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Harman pb 105 overheat zone issue.

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Tdiguy, Feb 20, 2013.

  1. Tdiguy

    Tdiguy Member

    Joined:
    Feb 20, 2013
    Messages:
    28
    I have a harman pb 105 that i have had for a few years now. Getting it installed and working was a pain. The local dealer near me does not really install these per say. They simply pipe them and by that only the intake and exhaust. So I had the dealer drop it off. I had a master plumber come to do the install and he was nice enough to connect it to power and plumb it up and such. I recently noticed that the overheat zone had never been connected. Course i noticed this because i just switched to a different brand of pellets that seem to burn hotter because several times now my boiler has stopped working and been flashing overheat.
    So i looked into it a little bit and i found a relay in box product which is a self contained dpdt relay so i figured i could have the boiler trigger that to fire up the circulator pump and open a zone.
    I got it all wired up but now the overheat zone is always on. Mind you the led itself isnt always on but the circuit is always on. The wiring i dont think could be easier really. 2 wires for the coil and then the switched wires. When i disconnect the blue wire from harman of course the relay shuts off but when i connect it it goes right back on. I am having a hard time thinking that its anything other than a bad logic board since there is so little that could be wrong. I am also not sure if i call the dealer if i will get any help with it at all since they wouldn't connect it to power to start with.

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  2. PassionForFire&Water

    PassionForFire&Water Minister of Fire

    Joined:
    Jan 14, 2011
    Messages:
    595
    Loc:
    Billerica, MA
    I guess there is the overheat temperature sensor that is set at a to low temperature.
    Increase that set point to 185F or 190F.
    If it has a differential setting, set that at 5F
    If all this is not possible, I would just install a strap on overheat aquastat to control the overheat circulator/zone valve
  3. Tdiguy

    Tdiguy Member

    Joined:
    Feb 20, 2013
    Messages:
    28
    The overheat temp for this boiler is hard set in the logic board i have no way to change it. Also even when the overheat light is off there is power to the overheat zone which i think it the real problem.
    Any idea what a new logic board costs? I am having a heck of a time finding the pricing. If they are over 90$ i will probably go with a different solution like an aquastat. I figure i can still use my dpdt relay with the aquastat and have it cut power to the boiler (while its too hot that is) turn on the circulator and open a zone valve. Maybe cutting power to the boiler is unneeded but whats a little overkill here and there when it comes to recovering from a condition that brings equipment close to design limits.
  4. Tdiguy

    Tdiguy Member

    Joined:
    Feb 20, 2013
    Messages:
    28

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