Medium
F.13 on Vaillant Home System

Your boiler has lost communication with the hot water cylinder temperature sensor because of an electrical fault, meaning it cannot safely tell if your water is hot enough.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Short circuit: Domestic hot water cylinder temperature sensor. Possible cause: NTC sensor defective, short circuit in the cable harness, cable/casing

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related fault codes

F.10View →F.11View →

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on combis.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →