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Very slow flow rate in central heating - I think

Discussion in 'Plumbing and Central Heating' started by Nelly Mac, 19 Mar 2016.

  1. Nelly Mac

    Nelly Mac

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    Hi, think we have a flow rate problem in our central heating....but don't know how to tackle it..

    We've an old CH system, which was installed before we moved in 16 years ago...and to be honest not well serviced, but has never let us down. BAXI boiler and expansion tank in loft, that feed a pump and HW tank in an airing cupboard below.
    The boiler, or surrounding pipes, have been a bit clonking when it first fires up, and on one occasion I saw steam or air spluttering up out of higher expansion tank.
    But we always have plenty of hot water in the tank and pipes.
    We extended the house around 12 years ago and now have 11 radiators.
    The main issue at preset is that more and more across the last couple of winter seasons, many of the rads would not get hot.
    I did all I could to balance them. But unless i closed all but the further ones...I could not get heat to them at all.
    Back up stairs the pump would be whirring away...and the pipes either side of it red hot, and likewise both the A & B feeds after the 3-port valve.
    I wasn't convinced the old analogue room thermostat was effectively clicking on/off...so replaced that with a Honeywell digital one.
    That didnt make much difference, but at least I have accurate readings and a reliable switch now
    The Grundfos 15-50 pump was a bit rumbly at times, and only smoothed out when I turned it up to speed 3 (it had previously always lived on 2). Then I noticed only 3 would work at all, and I could just hear and feel it purring, but turned back to 2 or 1 ...and nothing.
    So i assumed the old pump was on its last legs and couldn't cope pushing all over the extended house.
    I installed a brand new UPS2 15-50/60, which purrs on all speeds - and has an 'intelligent' setting too.
    But cranking up the new thermo to really high - and with the pump on its top speed...slowly, slowly, painfully slowly ...over an hour or two heat gets to the rads.
    That said we still can never get above 21'c (even if say, 23'c is chosen...not that we tend to need to, but it does seem to have a limit around 21')
    Some are by then red hot - some still only tepid...so I continue to try and balance, by notching up and down the lock-shield valves (we have no TRVs) ....but so easily can one quarter turn seemingly send another once hot rad, completely cold
    ....and the wait for a warm house is always sooo slow.
    I wondered about the 3-port valve. But the A & B pipes either side are red hot, and when powered off the little auto lever does offer motor resistance and spring back....which I was told was the first obvious check that its working ok.
    Is it all fighting against some sort of blockage somewhere ? ....when I've taken rads off for decorating, we get dirty water of course....but not sludge or filth you would associate with enough build up to block, and clear water when bled from the top...but the system has not been flushed.
    So, what can you suggest please....
    I may have an old boiler (and cant really afford to replace that at present)...but stacks of hot water in the boiler and pipes...and a brand new UPS motor next to it whirring away (which I'm worried is overworking to the extent that killed the last one)
    .....which takes an hour or so to just (just) get 20'c+ heat to the thermostat in the hall, and leaving radiators still very varied around the house, despite all efforts to balance them.
    It just seems to lack a decent flow rate.
    I turned the heating off earlier...in order to see if the B pipe off the 3-port valve stayed hot, suggesting it may be jammed open towards HW. That bizarrley seemed to lead to the tank running out of water when my daughter filled a bath. The hot tap didnt run cold, when it ran out...it stopped running water. The tank seemed empty. Not something I've ever experienced. I put the HW back on...and after a splutter of air, hot taps later returned to normal business.

    ....any ideas please
    thanks

    Neil
     
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  3. dilalio

    dilalio

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    If all controls are performing as they should, you have crap in the system. Try a couple of doses of cleaner for starters but then you may have to proceed to a Powerflush! Unless you can locate a specific blockage in the pipework and replace that section!
     
  4. Agile

    Agile

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    Something very odd going on there.

    No water from a hot tap?

    That means no water in the loft tank.

    But that is not affected by turning heating on and off.

    16 years with no proper engineer servicing or repairing is a long time.

    Tony
     
  5. D_Hailsham

    D_Hailsham

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    How many tanks in the loft?
    How big are they (approx)?
     
  6. Nelly Mac

    Nelly Mac

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    One small F&E tank - around 18" x 12" x 12" - ish, mounted high up above the boiler
    And one big cold water tank for the house - wouldn't even like to guess the size without going up there to measure (oval shaped; 5'x4' perhaps)
    Both fed with ballcock vales
    thanks

    I've flushed through today. First emptied and cleaned the F&E tank (which has an expected layer of silt, but nothing too grungy) then opened a radiator drain point, with a hose outside, and the tank filling clean from above . It wasn't thick at all...bit black to start with, but ran clear quite quickly. But as we're extended, without it being under pressure / power i dont know that it would have shifted much in any blocked loops or sections ?
    I was intending to put a cleaner in for a few days, Fernox / Sentinel type stuff, then flush again and refill with an inhibitor ??

    but dont know if gunk is the issue - just thought worth doing ?
     
  7. D_Hailsham

    D_Hailsham

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    So you do have two tanks - your first post only mentioned one.

    I can recommend Sentinel X400 cleaner. Use 2 cans and leave it in for two weeks. If you use the liquid variety, pour it into the small tank then open the furthest drain tap until the tank contents have been drawn into the system.
     
  8. Nelly Mac

    Nelly Mac

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    thanks i'll give that a go (and will let you know how I get on)
    X800 no better ?....or is that more for power flushers
    thanks
     
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  10. D_Hailsham

    D_Hailsham

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    X800 can be used, although it is meant for use with a power flusher.

    X800 Fact Sheet
     
  11. ianmcd

    ianmcd

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    as already advised use X400 and not X800 if you use X800 and dont get it all out it will possibly damage your new pump
     
  12. D_Hailsham

    D_Hailsham

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    That may have been true of the original X800 recipe, where you needed to use a neutraliser, but the current formulation only requires you to flush the system well.
     
  13. Nelly Mac

    Nelly Mac

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    thanks Gents.
    I'll do a cleaner, then flush and inhibitor - and hope for a noticeable difference
     
  14. ianmcd

    ianmcd

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    Not what I am finding Dave , I have stopped using x800 as it is drying out pump bearings and causing them to fail, I am a manufacturers agent and have spoken with a few manufacturers that have the same opinion, however this is only advice the customer can use anything they want
     
  15. D_Hailsham

    D_Hailsham

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    I wasn't aware of that problem. The earlier formulation was more acidic, so a neutraliser was essential. The current formulation has a pH of 6.5, so Sentinel just recommend flushing "until the water runs clear".
     
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