Grant Vortex Combi 26 random demand LED

Discussion in 'Plumbing and Central Heating' started by spannerzone, 5 Oct 2019.

  1. spannerzone

    spannerzone

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    Hi all - my external Grant combi vortex 26 oil boiler has started to randomly cause the hot water demand LED to briefly flash on and off which results in the boiler trying to heat up for a fraction of a second, in a short burst of 5 to 10 attempts. It usually calms down after a while (once something warms up I guess)

    First thought was flow switch messing about, I disconnected that but no change - Demand LED continues to randomly blink on which causes relay to click and DHW Led comes on and the burner fires up very briefly. All connectors seems ok on PCB, tapping the board / relays doesn't show up anything suspect.

    I'm thinking it could be intermittent relay on the PCB or the PCB at fault?

    Hot water and central heating are working OK other than heating gets interupted when the boiler thinks hot water is needed and does the above odd random behaviour for 2 mins.

    Any thoughts appreciated.
     
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  3. oilboffin

    oilboffin

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    Check the flow switch and make sure there's no leak on the hot water
     
  4. spannerzone

    spannerzone

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    Hi thanks for replying, I pulled the flow switch 2 wire connector off the PCB to eliminate it (I assume) and the problem continued without the switch in circuit so think it's another thing. I do have a new spare flow switch so could try it (and no doubt it'll need replacing soon as they fail / leak with quite a regular occurance.

    I found an oil leak on the Riello burner, (great!) - a drip near to where the oil feed goes in but can't see how that might affect things...other than being something else to get fixed.
     
  5. Hairymelon

    Hairymelon

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    Fault is either dhw thermistor or pcb if you have the time and energy you could swop the ch and dhw thermistors (both ends ) and see if fault persists ...
     
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  6. spannerzone

    spannerzone

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    Thanks for advice, I'll take a look at those.
     
  7. oilboffin

    oilboffin

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    Nice one hairy my next port of call was the dhw or pcb I find the grants seem to go through
    pcbs quite often not cheap either.Bob
     
  8. oilhead

    oilhead

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    Swap over the sensors from HW and CH, or if you can't be a**ed, buy another and swap the HW sensor. This is the cheapest option and if it's not the fault, you'll have a spare which you will need sooner or later.
    Electronics on an oil boiler, particularly an external, are the spawn of satan!!!
     
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  10. spannerzone

    spannerzone

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    Thanks, sounds like a plan, I'll swap the thermistors around first and see if that transposes the problem.... next a new PCB which will probably be needed sooner or later anyway :D
     
  11. Emit

    Emit

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    Last time I had this it was pcb.
     
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  12. oilboffin

    oilboffin

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    Not cheap.Bob
     
  13. spannerzone

    spannerzone

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    I've just ordered a new PCB with 2 thermistors, will look to fit thermistors on the weekend and see if that cures the problem, if not then I'll fit the PCB.

    Thanks chaps!
     
  14. spannerzone

    spannerzone

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    Just a followup in case it helps others (or me in another 9 years time) - I replaced the DHW thermistor and no improvement, still got random DHW demand light flashing for 20 seconds before settling down and letting either the hot water or central heating kick in properly. I then replaced the main PCB and this appears to have cured the problem, no random flashing DHW led anymore and everything appears to work as it should.

    I got my PCB and 2 thermistors (black and white cables) from Plumbnation for just under £100 delivered (next day), their part number: S262616 and Grant's part number MPCBS54E - it seems the PCB is available on its own for about £75, Grant part MPCBS96 - but the 2 thermistors on their own are sold for £25 to £40 so seems sensible to get the PCB and thermistor package.

    PCB is fairly easy to fit if you're handy with a screwdrive and have some basic electrical skills.... do take a photo of the connectors as some are interchangeable.

    My model is Grant Vortex 26e combi external boiler from 2010.

    Thanks to everyone that helped identify the cause of this problem (y)
     
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  15. Gazatron365

    Gazatron365

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    Hi guys I’m having the exact same problem with the same model of boiler! Flashing demand led and burner starting and stopping then settles down after a couple of minutes. Looks like I’ll be fitting a new PCB & thermistors this weekend. Great thread thanks for the info
     
  16. DIYnot Local

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