Lennox manufactures several models of furnace that work with the company's Merit Series thermostats. Like all appliances, these furnaces experience difficulties from time to time, up to and including complete failure to function. Some of these problems are easily treatable, while others leave a homeowner no choice but to contact a repair professional.
On Lennox furnaces with Merit Series thermostats, the thermostat is wired directly to the furnace but still sits above or beside the main unit. If the thermostat is not causing the unit to respond, the problem may stem from a disconnect between the unit and the thermostat. Check that the thermostat is powered on and that the wiring runs all the way from the thermostat to the furnace control board. Next, ensure that the wiring connects at the proper leads. Wiring that is properly connected but unresponsive may suffer from burnout. Replace the wiring between the devices and check to ensure proper operation.
If the thermostat is wholly unresponsive, the independent battery may require replacement. The Merit Series thermostat is a digital controlling system that operates on electrical power provided by a disc-shaped battery. Replacing the thermostat battery should restore at least display functionality to the thermostat.
If the display is responsive but the furnace is not, the problem may stem from a broken starter. Lennox furnaces that operate with a Merit Series thermostat feature an electrical starter. This starter provides the initial spark that ignites the fuel in the furnace. Without this spark, fuel is simply expelled into the air, creating a possibly toxic situation. Turn off the fuel for the furnace immediately if a broken starter is the suspected issue. Contact a certified repair technician for repair or replacement options.
A working starter does very little if no fuel is supplied to the furnace. Ensure that the fuel valve is set to the fully activated position and that fuel is coming out of the fuel line. You can usually hear a whispering sound when the fuel is activated. If no sound is coming out, contact your fuel provider for service.
Lennox Merit Series furnaces are equipped with automatic shut-off switches that engage when the furnace is about to overheat. This happens often when the vents, which help dispel excess heat and debris, are clogged or blocked. In this instance, removing the vent clog restores service to the unit.