Controller displays E03 and boiler shuts down on high temperature before reaching setpoint.

Safety: Turn off power and allow the Danstoker boiler to cool completely. Do not reset high-limit devices on a hot boiler.

• Check system pressure and circulation: Verify that the system pressure is within the recommended range on the boiler pressure gauge. Listen/feel for operation of the primary circulation pump. Bleed air from high points and air vents to remove air locks.
• Reset high-limit thermostat: Locate the manual reset high-limit thermostat on the boiler front or control panel (often a red button). Once the boiler is cool, press to reset. If it trips repeatedly, do not continue resetting without finding the cause.
• Inspect temperature sensor: Check the wiring to the boiler flow temperature sensor (NTC or PT100) used by the Danstoker controller. Look for loose or corroded terminals. Replace the sensor if readings are clearly incorrect compared to an external thermometer.
• Check for scale or fouling: If the boiler is older or operating with hard water, internal scaling in the Danstoker heat exchanger can cause localized overheating. Look for signs of kettling (rumbling noise). Descaling or mechanical cleaning may be required by a professional.

If E03 persists, contact a heating technician to test sensors, verify pump performance, and inspect the heat exchanger.