E9
Bosch
Safety High-Limit Overtemperature Trip
Furnace shows E9; unit shuts down due to overheating.
Advertisements
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Advertisements
Possible Causes
Failed circulation pump (hydronic), Blocked system filters or closed valves, Scale buildup in heat exchanger, Faulty high-limit thermostat or sensor
How to Fix / Troubleshooting
Safety: Turn off power. Surfaces and water may be very hot; allow time for cooling.
- System circulation: Ensure all zone valves and radiator valves are open. Check that the Bosch circulation pump runs when there is a call for heat (you should feel vibration or hear it operating).
- Bleed air: Air in the system can stop flow. Bleed radiators and high points as per system design.
- Clean strainers: If your system has a dirt separator or Y-strainer, isolate and clean it.
- High-limit sensor: Locate the high-limit sensor on the flow pipe or heat exchanger. Check wiring and replace the sensor if it is out of specification.
Persistent E9 may indicate a scaled or partially blocked heat exchanger, requiring professional descaling or replacement.
Advertisements
Repair Difficulty
Hard
4/5
Required Part
High-Limit Temperature Sensor
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements