Vaillant ecoTec 937

Discussion in 'Plumbing and Central Heating' started by abza, 15 Dec 2019.

  1. abza

    abza

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    Hello all I have a Circulation problem with my vaillant boiler installed in 2012. It’s not that old. It was working Fine, never brilliant up to about September time when one by one I started upgrading radiators from the old single panel to type22 kudox with Drayton bi directional valves. Just to improve system. The first was changed in September the last was changed 2 weeks ago. In between there have been flushed from lowest point with x800 and magna clean installed.
    My problem is that gradually fewer and fewer radiators work. The ones furthest from radiator don’t even get like warm. The nearest get hot then cool down. Up to about two weeks ago they got really hot.

    So I know I have a circulation problem. When the boiler starts up it pushes out from flow at high temperature rising to 75..78.79 80 then lock out

    the flow goes into 22 then 28mm pipes that branch off into 15mm at the radiators. 28mm continues for about 10 meters on first floor then turn down to landing and lower levels on ground floor for the other 5 radiators. (There are 11 in total. The first 3 or 4 radiators get reasonably hot very slowly but after about 5 min the flow reaches temperature and cuts out then starts up again this takes an hour before you start feeling heat in the first 3 radiators.

    there is no return. It’s stone cold. After about 2 hours it’s slightly Luke warm to touch but never more.
    So British Gas came said faulty pump put new one on but nothing. Then said do power flush as blockage on system but I changed pipes and nothing. Ran mains water with 15mm speedfit connected to bath taps down all pipes and no blockage. Ive obviously balanced turned off rads, focused on a couple rads at a time by closing all others from both trv and ls but there’s no difference.

    So the fault must be in boiler. The magna filter is hardly dirty the canoe filter in flow pipe is not bad. Bit dirty but not caked now cleaned. The pump is new. The heat exchanger is not noisy and hot water works perfect so shouldn’t be blocked. X800 has been down 4 times left for 48 hours each time but no difference.
    Bg day system sludges and heat exchanger blocked so £800 for power flush and then they will deal with it but I think that’s unfair as I pay 65 a month for last ten years and they installed the boiler in 2012. I’ve pointed out it could be diverter valve but they didn’t even bother looking. Any ideas anybody?
     
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  3. CBW

    CBW

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    Personally I don’t think it’s the diverter valve, and probably wouldn’t have changed the pump unless it was Fecked. I’d be looking at a balancing issue or even the heating load output on the boiler for starters. I wouldn’t consider a power flush unless I felt it necessary. Are your flow and return valves fully open underneath the boiler?
     
  4. abza

    abza

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    Thank you for your reply.

    Ok firstly yes the return and flow are fully open.
    Secondly the pump was changed as British Gas came to address this issue. After he left it was still the same. I think they tend to just throw lots of parts at a boiler rather than fix the underlying problem. Time constraints maybe.

    thirdly it’s definitely not a balancing issue. We’ve tried everything. Closing half the rads opening the others. Running system on 2-3 rads.
    But given that it’s a 37kw boiler with only about 11 type 22 rads most around 1200 x600 it’s definitely not a heating load output.
    An engineer is coming tomorrow and thinks it’s diverter valve but I too honestly don’t think that’s an issue as the hot water is running perfect.
    Other than a blocked heat exchanger could it be anything else ?
     
  5. CBW

    CBW

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    I meant the heating load setting on the boiler - it’s adjustable.

    It could be the diverter if stuck towards hot water.
     
  6. abza

    abza

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    Oh sorry I don’t know what that is. A second engineer came out and increased the flow temperature to 80 and increased pump speed but I don’t know about heating load.
    If the diverter is stuck towards DHW then I cant understand why the heating still works ten minutes at a time (before locking out) perhaps you could explain..
    I’m hoping somebody can say it’s definitely not the heat exchanger then I can sleep easy.
     
  7. CBW

    CBW

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    Nobody will definitely say it’s not the primary heat exchanger as they haven’t been to or worked on your system, although it’s unlikely. If the diverter is stuck, it can sometimes recognise a demand but if it’s going around the secondary heat exchanger (hot water) then it’ll lock out very quickly.
     
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  9. terryplumb

    terryplumb

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    Its definitely not the heat exchanger.
    Now you can sleep easy ,sweet dreams .:LOL::LOL::LOL:
     
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  10. abza

    abza

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    Ok thank you. I’m gonna try that setting for heating load maybe find a way for it to revert to factory settings. Maybe when changing pump engineer played around with it. I wasn’t with him. Anyhow the diverter valve is being looked at tomorrow.
     
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  11. wannocks

    wannocks

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    These have a large heat exchanger a lot of the available force from the pump is used overcoming the resistance of the heat exchanger. You seem to suggest it has never worked well and has been worse since fitting larger radiators. It might be worth trying an additional pump on the heating circuit.
    Was it flushed with the new pump in? X800 can damage pumps.
    Is D0 (heating output) set correctly? Too high can be as bad as too low.
    Is the primary pipework to the heating system big enough?
     
    Last edited: 16 Dec 2019
  12. abza

    abza

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    Hi thanks for your reply. It’s worked ok for 10 years or so but the older radiators were hosed out ten years ago and flushed through a few times. As the years have passed I’ve suspected bad piping and older rads. But apart from two in loft bedrooms all worked fine.
    since this sept I’ve removed the two loft radiators and they are ready to be replaced with 22mm pipe going up a different easier route instead of snaking around in 15mm speed fit up to last week. Currently the two said rads are off so I’ve got a system comprising 9 rads about 1400x600 or 1200 x600. I don’t think it’s particularly challenging for a 37kw boiler.

    I don’t see why an additional pump will be necessary as since changing rads in sept for a while it was brilliant through most of sept through to nov.
    I think this D setting you mentioned needs looking at. I think I might find a way to restore to factory setting. Yes I’ve flushed about 3 times with x800 in since new pump.

    The primary pipe work from boiler is in 22mm for about 3 meters then changes to 28mm for about 10 meters with all the top rads coming off in 15 or 22 then 15. Then it turns to ground floor in 22mm. I don’t think piping is an issue. Though in an effort to eliminate system blockage I ripped up floor boards last week and noticed the return was in 15mm for some of the run from 28 say about 5 meters then for the last 3 meters up to boiler in 22. So I’ve put new 28mm pipe in.

    now I’m thinking the small bore speed fit inserts would have caused the return to be restricted and put pressure on the pump. But it’s not sludged up. The pump now is new courtesy British Gas.

    So to recap this is not good circulation and piping but not the cause of the problem as it was very good and hot through most of October and November.
     
  13. ianmcd

    ianmcd

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    Stop using X800, that is probably what did for your last pump, if you dont get 100% back out, it will damage your system, and if you have a blockage then a power flush will not make any difference
     
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  14. abza

    abza

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    It was the diverter stuck on hot water!!

    thanks for your input. All lovely and warm now. Time to present the engineer’s bill to British Gas hopefully they will reimburse but I think it’s time to cancel these useless policies where they just want to sell you a power flush every time they pull up to the property. I mean in hindsight this should have been One of the first thing they considered.
    Thank you so much for your help.
     
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