O9
Buderus
Gas Valve or Gas Supply Fault
O9 error, furnace locked out, burner will not start
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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
Gas valve coil failure, No gas supply or closed gas cock, Faulty wiring to Buderus gas valve, Internal gas valve blockage
How to Fix / Troubleshooting
Safety: Turn off power and gas. Do not attempt to disassemble the gas valve.
Steps:
- Verify gas supply: Confirm the manual gas shutoff valve is open and that other gas appliances are working.
- Inspect wiring: Check the gas valve connector and wires for damage or loose terminals. Reseat the plug on the valve and control board.
- Listen for valve click: With power restored and a call for heat, listen for a distinct click from the gas valve. No click may indicate a failed coil or no control signal.
Gas valve testing and replacement must be performed by a licensed gas technician with proper leak testing and combustion verification.
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Repair Difficulty
Professional Required
5/5
Required Part
Buderus Gas Valve Assembly
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