Applicable Systems
Greenstar GB162
Symptoms
The Worcester Bosch Greenstar boiler displays fault code E9, indicating overheating. The boiler has shut down because a safety temperature limiter has detected that the heat exchanger or system temperature exceeds the safe limit.
Possible Causes
- System circulation pump failed or running at reduced speed
- System filter or pipework blocked restricting water flow through the heat exchanger
- Air in the heating system causing poor circulation
- Temperature limiter (safety thermostat) faulty giving false reading
Troubleshooting Steps
- Step 1: Check system pressure on the boiler pressure gauge
Pressure must be between 1.0 and 2.0 bar when cold; repressurize if below 1.0 bar using the filling loop - Step 2: Verify circulation pump is running and not blocked
Pump should vibrate slightly when running; check for seized pump or air lock - Step 3: Bleed radiators and check for air in the heating system
Air in the system causes circulation problems; bleed all radiators starting from the lowest - Step 4: Inspect system filter and magnetic sludge separator for blockage
Clean or replace filter elements; sludge buildup restricts flow and causes overheating
How to Reset
To reset: 1) Press and hold the Reset button on the boiler fascia for approximately 5 seconds. 2) The boiler should restart. 3) If E9 returns, the overheating cause must be investigated by a Gas Safe registered engineer. Caution: Repeated E9 faults indicate a circulation problem that can damage the heat exchanger permanently.
Frequently Asked Questions
- Q: What temperature triggers E9 on a Worcester Bosch boiler?
E9 triggers when the safety temperature limiter detects the heat exchanger temperature exceeds approximately 95-105C. The exact threshold varies by model.
- Q: Can I reset E9 myself?
Yes, you can press the reset button. However, if E9 recurs, you must contact a Gas Safe registered engineer. Repeated overheating can cause permanent heat exchanger damage and is a safety concern.
Source: Worcester Bosch GB162 Installation and Servicing Instructions, Fault Code E9, Worcester Bosch UK Documentation
Category: Home Boiler