E21
Remeha
Safety interlock open (e.g., door switch, flue inspection switch)
Display shows E21, furnace will not start, often after service work
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Combustion chamber door not correctly closed, Flue inspection cover open, Faulty door interlock switch, Disconnected safety loop wiring
How to Fix / Troubleshooting
Safety first: Do not bypass safety interlocks. They ensure safe operation of the furnace.
- Check covers: Ensure all service covers, especially the combustion chamber door and flue inspection hatches, are properly closed and latched.
- Inspect interlock switch: Locate the door or cover switch and verify that it is actuated when the cover is closed. Adjust the cover or switch position if necessary.
- Check wiring loop: Follow the safety loop wiring between switches and the PCB. Ensure all connectors are secure.
- Continuity test: With power off, a technician can test continuity through the safety loop to identify an open switch or broken wire.
- Replace faulty switch: If a switch does not close reliably, replace it with the correct Remeha part.
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Repair Difficulty
Medium
3/5
Required Part
Door Interlock Switch
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