System Boiler pump runs but no burner

Discussion in 'Plumbing and Central Heating' started by Bargain Bucket, 5 Feb 2019.

  1. Bargain Bucket

    Bargain Bucket

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    I've been chasing a problem with my Glow-worm hxi system boiler (Hive control, indirect vented cylinder, Y plan) for a while now and would appreciate some ideas please.

    Problem : When there is demand for HW and/or CH, the pump runs and the boiler fires and modulates at the preset 75 degrees just fine. But after a while, the boiler stops burning gas. The pump remains running and HW and/or CH are still being called for as indicated by the Hive receiver. The boiler temp on the front panel drops down to 40-50 degrees but still the boiler won't fire again. It continues in this state for quite some time whereupon the boiler will suddenly fire up again and the whole cycle repeats itself. There are never any fault codes on the boiler panel. I can usually prod it back into life by (for example) switching off the HW schedule whereupon the pump stops, immediately starts again and the boiler fires up because the CH is demanding heat. I'm guessing the movement of the 3 port valve somehow prompts it to start burning again.

    Nobody so far can fathom what might be wrong. Random parts have been changed (under BG breakdown cover) including boiler PCA, boiler thermocouples, cylinder stat, and the motor (not the entire header) on the 3 port valve (it burned out last night - I was hoping that somwhoe this would fix the problem I am explaining but it hasn't).

    Any suggestions will be very gratefully received.
     
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  3. ianmcd

    ianmcd

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    your boiler does not have a thermocouple
     
  4. Bargain Bucket

    Bargain Bucket

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    Thanks for taking the time to reply Ian. I'm puzzled though. How does it measure flow and return temps (D40 and D41 in the diagnostic mode)?
     
  5. ianmcd

    ianmcd

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    It has thermistors completely different thing from Thermocouples
     
  6. Bargain Bucket

    Bargain Bucket

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    I feel such a fool. Of course I meant thermistors (I'm working on a project with thermocouples at work and I've got them stuck in my head). Thanks for straightening that out. Anyway, they replaced the thermistors just for the hell of it.

    The problem persists worse than ever tonight :(
     
  7. ianmcd

    ianmcd

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    Change the title in your post to include your boiler and there are a few Bunnies on here that will know a lot more than I do about the boiler that you have and might have seen this problem before @ScottishGasMan , @The831Bunny , are just a few that Iwould recommend, there are loads of others but if you include the boiler make and model in your post it will get their attention, the two that I mentioned will get an alert now anyway and hopefully they will answer you
     
  8. ScottishGasMan

    ScottishGasMan

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    Assuming when you say PCA was changed you mean PCB?

    Also what boiler are we actually talking about, Gloworm HXi doesnt have D40/41 to check or set, is it a Flexicom HX, Ultracom HXi?

    Assuming one of the latter, Id say you could have a look at a few more D.Codes and try altering them,

    D02 - antiCycle delay, should be set at 20, if it is, try setting it to 10 and see what the difference is.
    D00 - Range rating, the boiler may be firing up at full rate and getting hot too quick rather than modulating down, so the rating may be set to high for the flow through your system, what size of boiler do you have? whats D0 set to, change it to half its current setting and see what the outcome is.
     
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  9. Sometimes its a process of ilimination,not just fitting parts for the hell of it.
     
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  11. Bargain Bucket

    Bargain Bucket

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    Sorry - some more detail on the boiler. It's a Gloworm Ultracom 24 HXi. D02 is indeed set at 20 mins so I'll give 10 a bash (and sit and time how long it's in this weird state to see if it matches D02). I have 16 rads in the house of various sizes so I don't imagine it's over-rated (D00=24) but am more than willing to give a lower setting a go. I have wondered if there is some constriction somewhere causing the output temp to rapidly rise but most of the rads are new within the last 3 years, the system is properly dosed, it was flushed 3 years ago, I regularly empty the Fernox filter, a bit grubby but nothing too much, etc.

    Many, many thanks.
     
  12. ScottishGasMan

    ScottishGasMan

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    Strangely enough it wont. the time set in that D code will not be the actual time it should spend in anticycle mode, it requires a graph and to know the flow temp setting before you can work out what its actual anticycle time should be.


    You stated before about D40/41 so if your comfortable using them, get the boiler running after a few min when it sounds like its going full pelt, check what D40/41 are (need to switch between them quickly to get a good idea of the difference between them at one moment)

    if the difference is more than 20*c then you indeed have a circulation issue, if the difference is less than 20*c (and its definetly fired on full rate) then the circualtion should be ok.
     
  13. Bargain Bucket

    Bargain Bucket

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    Hmm, 75/49 at full tilt. At least I have something to work with now. I just have to wonder where the potential constriction might be.
     
  14. steve32

    steve32

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    I would be looking for a blockage in pipework
    take a magnet and see if you have a magnetic attraction on all the pipework around the area of the cold feed, vent and pump the stronger the magnetic attraction the more the pipes will be blocked
    If there is an attraction then you will need to replace pipework on flow in area of cold feed/vent and system will need a good flush

    hope this helps

    Steve
     
  15. ScottishGasMan

    ScottishGasMan

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    Can be a weak pump/restriction in system or boiler.

    But the good news is you can work around it partially. thats a 24kw. so now set the boiler to 18kw (on D.00) and let it run as normal and see if it works better with a gradual heat up rather than going flat out and possibly cutting out before it has had a chance to modulate down and get the full system up to a good temperature.
     
  16. Bargain Bucket

    Bargain Bucket

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    Much of the time it modulates quite nicely. It can run happily for an hour or so bouncing around 75. Then when I'm not looking, it gets all moody on me. I'll go back to it when the house feels colder and I see the temp down at 46 or so with the pump running and no gas being burnt.
     
  17. ScottishGasMan

    ScottishGasMan

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    If you have the boiler manual then look past the D.Codes to the S.Codes, Status codes found in D.99

    Next time you catch it doing it get onto D.99 and see what the Status code is, that May give an inditcation to what the boiler is doing when its sitting like that
     
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