F28
FAULT CODE
Saunier Duval
Permanent Flow/Return Sensor Drift (Thema)
Medium Severity
Engineer Required
On Saunier Duval Thema boilers, F28 indicates a permanent temperature drift between the flow and return sensors — possible sensor fault.
Step-by-Step Fix Guide
-
Step 1 Engineer only
Call a Gas Safe engineer to test both thermistors and check their connections
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.