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Buderus gb142 code 6a

vipertecvipertec Posts: 6Member
I have an issue with a gb142 setting 6a fault. Had a broken Venturi which I replaced. Gas pressures all checked within specs Cleaned as good as I could but manual states to spray exchanger with mineral oil then high fire. Well. The issue is it doesnt fire so this won’t work. If I block air intake tube it fires for about 15 seconds then goes out. Buderus says it’s dirty but from what I compared to this unit seems rarely clean. Any help?

Comments

  • Big Ed_4Big Ed_4 Posts: 1,094Member
    edited March 11
    What was the gas pressure measured before the unit at rest and as the unit tries to fire ? Does the fan run ? Does the igniter glow ? It only fires when blocking the air intake ? Could be a Dirty heat exchanger or blocked vent . Check the PVC vent ? Birds nest ? .Is there heavy deposits of white crud blocking the passages between the disks and tubes along the heat exchanger ? Wash it down with just plain water through a sprayer to open up the passage. Dont forget to open the bottom access for inspection of the lower heat exchanger ...scrub with a wet stiff paint brush. Clean the rod with fine steel wool , stay away from the igniter though out the washing .. Does it fire up ? Now use the mineral oil .Use the paint brush... May take a few tries and cycles to clean ... At the end replace the igniter and rod ...
    I have enough experience to know , that I dont know it all
  • vipertecvipertec Posts: 6Member
    I don’t remember gas pressures but when it was checked last Bosch tech stated we were within range we originally had good size crud buildup but with scrubbing and spraying it looks much cleaner. We checked the vent tube and it is not blocked. We turn it on (if we block air inlet)igniter glows,gas valve opens,it lights then slowly flame diminishes and then valve shuts,if air tube isn’t blocked it won’t even light. . We borescoped rear of unit,looks clear,removed top and bottom covers,trap bottle. No blockage. Originally Venturi was broken so that was replaced but still 6a??some people say could be fan but Bosch people say it is dirty??
  • vipertecvipertec Posts: 6Member
    Forgot to mention the fan does operate
  • HVACNUTHVACNUT Posts: 1,582Member
    Bosch never mentioned a throttle adjustment on the gas valve?
  • vipertecvipertec Posts: 6Member
    Also gas pressures were somewhere in the 11-12 range from what I remembered. They even tried to up the regulator pressure abit but no good
  • vipertecvipertec Posts: 6Member
    No they didn’t. They just keep saying to clean it. We have done that numerous times. As for what I have seen of images online of a cleaned exchanger this one looks better than most of them. I will say it was very dirty wth good size clumps but with bore scope I can see it is all clear
  • IronmanIronman Posts: 4,576Member
    "Venturi was replaced"? Did you make sure that you had the right size one and also replaced the gasket?

    It sounds like you're getting too much air and either of those could cause that.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • Big Ed_4Big Ed_4 Posts: 1,094Member
    It now lights on its own ... then fizzles out... You clean the rod with fine OO steel wool ... To note the igniter plays a part on letting the control know thats it's lit ... There is a meter reading to check .. Good habit to just replace... They wear out.... Either in the flame signal or gas flow ... Bring in the right meters and combustion analyzer then call Buderus , Ask or Noel on the phone , Then it was Charley ... Field rep , not sure if still out there... Maybe not , get Noel on the phone
    I have enough experience to know , that I dont know it all
  • vipertecvipertec Posts: 6Member
    We replAced Venturi with correct part and new oring. It doesn’t light on its own. It will only ignite if air inlet is covered by hand,I was told that the rod was not the cause as when you block the inlet and it fires that the flame indicator is on then does go off ,when gas valve shuts,showing what is taking place. They state that the flame needs to take place before the the rod can sense its on.is it possible that the fan (which sounds fine) could be running incorrect speeds and causing it to not fire?
  • IronmanIronman Posts: 4,576Member
    edited March 13
    A major part of learning how to diagnose technical problems is to realize that it takes more than technical knowledge. Look at the entire picture. Did the boiler fire and run before you cleaned it and changed the venturi? If so, then something you've done has caused it not to run now.

    Are you sure you have the CORRECT venturi and the gasket properly seated? I've seen your exact scenario from both of those things being wrong.

    Also, are you sure you re-assembled the burner plates correctly?

    Do you have the service manual for it?
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • IfollowinstructionsIfollowinstructions Posts: 23Member
    All the big companies have us thinking form there advertising that the heat exchangers rarely get clogged, this has been been the first year that we've came across clogged heat exchangers, especially on European boilers. You need to set up a pumping station & flush the heat exchanger with boiler cleaning agent, this can take a few hours and very tedious. Typically the tech support have us change the gas valve, Venturi, ignitor. fan then after a thousand dollars of stock being spent & the parameters settings can't be met- they tell us to flush the heat exchanger....
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