Lennox Furnace Error Code E347

E347 means the integrated control board is not producing a 24-volt output on its Y1 terminal when paired with a non-communicating outdoor cooling unit. The board detected that the Y1 Stage 1 relay failed to switch the signal through to the outdoor unit. This prevents the air conditioning system from starting. The fault can be caused by a failed relay on the board itself, a wiring short, or poor terminal connections.

Some causes, such as loose terminal connections or visible wiring damage, can be identified and corrected by a knowledgeable DIYer comfortable working with low-voltage wiring. However, if the Y1 relay on the integrated control board has failed, the board typically must be replaced as a unit, which involves handling line-voltage components and should be done by a qualified HVAC technician. Always shut off power to the furnace before inspecting any wiring.

Repair costs vary depending on the root cause. If the fix involves tightening connections or correcting a wiring issue, you may only pay a diagnostic service call fee, typically in the range of $75 to $150. If the integrated control board needs to be replaced, total parts and labor costs generally range from $400 to $900 or more depending on the specific board and local labor rates.

A reset can clear E347 if the fault is intermittent and the control board subsequently senses the Y1 input signal correctly after restart. However, if the Y1 relay has permanently failed or if a wiring problem persists, the code will return immediately or on the next cooling call. A fault that clears on reset but comes back consistently points to a hardware problem that requires further diagnosis.

E347 is not a combustion safety fault. It relates to the cooling control circuit and will prevent your air conditioning from operating, but it does not create a fire or carbon monoxide risk. Your furnace heating function should continue to operate normally. That said, leaving wiring shorts unresolved can cause further board damage over time, so the issue should be addressed promptly.