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high efficiency Utica UB90-150 won't start

sureshkachsureshkach Posts: 7Member
The green light is on on the IBC board and the circulator starts. We have replaced the pressure switches but nothing happens. Blower or indicator lights do not come on to indicate what could be wrong.


  • DZoroDZoro Posts: 902Member
    Does the inducer start?
    Is venting free and clear of debris?
    Condensate trap and drain piping clear?
    Any blinking lights?
    What light/s are on?
  • sureshkachsureshkach Posts: 7Member
    Removed the blower assembly and flushed the heat exchanger to remove all aluminum oxide. Put it back together but no change. Green power light is only light that is on. No blinking lights. Circulator is on calling for heat but nothing else happens. Blower does not come on. This was yesterday.

    This morning put boiler on, circulator started, blower came on, purge light came on, it ignited for about 10 to 15 seconds. Then it switched off and only green light is on on IBC. Thank you for any help.
  • DZoroDZoro Posts: 902Member
    Clean all the molex connectors. Confirm all good wiring connections. Confirm call for heat connections.
  • IronmanIronman Posts: 5,233Member
    How about telling everything you've done to the boiler?

    Why did you replace the pressure switches and did you use the exact replacement?

    If memory serves me, that boiler has a LWCO like the modulating 200m. What's your static fill pressure? Did you purge the air from the block? Did you clean the LWCO probe?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • sureshkachsureshkach Posts: 7Member
    Thanks so much for suggestions. Trying them all.

    LWCO is RB-122-E with self cleaning probe
    The psi pressure is 20
    Just purged and has no air
    Pressure switches are Utica original parts with same exact part number. The reason I changed the switches is because the board only had a green light.
    After doing what you suggested the boiler is now coming on for 3 minutes, then goes off and only the green light on the IBC board is on and the circulator is calling for heat.
    I have to switch boiler off for 6 to 8 hours before it will try to start again.
  • IronmanIronman Posts: 5,233Member
    edited October 19
    It sounds like your condensate trap or line is not clear. The pressure switch won't make if it's blocked. You need to check all the way from where the vent pipe connects to the block, out to where it drains.

    Remove the plug and clear the Tee and remove the flexible coupling that connects the flue pipe to the block and clear the bottom of the block.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • sureshkachsureshkach Posts: 7Member
    After the suggestion to clean the system out and check the PSI pressure, the system ran for four days then stopped again. Same thing again, green light is on, circulator is on but system will not come on. Any other thoughts? Thank you.
  • IronmanIronman Posts: 5,233Member
    Do it again. When you originally flushed the block, you loosened a lot of material and it's settling in the bottom of the block and Tee.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • sureshkachsureshkach Posts: 7Member
    Mr Ironman I have done everything you have said.
    I flushed the system twice, taken the T off and cleaned it. I have cleaned the condensate pump and fittings. The PSI pressure is between 18 and 20. System came on for 3.5 minutes as before and went off again with just the green light on. Circulator is on but system will not come on again u less it is switched off for hours. Then only for a few minutes. Frustrated and at a loss as what I can do now. Any new thoughts?
  • sureshkachsureshkach Posts: 7Member
    after leaving it overnight the system has no change.
    green light is on -circulator is calling for heat-it tried to come on blower came on for 5-10 sec and that was it
  • DZoroDZoro Posts: 902Member
    How does the inducer sound when it does come on? Are you capable of testing power to the inducer? If you have cleaned all the molex connections. Sounding like you are probably in need of a new board.
  • sureshkachsureshkach Posts: 7Member
    when it comes on its 110 and it sounds fine
    how do you clean molex connections .the board was changed
  • IronmanIronman Posts: 5,233Member
    edited October 23
    You may have a bad aquastat. What temp is it set at?

    There are proper ways to diagnose controls and issues like this, but it requires proper instruments and training of knowing how while onsite. Short of that, it's a guessing game and unscientific.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • DZoroDZoro Posts: 902Member
    Turn the power off. Inside each molex connection there is either a male or female connector. Usually use a thermostat wire for the females, and a knife blade or small screwdriver for the males. At the same time doing all this tug on the wiring to confirm a good solid connection with the connector. Small steel brush can also be helpful.
  • JUGHNEJUGHNE Posts: 6,072Member
    I chased my tail on my own Lochinvar KBN 080.
    It would intermittently fail and lock out on low fan speed.
    Book says that if air in/out pipes are clear to replace fan and then board.
    I have new board and fan in the box yet.

    It turned out that one zone valve end switch was not giving good contact. That in turn activates 2 more relays. The intermittent operation would lock out the board. The other zones would keep the boiler relay on if calling.

    This is just to show how new parts get installed and one still has a problem.....try another part :( .
    If you just find the terminals that force the boiler to run and jumper them. This eliminates most of the Tstat/control wiring and maybe it is something simple.
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