Vaillant fault codes associated with the gas valve include F54 (often seen with F28 and F29, suggesting a gas valve issue) and sometimes F28 or F62, although F62 more commonly points to a faulty Printed Circuit Board (PCB) or gas pressure sensor. If you see these codes, check the gas supply, reset the boiler, and if the fault persists, contact a qualified Vaillant engineer as it indicates a complex issue requiring professional attention. 

Common Gas Valve Related Fault Codes

F54:

Often indicates the gas valve needs replacement, especially when seen with F28 and F29. 

F28:

A general ignition failure, which could be caused by an ignition problem or a faulty gas valve. 

F62:

Signifies a delayed switch-off of the gas valve. While it can be a gas valve issue, it's often a fault with the PCB or the gas pressure sensor. 

What to Do if You See These Codes

Check Gas Supply: First, ensure the gas supply is on by checking other gas appliances and the main gas valve.

Reset the Boiler: Try resetting the boiler by pressing the reset button, but be aware that the fault will likely return for more complex issues.

Contact a Professional: If the code persists after checking the gas supply and resetting, it's essential to call a Gas Safe registered engineer. Issues with gas valves and PCBs are complex and require a qualified professional for safe diagnosis and repair.