A20
Wolf
Safety Circuit Open (Limit Switch / Safety Chain Fault)
Boiler displays A20, burner does not start, safety chain open
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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
Open safety temperature limiter, Flue gas safety thermostat tripped, Loose wiring in safety loop, Faulty safety thermostat
How to Fix / Troubleshooting
Safety: Do not bypass any safety devices. Identify and correct the cause of the trip.
- Allow boiler to cool: If a safety thermostat has tripped due to overheating, wait until the boiler is cool.
- Manual reset (if provided): Some safety thermostats have a manual reset button accessible to a technician. Do not press it repeatedly without finding the cause.
- Check for blocked flue or poor circulation: Overheating may be due to system or flue issues; see related faults (A03, A05, A13).
- Technician inspection: A professional should test each safety device in the chain and replace any faulty thermostat or wiring.
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Repair Difficulty
Hard
4/5
Required Part
Safety Thermostat / Limit Switch
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