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Troubleshooting a High Efficiency Condensing Furnace


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No Ignition - Clogged Flue Vent
Troubleshooting a High Efficiency Condensing Furnace

Vent pipes are large diameter and bring fresh outside air to the sealed combustion chamber and vent low temperature exhaust flue gasses to the outside.

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In addition to the possible clogged condensate line problem tripping the pressure switch as discussed in the previous step, the pressure switch can also be tripped by an obstructed exhaust flue gas vent pipe.
  • Similar to an obstructed air intake pipe, check for obstructions such as nests or leaves but also check for inadequate sloping of the vent pipe (minimum upward slope from furnace of ¼” per foot) and make sure the exhaust pipe is supported every 5 feet of horizontal run.
  • A sagging or improperly sloping exhaust vent pipe can collect condensate water and restrict flow resulting in a tripped pressure switch.

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