Lennox error codes, explained
Lennox gas furnaces (SureLight and current EL/SL series). Codes below: E-codes (E200–E271) and Watchguard. Each guide covers what the code means, what you can safely try yourself, when to stop and call a technician, and what the repair typically costs.
Lennox 'Watchguard' — Soft lockout (auto-retry pending)
Watchguard is Lennox's soft-lockout state. The flame-failure variant means five ignition attempts failed to prove flame; the control waits 60 minutes and automatically retries (the pressure-switch variant waits only 5 minutes). A power cycle clears it immediately — but clearing the lockout doesn't fix the cause, and the classic cause is a dirty flame sensor.
Lennox E200 — Rollout circuit open (hard lockout)
The flame rollout switch tripped or its circuit is open — flames escaped the burner enclosure at some point. This is a hard lockout and a combustion safety event: Lennox's service literature says correct the cause or replace the switch, and the cause is what matters (blocked heat exchanger, venting failure, burner problems).
Lennox E201 — Indoor blower communication failure
The control board lost communication with the blower motor — power loss to the motor or loose wiring between board and blower. No airflow means no safe heat, so the furnace stops.
Lennox E223 & E227 — Low pressure switch open
Both codes point at the low-fire draft pressure switch failing to prove: E223 = failed open (never closed), E227 = opened during ignition or run. Causes: blocked vent or combustion-air intake, a struggling inducer, or — very common on 90%+ condensing units in winter — frozen or clogged condensate. (Sibling code E224 is the switch stuck CLOSED.)
Lennox E250 — Limit switch circuit open
The high-temperature limit opened — the furnace overheated, and if the limit doesn't reclose within 3 minutes the control takes a 1-hour soft lockout. Same story as every brand's limit code: it's almost always airflow (dirty filter, blocked returns, dirty coil or blower).
Lennox E270 & E271 — Soft lockout, ignition retries exceeded
The E-code versions of Watchguard: E270 = maximum ignition retries with no flame current sensed (dirty flame sensor territory), E271 = retries exhausted with the last failure caused by the pressure switch opening (venting/inducer territory). Both are soft lockouts that auto-retry.