Water heater shuts down shortly after ignition, display shows overheat / safety thermostat error

Safety first: Turn off electrical power and close the gas shut‑off valve before removing any covers. Allow the unit to cool completely.

Step-by-step checks:

• Reset the safety thermostat: Locate the manual reset safety thermostat (STB) on the top or side of the De Dietrich water heater tank or heat exchanger. Press the red reset button if accessible. Restore power and see if the error clears.
• Check circulation pump operation: When there is a hot water demand, place your hand on the circulation pump body (if external). You should feel vibration and slight warmth. If the pump is cold and silent, check the pump’s power connector and any external pump switch.
• Inspect system pressure (for sealed systems): On models with an integrated expansion vessel, check the pressure gauge. Typical cold pressure is around 1–1.5 bar. If pressure is too low, the system may not circulate properly. Top up via the filling loop according to the installation manual.
• Check for blocked filters: Clean any inline strainers or filters on the cold water inlet and heating circuit return. Debris can restrict flow and cause localized overheating.
• Descale if necessary: Heavy limescale on the primary heat exchanger can cause rapid overheating. If you hear kettling (boiling) noises, the heat exchanger likely needs professional descaling or replacement.

When to call a professional: Persistent E02, repeated tripping of the safety thermostat, or suspected pump/heat exchanger failure should be handled by a qualified De Dietrich technician.