Display shows Er9 and furnace stops; blowers may continue for cool-down.

Safety first: Turn off and unplug the furnace. Allow all components, especially the flue and exhaust housing, to cool. Do not operate the unit until the cause of overheating is found.

Steps:

• 1. Inspect venting: Remove the vent cap and check for obstructions. Clean the vent pipe thoroughly, including elbows and tees, to remove ash and creosote.
• 2. Check combustion blower operation: When the unit is running, the combustion blower should start promptly and run at full speed. If it is noisy, slow, or not starting, test and replace the blower as needed.
• 3. Verify feed rate settings: Ensure the heat level or feed rate is set according to the manual and not excessively high for the venting configuration.
• 4. Locate the exhaust high limit sensor: Often a snap disc or temperature probe mounted on the exhaust housing or flue outlet. Inspect for loose wiring or signs of overheating.
• 5. Test/replace the sensor: With power off and the unit cool, test the sensor or snap disc for proper operation per the manual. Replace with the correct US Stove exhaust high limit if it is out of specification.
• 6. Restart cautiously: After cleaning and repairs, restart the furnace on a lower heat setting and monitor flue temperature and operation. If Er9 recurs, contact a qualified technician to evaluate installation, draft, and control board operation.