Lennox furnace Alert code 207: Hot surface igniter sensed open
Alert 207 means the hot surface igniter circuit is open. Lennox's guidance is to measure the igniter's resistance and replace it if it falls outside the range in the furnace installation instructions.
Applies to: Lennox communicating gas furnaces on systems using the S30, S40 or comparable communicating thermostats, as documented in the Lennox Residential Communicating Systems Alert Code Guide.
What it means
A hot surface igniter is a ceramic element that glows red hot to light the gas. It fails by cracking, and a cracked igniter is electrically open — which is exactly what this alert reports. What makes Lennox's guidance useful is its specificity: measure the resistance and compare it against the range published in that furnace's own installation instructions. That converts a judgement call into a measurement, and it means the correct range depends on the model rather than being universal. An igniter that reads open is failed by definition; one that reads out of range is failing.
Most common causes
- A cracked or failed hot surface igniter, which is the usual cause.
- The igniter wiring disconnected, loose, or damaged.
- A connector at the igniter not seated.
- An igniter at the end of its service life, since these are consumable parts.
- Damage during previous service work, since igniters are fragile.
How to diagnose it
- Note whether the igniter glows at all during a start attempt, if the furnace has a sight glass. An igniter that never glows fits this alert.
- Note whether the furnace has been serviced recently, since igniters break easily when handled.
- Note the age of the furnace and when the igniter was last replaced, since these are wear parts.
- Do not attempt to measure the igniter yourself — it is inside the burner compartment.
How to fix it
- This is technician work in the burner compartment and ignition circuit.
- Ask the technician to measure resistance against the range in that furnace's installation instructions, as Lennox specifies, rather than replacing on suspicion.
- A replacement igniter should be the correct part for the model, since resistance ranges differ.
- Handle expectations on cost: an igniter is one of the more affordable furnace repairs and one of the more common.
Notes
Hot surface igniters are consumable. They fail eventually on every furnace that uses one, and a furnace more than a decade old that has never had one replaced is due. This alert is often the furnace reaching an ordinary maintenance point rather than developing a fault.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.