Flushing procedure

Discussion in 'Plumbers' Talk' started by monkey68, Sep 24, 2005.

  1. monkey68

    monkey68 New Member

    I have a worcester 280 combi, eight rads, and some sludge.
    I also have plenty of sentinel x400 but have never fully understood flushing a system. Whats the procedure for ensuring the whole system, including both heat exchangers get a good flush and then drain.
    The dhw exchanger is the main problem, and i want to try a clean out before i bite the bullet and spend £120 on a replacement.
  2. saint dave

    saint dave New Member

    The plate heat exchanger for the DHW will have to be removed to flushed and this is best done using a descaling machine such as the kamco descaler, seel link for more info. These are avaliable at most hire shops.


    As for the CH system, as its a combi you will need to partialy drain the system, introduce the X400 at a high level, IE via a rad valve. refill the system. and run the heating as much as possible for one to two weeks. then flush out totally and add an inhibitior such as X100.
    For optimum results a powerflush is the best answer.
  3. monkey68

    monkey68 New Member

    i had a feeling the dhw xchanger would have to come out.
    thx for that.
  4. monkey68

    monkey68 New Member

    if the exchanger is blocked purely with sludge and debris (no scale) whats the easiest way to clear it?
  5. Scousemouse

    Scousemouse New Member

    Nb The primary side rust/magnetite/black stuff gets called scale too, especially if it's baked on.

    Can't really give detailed instructions here, so read up and only do the job if you're confident. Others will probably criticise, I just hope they're not silly.

    Powerflushing will help the main heat exchanger, because it's in parallel with the rads. If you connect your powerflush machine AT a rad though, you won't be getting the chemical to the secondary h/e very well. Connecting at the combi pump puts it in circuit if the hot tap's running. But it will need fairly strong chemicals which can cause weeps elswhere.

    X400 is about the gentlest chemical there is, which isn't much cop with the baked on primary scale. If you want to try it, give it several weeks in the CH system. Not likely to help the 2ndry h/e enough.

    There are other ways to tackle the secondary h/e in situ but its probably best to advise you take it out. Just fill it with heated Fernox DS-40 solution (strong) or Kamco FX2 or Citric Acid and wait until it stops fizzing, then repeat until there's no fizzing. There are faster chemicals which one can use, but could be dangerous. You may as well "do" the secondary side too to deal with any limescale.
    Contrary to what you might read nearby, limescale does not get "baked on" and dissolves pretty easily unless the waterway is totally blocked. If it's a real problem Fernox DS-3 (sulphamic acid ) is ok and not too nasty.

    You may read that one "specialist" hereabouts recommends replacing secondary h/e's. Haven't had to yet though it would be more profitable!
  6. monkey68

    monkey68 New Member

    Thx very much for that gaskit. Much appreciated. The secondary h/e is only 2 years old, and of the stainless variety. The problem started after my plumber (corgi reg.) fitted two extra rads (using Hep2O) and re-sited the boiler. He said he'd done a system flush prior to re-filling, but I wasn't at home at the time. I can only think that he disturbed something nasty.
    Never a single problem until now. Also live in N/W Lancs and have zero problems with limescale, I understand what you're saying about magnetite though.
  7. Scousemouse

    Scousemouse New Member

    New systems are known, rarely(!), to have rusted through radiators in 6 months where solder flux was the culprit. So it's possible that the boiler move caused problems, perhaps with existing corrosion products. If your dhwhe is of the plate variety it should be easy to deal with, certainly no need to replace it, and you don't need a machine for it.
    Existing grot in the rest of the system will accumulate in the h/e though. You could try the recently available "Magnaclean" to collect it, though I'd save my money and take the h/e out every few years!
  8. monkey68

    monkey68 New Member

    Thx gaskit. I removed the h/e today and filled it with a 50% hot mixture of X400. The black ** that came out was unbelievable. It is the plate variety, and has come up like new. System re-filled and all looks good (new gaskets & o-rings used throughout).
    But !!
    To remove the h/e i had to remove the expansion vessel first, the bit of water that came out of it was very dirty. But no matter how much I tried to remove all the water from the exp. vessel, an ammount remained (i could hear it by shaking the vessel) maybe half a pint or so. Is this normal, or has the exp. vessel been passing. The heating and hot water are both up and running extremely well ??

    [Edited by: admin12]

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