BoilerFaultCodesViessmann 53:3 Fault Code
Also written as 533 — same fault.
The Viessmann 53:3 fault code means: your boiler is having trouble communicating with the pump that fills your separate hot water tank, meaning your home's hot water supply may be affected.. It appears on 5 Viessmann models in our database.
Technical description: Function relay 2: External cylinder loading pump
What causes the Viessmann 53:3 fault?
This fault occurs when the boiler's control system loses its electrical connection to the pump responsible for heating your hot water tank. The most common reasons are a loose or damaged connection in the internal wiring harness, a failure of the relay module that sends power to the pump, or the pump's motor itself drawing too much current and causing a communication error.
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 53:3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 53:3 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