F28
Protherm
Ignition Lockout – No Flame
F28 displayed, repeated ignition attempts with no flame, then lockout
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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
No gas supply to Protherm furnace, Closed manual gas cock, Air in gas line after service, Faulty ignition electrode or transformer, Defective gas valve not opening
How to Fix / Troubleshooting
Safety first: Turn off power and gas. Do not repeatedly reset a furnace that will not ignite; unburned gas can accumulate.
- Step 1 – Check gas supply: Confirm other gas appliances work. Ensure the furnace gas cock is fully open.
- Step 2 – Purge air (technician): After gas work, a technician may need to purge air from the line safely.
- Step 3 – Inspect ignition system: Check the ignition electrode and cable for damage and correct positioning. Clean or replace as needed.
- Step 4 – Gas valve and PCB tests: A technician should verify that the gas valve receives power during ignition and that gas pressure is correct. Replace the gas valve or PCB if defective.
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Repair Difficulty
Professional Required
5/5
Required Part
Gas Valve Assembly
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