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Lochinvar knight fan speed

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Hvac tech_2
Hvac tech_2 Member Posts: 21
edited December 2017 in THE MAIN WALL
I have a customer with a lochinvar knight that once a year when the temperature drops below zero it trips on fan speed sometime during the knight. Never any visible ice buildup on the concentric vent , it’s the flush style not the cone type. It’s had a new wiring harness. Any thoughts on ramp settings or outdoor reset not allowing it to ramp up enough when the heat is turned down at night. The vent is close to a inside corner but no overhang and it runs fine all year. It is propane fired
Any thoughts
Thank you

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  • DZoro
    DZoro Member Posts: 1,048
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    Two things, concentric vent, and inside corner. Any possible way to standard 2 pipe it and get out of the corner? Sucks to re pipe but,,,,, it's probably going to always be a headache in extreme conditions, and good chance it is inhaling exhaust during the normal season also.
  • Hvac tech_2
    Hvac tech_2 Member Posts: 21
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    Forget to sayIt’s propane fired
  • DZoro
    DZoro Member Posts: 1,048
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    Does the odr read approx. the same as the current outdoor temp?
  • Hvac tech_2
    Hvac tech_2 Member Posts: 21
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    Within a few degree
  • DZoro
    DZoro Member Posts: 1,048
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    Hard to see the inside of the intake pipe on that style of vent. But I'm pretty sure you are getting frost inside the pipe causing the fan to attempt a rpm increase and trip out
  • Tinman
    Tinman Member Posts: 2,808
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    Is there an indirect on this job? If so, are you limiting the fan speed for DHW?
    Steve Minnich
  • Hvac tech_2
    Hvac tech_2 Member Posts: 21
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    Yes there is a squire indirect but not limiting the fan rpm
  • Hvac tech_2
    Hvac tech_2 Member Posts: 21
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    As far as the inside corner, it vents to the side of a brick chimney, so it’s a inside corner for a foot then it’s free
  • DZoro
    DZoro Member Posts: 1,048
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    If intake isn't frosted, can also check for a frozen regulator or insufficient gas line, check incoming pressure during a 100% fire during the cold snap.

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