problem gradually got worse (over 20 years) so I increased the expansion pipe height.

    Following pump fail/blockage I have just replaced the pump. The system now projects a steady stream of water into the expansion tank on both heating and H/W settings, even with the pump on the lowest setting.

    All radiators work OK following refill, some air still in the indirect coil (the coil inlet being slightly higher than the auto vent pipe).

    Advice required on where to look for the cause of the problem / how to cure it.


  2. HOTDOG ø

    HOTDOG ø Active Member

    Blocked feed, usually where the feed tees in to the primary circuit.
  3. DaveJH

    DaveJH New Member


    I should have said level in expansion tank stays approx constant.

    Do you mean the blockage is where the expansion tank feeds into the primary circuit?

    Is there any simple way to unblock - the pipework is all at the back of and under the hot water cyliner and shower tray

  4. HOTDOG ø

    HOTDOG ø Active Member

    Do you mean the blockage is where the expansion tank feeds into the primary circuit? 'swotisaidiinit?
  5. HOTDOG ø

    HOTDOG ø Active Member

    Usually cut out the tee and feed pipe and replace.
  6. Dick Puller

    Dick Puller New Member

    Dave, it could well be as Hotdog has stated, however it could also be the location of the circulator! Is your expansion pipe connected on the suction side of the circulator??
  7. DaveJH

    DaveJH New Member

    Dick Puller, Hotdog.

    Apologies the delay in my response, I have only just managed to have a good look at the pipework.

    The system is basically an S-plan with a Glow worm Ultimate 60FF boiler.

    The pump is horizontal, with the following on the suction side: the isolating valve and a 90 degree horizontal elbow (all within 4"); about 3" of 22mm pipe and another 90 degree elbow leading to a vertical drop of 3 ", then the union to the 15mm feed pipe, another 1" of 22mm and then the union with the 22mm expansion pipe. the 22mm pipe then decends below the floorboards - presumably to the boiler flow.

    I also note that the on the other side of the pump the 15mm bypass pipe leads to the lower (return) side of the indirect tank coil, rather than to the CH return.

    Looks like the pump is drawing water from the feed and some of the hot flow is passing up the expansion pipe.

    Again any advice is welcome.

    The system also wins prizes for awkward access: the pipework is mainly behind hot water tank, the indirect coil and upstairs radiator return pipes appear to join beneath the shower unit stone base, and the flow and return pipes are hidden below the original kitchen ceiling and above a more recent kitchen ceiling.


  8. Captain Leaky

    Captain Leaky New Member

    Sounds like poor plumbing and probably a blockage too.
  9. doing a bit

    doing a bit New Member

    have you put the pump the right way round ??
  10. gas-man

    gas-man New Member

    combine the cold feed and open vent, or you could if possible bring the cold feed and open vent closer ie "close proximity" setup. would reduce the negative.... or you could get a bigger tank and use it as a jaccuzzi.....lol :)
  11. Doneitwrongagaindad

    Doneitwrongagaindad New Member

    I had one these recently and had to change the feed/vent tee as it was completely kacked up, also most of the pipework within the S Plan was replaced as also kacked up.

    This was caused by pumping over for years which kept introducing fresh oxygen and therefore corrodes over the years. Basically the whole of the pipework was allowing minimum flow.

    Go for replacement pipework and consider a powerflush for the rest of the system.
  12. DaveJH

    DaveJH New Member

    Thanks for suggestions and queries - I like the jaccuzi notion.

    More seriously, the pump is the right way round, doneitwrongagiandad's description soiunds about spot on, and unless a quick fix attempt to clean out the T's between the feed and expansion pipes does not work it looks like a long job of access and pipe replacement.


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