BoilerFaultCodesSaunier Duval F28 Fault Code
The Saunier Duval F28 fault code means: your boiler has detected that its temperature sensors are giving conflicting readings, which has caused it to stop working for safety.. It appears on 2 Saunier Duval models in our database.
Technical description: Permanent drift between flow sensor and return sensor. Check central heating flow and return thermistor connection. Thermistor defective
What causes the Saunier Duval F28 fault?
This fault occurs when the sensors monitoring the water leaving and returning to your boiler disagree on the temperature by a significant margin. The most common reason is that one of these sensors has become faulty or 'drifted' over time, sending incorrect data to the internal computer. In some cases, it can also be caused by a circulation issue or a failing control board misinterpreting the signals.
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 for a qualified engineer in your area.
Gas Safe Register →Saunier Duval models that show the F28 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Saunier Duval F28 fault code information on this page is sourced and cross-checked against the official Saunier Duval service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026