Gas Safe: Gas work, flue work, and PCB replacement on a gas boiler must be carried out by a Gas Safe registered engineer. Homeowners can check obvious items such as heating pressure, condensate overflow, and whether a control is unplugged — then call an engineer.
Always confirm the part number against the boiler GC number and the installation manual before ordering.
Overview
F.68 is a flame that will not sit still on the ionisation circuit: gas, air ratio, condensate, electrode, or recirculation. It is the “running” cousin of F.28 / F.29.
Vaillant meaning: Unstable flame signal
Possible causes
- Air in the gas or low inlet pressure
- Wrong air ratio / restrictor / gas family
- Blocked condensate route
- Ionisation lead or electrode intermittent
- Flue-gas recirculation (flue joint, terminal, or heat exchanger)
Possible solutions
- Check meter and appliance working pressure. Purge if the supply was off.
- Clear condensate trap, siphon, and outlet. Frozen or blocked condensate is a very common F.68 / F.28 pair.
- Inspect and replace the electrode and lead if oxidised or loose.
- Check flue joints and the heat-exchanger / burner door seal for recirculation.
- Combustion analyse and set CO/CO₂ to the table. Wrong restrictor or gas family also shows as F.93.
Possible parts needed
- Electrode 090709 or 0020133816
- Ignition lead
- Condensate trap / siphon
- Burner door gasket / flue seals
- Gas valve or restrictor only if combustion cannot be set
