Lennox furnace repair is the Lennox request we hear most in Sunnyvale, Santa Clara and Cupertino, followed by air conditioners and heat pumps once summer heat arrives. The equipment is built by Lennox International, and the lines we find in local homes are central air conditioners, heat pumps, gas furnaces, air handlers, ductless units and indoor air quality add-ons. Whatever the model, the work is the same discipline: confirm the symptom, read the rating plate, and test the step that fails.
Lennox furnace won’t heat: the sequence we follow
A modern gas furnace lights in a fixed order, and the control board will not move on until the previous step checks out. That makes the failure point findable:
- Thermostat call. The thermostat closes the heat circuit. No call, no furnace, so we confirm the signal arrives at the board.
- Inducer motor. A small fan purges the heat exchanger and flue before ignition.
- Pressure switch. It proves the inducer is moving air. A blocked flue, a cracked hose or a weak inducer stops the sequence here.
- Ignition. A hot surface igniter glows, or on some models a spark igniter fires. Cracked igniters are a frequent winter failure.
- Gas valve and flame sensor. The valve opens and the sensor must prove the burners lit within seconds. A dirty sensor makes a furnace light, then shut off, over and over.
- Blower. After a short delay the blower sends warm air through the ducts. If poor airflow overheats the heat exchanger, the high-limit switch shuts the burners down while the blower keeps running.
The control board usually blinks an LED code that names the failed step. A photo of that light through the panel window is useful before you call. More detail is on our furnace repair page.
Common Lennox symptoms
| What you notice | Likely cause | What it usually takes |
|---|---|---|
| Furnace clicks, inducer runs, no flame | Igniter or pressure switch | Testing both, replacing the failed one |
| Burners light, then go out | Dirty or failing flame sensor, gas pressure | Cleaning or replacing the sensor, checking pressure |
| Warm air for a few minutes, then cool | High-limit trip from a clogged filter or closed vents | Filter, return and duct check |
| AC runs, house stays warm | Weak capacitor, outdoor fan, dirty coil or low charge | Electrical and airflow tests before gauges |
| Outdoor unit hums, fan won’t spin | Failed capacitor or fan motor | Testing under load, then the part |
| Water at the furnace in summer | Blocked condensate drain from the AC coil | Clearing and testing the drain |
Lennox air conditioners and heat pumps
When a hot spell pushes afternoons past the 90s, a Lennox AC that was marginal in May falls behind. We check thermostat demand, filter restriction, the outdoor fan, capacitor and contactor readings, and coil condition before looking for refrigerant or compressor trouble. On heat pumps we add the defrost cycle and the reversing valve, since one outdoor unit does both jobs. See AC repair and heat pump repair.
Air handlers and indoor air quality
Homes with a Lennox heat pump usually have an air handler indoors instead of a furnace, sometimes with electric heat strips for backup. The blower, the indoor coil and the drain pan all live in that cabinet, so a musty smell, water on the floor or weak airflow often starts there. Lennox also makes air cleaners and filtration that mount at the air handler or furnace. When wildfire smoke drifts in during late summer or fall, that filter carries most of the load; see indoor air quality and air purifier installation.
Repair or replace an older Lennox
One failed igniter or capacitor on a furnace that otherwise runs well is a repair. The picture changes when the same system has needed several major repairs, when the heat exchanger shows cracks or rust-through, or when parts for an older model are hard to find. We put the repair history, age and parts situation side by side. If replacement makes more sense, the quote should list the furnace or condenser, installation labor and the permit separately, with any upgrades shown as options; see furnace installation.
Lennox warranty paperwork
HVAC Sunnyvale works on Lennox equipment as an independent contractor, with no ties to the manufacturer. Parts coverage depends on the model, the install date and whether the equipment was registered, and claims go through Lennox’s own process. Keep the model and serial numbers from both the indoor equipment and the outdoor unit handy. Repairs we make are backed by our warranty covering both parts and labor, and yearly maintenance can catch a worn igniter or a dirty flame sensor before it fails on a cold night.