Just completed replacing the control board and sail switch in my Suburban NT 20 SQ furnace. It now cranks out the heat....quickly. It is a 20k btu with two ducts and it recently started having intermittent heat. When it did light the flame looked clean and blue, although small, through the observation window but it would take a long time to reach the selected temp on the thermostat. It then started timing out and not lighting and progressively worsened. I measured the ambient temperture last week at the vent when it was lit and it measured 105 F. Today after replacing the control board and sail switch, for good measure since I had it apart, the ambient temperture measured at the vent is approx 150 F. So my question is has anyone else measured their heater temp output directly at the vent? Another test I performed was seeing how long the heater would run to raise the temp 12 degrees. The answer is 4 min. Temp outside during the test is 45 F.
So how hot is too hot?
So how hot is too hot?
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