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 sensed
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.
What the fix costs
The resistance measurement Lennox prescribes is a price fork: an ignitor reading open or out of its published range is a $150–350 installed repair ($20–60 for a universal silicon nitride element, $40–120 OEM), while an ignitor that measures healthy shifts suspicion to the triggering circuitry on the control and the job toward a board at $400–900. One parts note from the ignitor guide worth applying at replacement time: specify silicon nitride rather than the older spiral-carbide style — it is the same money installed and lasts years longer, which matters on a code that will return if the element is the weak point. The one-hour soft lockout means the furnace retries on its own schedule; an E290 recurring across multiple lockout cycles has had its coin-flip answered and deserves the measurement, not another element on spec.
DIY or call a pro
The word “circuit” in this code is what changes the DIY calculus relative to a plain failed-ignitor situation. Lennox names two suspects — the element and the circuitry that fires it — and only one of them is the part a homeowner can buy; the other is the control board, and telling them apart requires the resistance check against the model's published specification, made with the circuit isolated inside the burner compartment. Swapping the element without that check is a guess that costs the price of the part when wrong and, worse, delays the real repair through another season of hourly lockouts. Homeowner contributions that hold value: the age of the current ignitor if it has ever been replaced (a nearly new element behind an E290 points hard at the triggering side), and whether ignition attempts show any glow. Leave the measurement, and everything past the burner door, to the visit.
The same fault on other brands
The part-versus-circuit ambiguity E290 names is handled differently across families: Trane's 9 flashes merges a failed igniter with a bad ground into one code its control cannot split, while the legacy Goodman/York table isolates the board side outright as 12 red flashes, ignitor relay failure. The igniter codes hub sorts which brands can tell the element from its driver — Lennox's E290 names both suspects in one code and hands the tiebreak to the resistance spec.
What this looks like
From the outside, this usually shows up as the furnace turns over but never lights — that walkthrough covers what to check in order, and when it stops being a homeowner job.