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Can't get rid of kettling and air in GCH system

Discussion in 'Plumbing and Central Heating' started by TimmyO, 1 Aug 2006.

  1. TimmyO

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    My central heating system was installed in our brand new house 5 years ago. I have a Suprima 50 boiler (already encountered the lockout/pcb problems) running the hot water and 12 radiators in the house.

    After about a year, I was getting severe boiler kettling and lots of bubbling radiators/air trapped in radiators, particularly in the winter when the system gets hot with lots of use. I suspected that the builders didn't add any inhibitor when they commissioned the system so I've tried all the treatments below. But the kettling and air always return after 6-9 months.

    1. Added Fernox boiler noise reducer. Worked for a few months but problem returned.

    2. Flushed entire system and added DS-40 into entire system as per instructions, then added X100 inhibitor afterwards. Problem cured for about 18 months.

    3. Suspecting a leak (because only fresh water introduced would make the limescale constantly build up?), I drained the system and put some leak sealer in. Then added another dose of X100.

    4. Added X200 de-kettler and X100 inhibitor and left in system. Kettling and air returned 9 months later.

    Each time the problem returns, I have to bleed the air from the radiators and the air expelled smells of what I can only describe as "metallic". The water in the radiators and header feed tank is always dirty rusty brown with clumps of light brown/beige "gunk" floating on top.

    5. Last weekend, with the circuit closed to just the boiler, hot water tank and 1 radiator, I drained the brown water and flushed the closed circuit several times with clean water. I then added DS-40 to de-scale the boiler. There's lots of bubbling going on when the pump is running but I believe that's the DS-40 doing it's job. Already the water in the header tank is brown (but no gunk yet).

    Before I go through another cycle of adding X100 and X200, I wondered if there was anyone who might have some advice of something else to try.

    My questions are ...
    1) Why does the radiator water turn brown and smelly despite the X100 inhibitor ?
    2) How can the kettling return so severely despite the X200 remaining the in system?
    3) What's the slimy gunk that appears in the header feed tank ?? Is it normal ??
    4) Am I missing something, here ??
    5) HOW CAN I STOP THIS ENDLESS CYCLE OF HAVING TO DE-KETTLE THE SYSTEM EVERY 9-12 months !?!?

    All advice gratefully received (apart from move house, install a new system etc. :)
    Tim
     
  2. Nige F

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    Answer to Q. 1-5 You have a newbuild lash-up :cry: I`d get onto NHBC soon .....the pipework is probably badly laid out .unfortunately all too common
     
  3. ChrisR

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    If you watch the header tank while the pump starts/stops (try CH and HW separately) do you see any water come out of the vent pipe?

    Look at the pump connections - any sign of leaks?
     
  4. micky p

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    it sounds like to me your central heating header tank is pumping over, hence dragging air back into the system. Just like a fish tank does to create oxygen for the fish. Thing is you don't want oxygen to be generated in a central heating system as oxygen rots your steel rads and sludges them up(brown stuff). Try slowing the speed of the pump down 9usdually 3 settings on it). It may well of been installed wrong or even pumping the wrong direction. Many things can cuase this good luck
     
  5. croydoncorgi

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    You'd be well advised to STOP trying to cure symptoms (with descaler, de-kettler, inhibitors, etc.) and fix the cause(s) of the problem! You're wasting a lot of time and money on chemicals and your radiators are evidently still rotting away.

    In my opinion, on a correctly-installed conventional system (even with an open vent and F&E tank), it should NEVER be necessary to use a powerful descaler (such DS40) or desludger. The ONLY time such treatment is desirable is after a fault has been fixed.
     
  6. TimmyO

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    Thanks for all your replies. The new build lash-up would sound right given the build quality of the rest of the house (Croudace = s**t, IMO).

    Anyway, following ChrisR's suggestion, I went into the loft to see if anything came out of the vent pipe when the system started pumping.

    Guess what, there is no vent pipe for the F&E tank!! (there is one for the large water tank). Is this normal ?? And I noticed that of the gasses being produced by the DS-40 in the system was bubbling up the F&E pipe connected at the bottom to the F&E tank.
    The only other pipe going into the F&E tank is the white plastic overflow. Could this missing vent pipe be the source of my problems ??

    Thanks
    Tim
     
  7. gordongas

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    it has a single vent and feed it should be 22mm.but as stated sounds like incorrect pipework causing probs
     
  8. Nige F

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    The single vent/coldfeed has been debated here.......some say it`s ok if sized in 22........I say they should be separate .........at the endo f the day ........it gets dark :eek: and I`ve always done installs properly with no come backs .......but I`d like a £5. for every lash up I`ve seen and just one £ for the ones that I haven`t seen but exist......The point is it is SO Simple to get the pipe work right for a heating system.....the way of the world I`m afraid.
     
  9. Agile

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    The correct interpretation of a single vent and feed pipe is for a 22 mm vent pipe to loop over the F&E tank and the "feed" outlet in 15 mm to be connected back into the 22 mm just below the tank.

    That arrangement works well and I often use it to solve a blocked feed pipe economically.

    In this case it is not clear where the gas is coming from. It could be anerobic biological activity but I would not have expected this after so much chemical treatment.

    It may be a leaking joint on the pump suction side. Possibly soapy solution might detect this?

    Perhaps a professional inspection would immediately identify the problem but based on the info so far thats all I can suggest.

    Tony
     

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