BoilerFaultCodesViessmann 93 Fault Code
The Viessmann 93 fault code means: your boiler’s solar heating connection has a faulty sensor that is incorrectly detecting a short circuit, preventing your solar panels from helping to heat your water.. It appears on 7 Viessmann models in our database.
Technical description: Control mode - Solar: Sensor S3 shorted out
What causes the Viessmann 93 fault?
This fault occurs when the electrical resistance in the solar temperature sensor falls outside of its normal range, signaling a short circuit to the boiler. The most common reasons are internal failure of the sensor itself or physical damage to the wiring, such as water ingress or frayed cables, which prevents the system from accurately reading the solar tank temperature.
This fault may be more noticeable during the summer months when high temperatures inside the solar circuit can accelerate the wear and tear of aging thermal sensors.
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 93 fault code
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Source
Viessmann 93 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