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.03 is an open circuit on the actoSTOR cylinder (store) NTC, again only with F.91. The store temperature is not being read.
Vaillant meaning: Interruption cylinder sensor actoSTOR (NTC) — only in combination with F.91
Possible causes
- Cylinder NTC defective or unplugged
- NTC cable damaged
- Poor plug on NTC or actoSTOR electronics
Possible solutions
- Confirm actoSTOR is fitted and F.91 is present.
- Check the cylinder NTC is fully home in its pocket and plugged in.
- Measure the NTC, then the lead, then the actoSTOR electronics.
Possible parts needed
- actoSTOR cylinder NTC (confirm GC / parts list)
- NTC cable / harness
- actoSTOR electronics module