A gas furnace converted to LPG struggles to fire correctly and is sooting up. What is the most likely cause?

In the scenario where a gas furnace converted to LPG is struggling to fire correctly and is experiencing sooting, the most likely cause is low LPG pressure. When the pressure of the LPG is insufficient, it can lead to incomplete combustion. This incomplete combustion results in excess fuel not burning properly, which subsequently creates soot.

LPG systems require specific pressure levels to operate efficiently and effectively. If the LPG is not at the correct pressure, it does not atomize properly during combustion, leading to a rich fuel mixture that cannot ignite fully. This results in the accumulation of soot in the furnace, indicating improper operation.

Other potential issues, such as incorrect thermostat position and short burner cycles, could affect the overall performance of the furnace, but they would not specifically cause sooting in the way that low LPG pressure would. High pressure in the gas line could lead to different problems, including flooding the burner with too much gas rather than insufficient pressure that causes sooting. Therefore, addressing the low LPG pressure is crucial for restoring the furnace to its proper firing and combustion efficiency.