Glow-worm [F.29] fault codewhat it means and how to fix it

F.29 is flame loss during operation, with the subsequent attempt to re-ignite also unsuccessful. Separating it from F.28 saves real time. On an F.28 the burner never lit; on an F.29 it did, ran, and then went out. That eliminates the ignition electrode as a primary suspect, because it evidently worked, and it eliminates a total absence of gas, because gas evidently arrived. What is left is a shorter and more specific list. Vaillant Group documentation for this code points at the gas supply being interrupted or at insufficient gas pressure, a fault in the flue gas route caused by recirculation or blockage, and poor electrical earthing. That last one is genuinely worth knowing about, because flame sensing works by passing a tiny current through the flame itself and depends on a sound earth to do so. A degraded earth produces intermittent flame loss that looks inexplicable until somebody tests it, and it is more common in older properties.

1. 1

   Time how long the appliance runs before it drops out, over two or three attempts. Consistency points at condensate; variability points at gas supply or earthing.

2. 2

   Check whether it fails sooner with a gas hob running at full rate. If so, the supply is the likely limitation.

3. 3

   In cold weather, check the external condensate run for ice and thaw it with hand-hot water.

4. 4

   Mention the earthing possibility when you book. It is a listed cause, it is cheap to test, and it is very easily overlooked in favour of replacing parts.

5. 5

   Reset no more than twice and pass on your timing observations.