Baxi 105e what is wrong?

Discussion in 'Plumbers' Talk' started by Rockford, Dec 4, 2017.

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  1. Rockford

    Rockford New Member

    Hi All,
    Please help, had heating but no hot water, sorted this it was the diverted valve. Now all my rads get hot at the top and that’s it. Burner fires up and heats up quick time but then cuts out, I can feel this pocket of hot water race around the system if I follow the pipes but can’t get a bead on what the problem might be. Took it to bits, flushed it, bled it, pressurised it, checked rads for soily bottom, the only thing I’ve not had a look at is the main heat exchanger (thing that sits above the flames). Had the chrome heat exchanger out of the back, flushed it, heating side is a little blacker than the hot water side but water flows through it fine. Had the pump out and plugged it directly into mains, spins fine, plenty of torque, smooth running quiet. There was a blockage in the AAV changed this for a new one???. I’m struggling here please help.

    Regards

    Rockford
     
  2. Mike83

    Mike83 Active Member

    Is it maybe circulating around the built in bypass.
    Is the return pipe below the boiler hot when the flame cuts out?
     
  3. Rockford

    Rockford New Member

    Hi Mike,

    No! the flow pipe gets really quite hot and all the rads flow pipes get hot, the heat then goes up and over the top of all the rads. Once the boiler cuts out the flow pipe cools down relatively quickly, it does take quite a while though before the return pipe to the boiler is noticeably getting any warmer.

    BR

    R
     
  4. Mike83

    Mike83 Active Member

    Sounds like an air or circulation issue.
    I think the bypass. If the bypass is faulty some water goes around the bypass, some around the rads. Once the return pipe heats up inside the boiler the boiler cuts off on the boiler thermostat. The radiators don’t get very hot and the boiler starts to cool. This process just repeats itself.
    Did you replace the complete divertor or strip down and replace parts.
     
  5. Rockford

    Rockford New Member

    Stripped it down and replaced the parts, push rods were quite calcified and I could see that it was stuck
     
  6. Rockford

    Rockford New Member

    The flow pipe gets really hot then the boilers switches off as I would expect it to do because of the temp sensor on the flow pipe from the heat exchanger above the burners, I think I have a flow problem and this is either the diverted still not functioning correctly or I reckon a blockage in the main heat exchanger above the burners. Weekend job I think!
    I’ll keep you posted but thanks for the reply mike

    BR

    Rockford
     
  7. Devil's Advocate

    Devil's Advocate Well-Known Member

    Before you fixed the diverter valve, you did have 'heating'. So that suggest your system is (was) basically working ok - pump etc.

    Now that you've 'fixed' the valve, the opposite is the case - the rads don't heat up properly. It does sound like a reduced circulation issue. Most obvious guess as to the cause in this case - a partially stuck diverter valve :p

    You can get fully refurbished ones for £50.

    Does that boiler have a built-in by-pass? If so, could you check that by placing your hand on it as the boiler fires up for CH?
     
  8. Rockford

    Rockford New Member

    Ha ha indeed yes that is my assumption too! no bypass. I wondered if by cleaning the heat exchanged and fiddling with the diverted valve I make have inadvertently sent some calcification into the main burner heat exchanger and blocked that?
    Big job for me this Saturday but I will post the results
     
  9. Mike83

    Mike83 Active Member

    The bypass connects directly in to the diverter valve.
    It’s a little spring loaded shuttle. It’s made of plastic and brass.
     
  10. Rockford

    Rockford New Member

    Sure you’re not thinking of an HE model? Nothing like that on the 105e, think I’ve seen what you’re referring to on a youtube clip though in my endless pursuit of happiness
     
  11. Mike83

    Mike83 Active Member

  12. Mike83

    Mike83 Active Member

    Had Issues with these parts before. Maybe not on this boiler but worth a thought.
     
  13. Rockford

    Rockford New Member

    Just looking at a 105e manual online
    https://www.tvha.co.uk/wp-content/uploads/2013/10/Baxi-Combi-Instant-80e_105e.pdf
    This is not the same as my 105e and I can see in the schematic on this one it does indeed have a bypass valve, mine does not and the diverter valve is not the same as what is listed in this doc either, mine was installed in about 2004 so might be an older model than in this doc???
     
  14. Rockford

    Rockford New Member

    Just saw your post, that’s the model I have. It has a bypass pipe but no valve
     
  15. Mike83

    Mike83 Active Member

    It will have a valve. It’s not shown on the schematics.
     
  16. Mike83

    Mike83 Active Member

  17. Mike83

    Mike83 Active Member

  18. Mike83

    Mike83 Active Member

    If the main heat exchanger was blocked this would be more evident on hot water than heating.
    I’d be looking at the by pass or diverter valve.
    Obviously the isolation valves are open and all rad valves.
     
  19. Rockford

    Rockford New Member

    Art 82 not shown where does that reside?
     
  20. Rockford

    Rockford New Member

    Yeah all rads are fully open as are the isolator valves
     

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