How to Fix / Troubleshooting

Safety: Turn off power before accessing the control board or limit switches.

Steps:

Locate all limit devices: Identify the main high limit on the heat exchanger panel and any rollout switches near the burners. Check for manual reset buttons on rollout switches.
Check continuity: With power off, use a multimeter to check continuity across each limit. Any open device (no continuity) must be investigated. Manual-reset rollout switches that are tripped should only be reset after determining the cause.
Inspect wiring: Follow the limit circuit wiring from the control board through each limit device. Tighten loose spade connectors and repair damaged wires.
Address overheating causes: Replace dirty filters, open closed registers, and verify blower operation.

Note: If all limits are closed and wiring is intact but the board still shows a limit lockout, the control board may be defective.

Furnace does not respond to thermostat; status LED shows 11 flashes repeating.

Possible Causes