Vaillant F28 F29: Causes, Differences and Boiler Repair Guide

Understanding the difference between the two codes is relatively straightforward.

F28 generally means ignition failure: the boiler cannot establish a flame when attempting to start.

F29 generally means flame loss: the boiler has established a flame but loses it while operating.

Both faults can leave a property without heating or hot water, and both can have multiple possible causes. This is why professional diagnosis is preferable to simply replacing parts based on the error code alone.

Common Causes of Vaillant F28

There are several potential reasons for an F28 fault.

Gas Supply Issues

The boiler needs a suitable gas supply to ignite and operate correctly. An interruption or problem with the gas supply can prevent successful ignition.

If other gas appliances in the property are also affected, the issue may not be limited to the boiler itself.

Ignition Problems

The ignition system is responsible for helping establish the burner flame. If an ignition component develops a fault, the boiler may fail to start and display F28.

The relevant components should be inspected by a suitably qualified heating engineer.