Lennox furnace E290: Ignitor circuit fault — failed ignitor or triggering circuit
E290 reports a fault in the ignitor circuit — either a failed hot surface ignitor or the circuitry that triggers it. It carries a one-hour soft lockout.
Applies to: Lennox gas furnaces with a seven-segment diagnostic display on the control board, such as the ML193UHEK, per installation instructions 508565-01.
What it means
The control energises the hot surface ignitor and watches the current it draws. E290 says what it measured does not match a working circuit. Lennox names both possibilities in the code itself: a failed ignitor, or failed triggering circuitry on the control. Their instruction is to measure the resistance of the hot surface ignitor and replace it if it reads open or falls outside specification — which means the specification lives in the documentation for that particular furnace, not in a universal number. An ignitor that reads open is failed by definition. One that reads out of range is on its way. The lockout is soft and one hour long, and Lennox notes it clears when flame has been proven stable, so a furnace with a marginal ignitor can appear to recover on its own.
Most common causes
- A cracked or failed hot surface ignitor, which fails open. These are brittle and consumable.
- Ignitor wiring damaged, loose, or unseated at the connector.
- Failed triggering circuitry on the control board.
- An ignitor intact but outside its specified resistance range.
- Damage from previous service work, since skin oils and handling break these.
How to diagnose it
- Note whether the ignitor glows at all during a start attempt, if the furnace has a sight glass.
- Note the age of the furnace and whether the ignitor has ever been replaced — these are wear parts, not defects.
- Note whether the fault started immediately after a service visit.
- Do not measure the ignitor yourself. It sits in the burner compartment.
How to fix it
- Technician work in the burner compartment.
- Ask that the ignitor resistance be measured against the specification for this furnace rather than replaced on suspicion.
- A replacement must be the correct part for the model, since resistance ranges differ.
- If the ignitor measures in range, the fault is in the wiring or the control's triggering circuit, and swapping the ignitor will not fix it.
Notes
The communicating alert list uses 290 for the same thing, one of several numbers that agree between Lennox's two systems. That agreement is exactly why the ones that disagree are easy to miss.
Related
- Alert code 290 — Ignition circuit fault — Watchguard
- E270 — Soft lockout — retries exceeded, no flame current
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.