Lennox 'Watchguard' — Soft lockout (auto-retry pending)

What this error means

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.

Symptoms

• Furnace stopped heating; display/LED shows a Watchguard state
• Heat mysteriously comes back about an hour later, then fails again
• Recurs every day or two

Try this first (safe DIY steps)

1. Power off at the furnace switch ~30 seconds and restore — Lennox's own service literature gives power interruption as the reset
2. If it recurs: clean the flame sensor (our universal guide — 20 minutes, ~$0)
3. Check filter and venting while you're at it

Safety: power off before any physical intervention. Never bypass covers or interlocks — fuser areas run hot enough to burn.

When to call a technician

Recurring Watchguard after a sensor cleaning = pressure switch, venting, or gas-side diagnosis ($150–$400 typical).