How to Replace a Lennox Pulse Ignition Control Unit

Open the Furnace for Repairs

• Shut down the furnace at the thermostat control and wait for the Lennox to cool. Cut off the electricity, which powers the ignition control, at the main circuit breaker box. Once the furnace is cool, remove the service access plate from the side of the unit with a nut driver to take out the bolts.

Remove the Defective Unit

• The ignition control module is on the upper left side of the furnace, above the main control box, on the outside of the heat exchanger. Remove the cover from the control unit. It pulls off with gentle pressure. The ignition control circuit board is underneath. Unplug the wires from the contacts on the control unit and make a note of where they connect so you can reattach each one correctly to the new unit. Taking out the mounting screws on the sides of the control unit releases the part from the furnace for removal.

Install the New Control Unit

• Hold the new ignition control in position and secure it to the furnace with the screws you removed in Section 2. Slide the contact on each wire onto its corresponding post on the new control unit. Snap the cover in place over the new unit.

Close the Lennox and Reactivate

• Secure the service access plate to the side of the Lennox using the bolts you removed in Section 1 and a nut driver to tighten them. Switch on the electricity at the circuit breaker before turning on the Lennox at the thermostat control.