BoilerFaultCodesViessmann 38 Fault Code
The Viessmann 38 fault code means: your boiler has stopped working because it cannot accurately measure its own internal temperature due to a broken or disconnected sensor wire.. It appears on 9 Viessmann models in our database.
Technical description: Burner blocked - Boiler temperature sensor lead break
What causes the Viessmann 38 fault?
This fault occurs when the boiler's main internal thermometer stops sending a steady electrical signal to the control board. The most common reason is a physical break in the thin copper wiring or a connector that has vibrated loose, preventing the boiler from knowing its own temperature. Because the boiler cannot safely monitor if it is overheating, it shuts down the burner as a safety precaution.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the 38 fault code
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Source
Viessmann 38 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026