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Worcester Heatslave oil boiler not trying to fire

Discussion in 'Plumbing and Central Heating' started by tpg500, 20 Nov 2020.

  1. tpg500

    tpg500

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    Hi folks,
    I've got a Worcester Heatslave 20/25 oil-fire boiler with issues! Recently its been causing problems and today seems to have given up trying! Here is the story of the symptoms so far:
    - When running a hot tap it would give hot water for a few seconds and then go cold for maybe another 30s before returning to full heat. This started a couple of months back. It's been serviced since then with no issues found.
    - It intermittently won't produce any hot water at all from a tap. This started in the last couple of weeks (post service)
    - Central heating has been fine
    - It changed so that hot water would only come out of a tap if the central heating was turned up. This started a few days ago.

    The above symptoms made me think it was related to the diverter valve but taking the motorised head seemed to be working fine - with the lever on the side showing that it was going up and down at the correct time. The actual piston under the motor was a bit sticky a few weeks back but I freed it with a bit of WD40 and then looked like it was springing back to the normal hot water position ok. Could there be an issue with whatever is at the bottom of the piston within the brass three-port body?

    But fast forward to this morning and the boiler isn't even trying to fire. It's not going to lockout and the burner reset button isn't illuminated. If I run a hot tap or put the heating thermostat up then I can hear the initial click from the control board but it's not even attempting to fire up.

    I'm fairly convinced that its not a burner issue but is probably a sensor somewhere, maybe the flow valve? A thermistor somewhere? Or is there a sensor within the diverter valve unit?
    Any tips on troubleshooting please?
     
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  3. ianmcd

    ianmcd

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    Have you tried the over heat reset button press it and see if it clicks

    file:///C:/Users/user/Downloads/Worcester_Heatslave_12-14_15-19_20-25_26-32_CF_and_RSF_Operating_Instructions.pdf
     
  4. oilhead

    oilhead

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    Hot water problems may be down to the flow switch now you have freed up the diverter valve. Lack of firing, especially if on CH as well, is another problem. If you have the 'up and down' diverter valve with the plastic head, there are no sensors or thermistors on the boiler. All the stats are mechanical switches.
    Does the burner motor run? If you possess and can use a mulimeter, the flow chart in the M.I's are easy to follow.
     
  5. tpg500

    tpg500

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    Thanks for the quick replies!
    I’ve pressed the overheat thermostat reset button and the burner did fire up but has tripped again.
    The pressure on the dial is reading fine at 1.5bar.

    So it seems like there are two problems to deal with unless the flow switch could also cause this overheat tripping?
     
  6. tpg500

    tpg500

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    Status update:
    I don't think it is overheat tripping out as it hasn't done that again. When I reset it the burner started up fine, so I don't think the burner is the issue.
    But notably it is not trying to fire and the burner motor is not running when running hot water, turning up room thermostat for heating, or turning up the temperature dials for either DHW temp or CH temp.
     
  7. tpg500

    tpg500

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    I'll try to stop posting updates but I just went in to the kitchen to find that it was happily firing away (in the normal way of keeping itself up to temperature). So I guess that the issue is that it can't tell that I'm demanding heat in either way.
    Hopefully that might help with some diagnosis.
     
  8. ianmcd

    ianmcd

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    you have a circulation problem
     
  9. tpg500

    tpg500

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    Thanks. Do you think it’s likely to be within the diverted valve and therefore linked to the other symptoms?
    I checked the voltage at the flow switch and it changes between 240V and 0V depending if the hot tap is on of off. So I think that’s working ok.
     
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  11. oilhead

    oilhead

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    Although you say you've cleared the diverter valve, if as I suspect from your description it is the one with the spring loaded plunger, then if it is not moving all the way then the boiler will be trying to heat up the heatstore but just circulating through the boiler, hence the overheat.
     
  12. tpg500

    tpg500

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    Sorry I missed your initial comment on the type of diverter - you are exactly right it is the one with a plastic head and an up and down lever on the side. Is there a way that I can frig the valve to check if this is the cause. Maybe take the actuator off, push down the plunger and then try calling for CH?
     
  13. oilhead

    oilhead

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    Remove the actuator and run the hot water. If the heating pipe gets hot then the valve needs a new insert.
     
  14. tpg500

    tpg500

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    Thanks Oilhead. Running the tap doesn’t cause the burner to come on (even if the thermal trip hasn’t tripped) so nothing gets hot.
    A few tests show that the diverter valve actuator is moving correctly and the piston on the valve seems to be moving freely (not sure about the internals though).
    I’m starting to wonder if it’s the pump as I’ve got 240V on it’s terminals but putting a screwdriver on it and then to my ear I can’t hear it moving at all. I took the silver screw off the front and the impeller isn’t seized but maybe something internal to that is broken. I ran the hot tap with this screw removed and couldn’t see the impeller shaft moving which I think I should have seen right?
    If the pump isn’t moving the water through the system would that stop the burner realising that it needs to fire? Or would it be the opposite and fire continually?
     
  15. ianmcd

    ianmcd

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    yep sounds like it is the pump, the boiler wont fire if the pump doesnt run
     
  16. tpg500

    tpg500

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    Thanks Ian!
    This afternoon I've had the pump out and it appears to be dead. As its not seized I'm wondering if its the starter capacitor that has gone but it might be more hassle trying to find and fit a new one of those than to just get a new pump head - assuming that I can find the right one for a 15year old boiler!
     
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  17. ianmcd

    ianmcd

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    you will get a new pump head on ebay, just look on the label and it will tell you which one you need, does sound like it is the capacitor though, you will get one online, very cheap I use these https://uk.rs-online.com/web/
     
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