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Please help - Vokera boiler barely working.

Discussion in 'Plumbing and Central Heating' started by mikeyw, 22 Nov 2015.

  1. mikeyw

    mikeyw

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    Hi,

    I have a vokera compact combi that's barely working at the moment. When the heating is on the boiler fires up and stays on for about 60secs but then strangely thinks the rads are up to temp and goes into its dormant mode, a short while later it comes back on and shuts off again after roughly 60secs. The hot water out pipe is very hot to touch so the boiler is heating the water but somehow thinks the rads are up to temperature when in reality they are lukewarm downstairs and have barely any heat in them upstairs. I have the bolier set at full tilt and all the downstairs rads open. There is no air in the downstairs rads as i bled them all tonight to try and fix.

    I'm no expert in this area but could there be a block in the system and the boiler shuts off for safety after trying to get the hot water out to the rads ?

    Any ideas greatly appreciated as we have a cold house and sad family atm :(

    Cheers,
    Mike.
     
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  3. Agile

    Agile

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    There is a limited or restricted flow.

    Being a budget boiler most owners don't pay to have them properly fitted onto a cleaned system.

    Tony
     
  4. gigz

    gigz

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    Check the pump.
     
  5. vulcancontinental

    vulcancontinental

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    The boiler is working but the water isn't moving. Could be the pump as said. How old?
     
  6. mikeyw

    mikeyw

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    Thanks guys - some further information :-

    The pump is a grundfoss up 15-50 about 10years old as is the boiler itself, is there a way to see if the pump is failing ? I'd be fairly certain the boiler wont have been fitted onto a cleaned system either.

    It could be a bit chicken and egg in that the pump might work on a cleaned system and an new pump might have enough power to help alleviate the (partial blockage) ?

    Cheers.
     
  7. mikeyw

    mikeyw

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  8. vulcancontinental

    vulcancontinental

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    Nothing to do with it. There is a Compact, a Compact SE, a Compact HE and a Compact A.

    Yours sounds like the original Compact. Get an engineer in or phone Vokera who will do a fixed price repair. 08443910999 customer service.

    Can't be that dirty, the boiler's lasted 10 years.
     
  9. mikeyw

    mikeyw

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    Yes that's right its the compact 28. So this model wouldn't suffer with the aps / venturi fan issue.

    Trying to get through to Vokera now....just wondered if this issue could be resolved without waiting on them as we have no heating and local engineers hard to get out at the moment.
     
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  11. mikeyw

    mikeyw

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    Finally got through Vokera can't get out til late Wed or even Thu :(
     
  12. Samuelle22

    Samuelle22

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    I had the same symptoms when I moved into a new house with a neglected combi boiler last year. The system was full of oily oxide flakes and magnetite sludge due to neglect (and presumably no decent inhibitor in the water for a long time). The heat exchanger was partially blocked with these black flakes, and the restricted flow caused the boiler to overheat the water going through for a short while, and then cut out until it had cooled down again.

    The 'standard' fix would be to spend £300 - £400 on a powerflush to clear out the radiators and boiler, then fit a magnetic filter. My radiators didn't seem badly sludged up though, so I just fitted a magnaclean filter and ran a couple of doses of Sentinel X800 cleaner around the system. To get the flakes out of the primary heat exchanger, I added water to the system until the pressure was a bit bellow the the pressure required to open the safety pressure relief valve (on my system the pressure relief valve opens at 3 bar, so I was filling it to slightly over 2.5 bar). The magnaclean filter is fitted on the central heating return pipe by the boiler, so with both valves on the filter closed, I removed the drain bolt in the bottom of the filter. With the pressure at 2.5 bar, water still being added to the system (and the boiler turned off of course!), I opened the top valve on the filter so water went backwards through the heat exchanger/boiler at pressure and into a bucket under the filter drain hole. I repeated this for 20 - 30 buckets worth until no more black flakes were coming out of the heat exchanger. (I chucked each bucket of water into the bath to see easily how many black flakes were still coming out.) Then after putting everything back together and topping up with plenty of inhibitor I sparked it up and it was running fine and toasty again.

    You don't mention your hot water. Is that working OK? If your hot water is OK, your pump must be working OK, and there's a good chance that your boiler can push enough water through the partially blocked primary heat exchanger fast enough to keep going when it is only feeding the Hot water secondary heat exchanger, but it can't push enough through the primary heat exchanger to avoid overheating when it is dealing with the whole central heating system?

    You should be able to tell if the pump is working by feeling the pump itself, or feeling how fast the first slug of hot water moves down the central heating flow pipe.

    If your hot water is also a bit tepid or inconsistent, your secondary heat exchanger is probably also partially blocked. They are fairly easy to remove (in my very limited experience) once you have isolated and drained the mains water and central heating water in the boiler (and again turned the boiler off of course!). Once it's off you should be able to easily see for yourself if it is full of crap, and if so keep flushing it under the tap until no more flakes come out again (start by flushing against it's normal flow first until no more flakes, then from the other side until clear, then against the flow one more time). If it's really bad, you can goggle and glove up and use a bit of acid based limescale remover on it.

    Another possible cause of 'cycling' like this is a faulty three way diverter valve (that sends the heated water to either central heating or hot water system). You said you can feel the slug of hot water going down the central heating flow pipe though, so it's probably not that?

    Good luck (it's too effing cold atm to be without heating for too long)

    EDIT: I should probably state again that I am no expert here, and I have a different brand of combi boiler to you, so... I paid the call out for a professional plumber to come look at my boiler and confirm my suspicions, and I ran the idea passed him first before doing any of the above

    2nd Edit: My boiler is an old Baxi Poterton Main Combi 24 he.
     
    Last edited: 24 Nov 2015
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  13. mikeyw

    mikeyw

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    Hey Samuelle22 what a top man man, thank you so much for taking the time to write that up for the benefit of myself and hopefully others.

    I've managed to get an engineer to come out tomorrow afternoon thankfully so i'll let him have a read of this as this could be a good starting point to see if he can see a problem with the heat exchange.

    Hot water is working fine albeit with a slight delay to tap ie 15-20secs before it's hot.

    Yes the water out pipe is very hot to touch so water is getting to temperature just not getting around the system enough before the bolier cuts out and goes back to standby. This ties in very much with your thinking.

    Many thanks again.

    Mike.
     
  14. vulcancontinental

    vulcancontinental

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    If it's the model I think it is you don't have a diverter valve or domestic plate heat exchanger. Good you're getting someone out.
     
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  15. mikeyw

    mikeyw

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  16. AngelesPlumbing

    AngelesPlumbing

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    Not bad for 10 years old
     
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  17. gigz

    gigz

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    Pumps knackered.
     
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