Error F28 on Vaillant Boilers: Causes, Reset, and Repair Guide
When a Vaillant boiler displays fault code F.28 (or F28), it signifies that the appliance has made three unsuccessful attempts to establish a combustion flame during startup. Both heating and domestic hot water are instantly disabled. Follow these diagnostic steps to identify the root cause.
Initial Checks Before Calling a Technician
1. Ensure the yellow gas lever under the boiler is fully open.
2. Check if your smart gas meter is locked out (if prepayment or external safety valve tripped).
3. In freezing sub-zero weather, inspect the plastic outdoor condensate drain pipe: if ice has frozen inside the discharge tube, water backs up and triggers F28.
How to Reset Error F28 on Vaillant Boilers
Press and hold the button marked with a crossed-out flame or flame icon for 3 seconds. The boiler will purge the combustion chamber and attempt ignition.
Note: Do not press the reset button more than three times consecutively; if ignition fails repeatedly, allow an authorized technician to inspect the gas valve.
Technical Faults Behind Persistent F28 Errors
1. Faulty Gas Valve Solenoid: Fails to modulate gas supply during the ignition ramp.
2. Worn Ignition / Sensing Electrode Assembly: Weak electrical spark or degraded ceramic insulator.
3. Defective Electronic Main PCB: Failure in the flame rectification amplifier circuit on the motherboard.
FAQ
Why does error F28 only appear during freezing winter mornings?
Because the external condensate drain pipe freezes solid in sub-zero temperatures. Thawing the exterior plastic pipe with warm water often resolves the fault immediately.
How much does a Vaillant gas valve replacement cost?
An authentic Vaillant gas valve replacement with combustion analysis and labor typically costs between €160 and €270.