Boiler Intermittently not firing up on call for Heat

Discussion in 'HVAC Heating & Cooling' started by ClFrank13, Jan 30, 2021.

  1. ClFrank13

    ClFrank13 New Member

    Joined:
    Jan 30, 2021
    Location:
    Long Island
    I have a Slantfin Sentinel SE 140 (gas boiler) with a Honeywell L8148E 1273 aquastat that I had no issues with sine installed 15 year ago.

    My system has 2 zones, in one of my heating zones when there is a call for heat it intermittently fails to fire up the boiler - if that zone does fail, the zone valve opens but the boiler wont fire up unless I do a power cycle to the boiler or lower the temperature on the thermostat below the set point and then raise it back up. This only happens in that one zone - the two zones share the same circulator pump and the circulator pump won't kick on either if that zone fails (unless the other zone id cal;ling for heat).

    After doing some research, I understand this specific aquastat is very flaky - and figured I start by replacing that but since it only happens in the one zone intermittently, I am curious if anyone has suggestions on what else to look for. I verified it s not the thermostat because I switched the stats to the two zones and the problem stays with the same zone.

    Thanks in advance

    Cliff
     
  2. fitter30

    fitter30 Well-Known Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Honeywell aquastat looks like it has a open relay. If the relay is pulled in should make boiler contacts to start boiler. Having to turn thermostat down and then back up boiler seems to have a signal but has failed to lite and locked itself out. Does your your boiler have a ignition module? Take a pic of the wiring diagram and module if it has one.
     
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  4. ClFrank13

    ClFrank13 New Member

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    Jan 30, 2021
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    Long Island
    Thanks for the response. It has a standing pilot - no ignition module.
     
  5. fitter30

    fitter30 Well-Known Member

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    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Standing pilot or spark ignition?
     
  6. ClFrank13

    ClFrank13 New Member

    Joined:
    Jan 30, 2021
    Location:
    Long Island
    Standing Pilot
     
  7. fitter30

    fitter30 Well-Known Member

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    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Screenshot_2021-01-30-15-07-39.png Flue damper open thermostat is calling check roll out and vent switches. Meter gas valve th terminal check both safeties for 24 volts
     
  8. ClFrank13

    ClFrank13 New Member

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    Jan 30, 2021
    Location:
    Long Island
    Just failed again, if I tap on the zone valve it fires up - I assume its a bad connection to the end switch
     
  9. fitter30

    fitter30 Well-Known Member

    Joined:
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    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    If you don't want to replace zone valve just wire in a relay powered by valve.
     
  10. ClFrank13

    ClFrank13 New Member

    Joined:
    Jan 30, 2021
    Location:
    Long Island
    Thanks for all your responses... it must have been a faulty connection of the zone valve wasn't triggering the end switch - after removing and re-tightening all the wire nuts last week, its been working fine... Thanks again!
     
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