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.64 is a short on the flow or return NTC input, or a failed analogue input on the PCB. Treat it like F.10 / F.11 first.
Vaillant meaning: Electronics / NTC fault
Possible causes
- Flow NTC shorted
- Return NTC shorted
- Cable short to earth or between cores
- PCB input failed
Possible solutions
- Unplug flow and return NTCs in turn. If F.64 (or F.10 / F.11) clears, that sensor or lead is shorted.
- Measure both NTCs (~12 kΩ at 20 °C).
- Replace the shorted NTC or loom. Replace the PCB only if the inputs still read a short with sensors unplugged.
Possible parts needed
- Flow/return NTC 193592 or 0020068120
- Harness
- PCB
