Furnace locks out with A03, overheat condition, boiler very hot to touch

Safety: Switch off power and allow the Brötje furnace to cool completely. Do not reset repeatedly without finding the cause of overheating.

• 1. Check system pressure: On the boiler’s pressure gauge, verify that the heating system pressure is within the recommended range (typically around 1.2–1.8 bar when cold). If low, top up via the filling loop according to the manual and bleed radiators.
• 2. Verify circulation pump operation: With power restored, set the boiler to call for heat. Touch the circulation pump body (carefully). It should vibrate slightly and get warm. If it hums but does not turn, the pump may be seized. Try freeing the shaft via the pump’s vent screw (if present). Replace the Brötje circulation pump if it does not run.
• 3. Clean system filter and strainers: Locate any dirt separator or Y-strainer on the return line. Isolate, depressurise, and clean the filter insert. A blocked filter can cause no flow and overheating.
• 4. Bleed air from system: Bleed air from radiators and any automatic air vents near the boiler. Air locks can stop circulation and cause rapid temperature rise.
• 5. Check STB (safety temperature limiter): Locate the manual reset button on the STB (often on the flow pipe or heat exchanger). After cooling, press to reset. If it trips again quickly, do not continue resetting—find and fix the underlying flow problem.

If the STB or flow sensor is defective, or if the heat exchanger is heavily scaled or blocked, contact a Brötje service technician for replacement and system flushing.