What does the Worcester Bosch E9 error code mean?
E9 means the Worcester boiler's overheat safety thermostat has tripped. It protects the heat exchanger from overheating. Common causes are low system pressure, an airlock, a stuck pump or blocked circulation — some of which you can check first.
What causes the Worcester Bosch E9 fault?
The E9 error on a Worcester Bosch boiler is most commonly triggered by:
- System pressure dropped below 0.5 bar
- Air in the radiators or a blockage preventing circulation
- A weak or seized pump
- A tripped overheat thermostat that needs re-setting once the cause is fixed
How to fix the Worcester Bosch E9 boiler fault
Follow these steps. If the code returns after you have completed them, stop and call a Gas Safe engineer.
- 1.Check the pressure gauge and repressurise to 1.0–1.5 bar if it's low.
- 2.Bleed any air from the radiators and check they're warming evenly.
- 3.If pressure is correct and radiators are balanced and E9 returns, book a Gas Safe engineer to inspect the pump and limit stat.
Frequently asked questions about the Worcester Bosch E9
What does E9 mean on a Worcester Bosch boiler?
E9 is an overheat — the safety limit thermostat has tripped to protect the boiler. It's usually caused by low pressure, air in the system or a circulation fault.
Can I reset an E9 fault myself?
Start by repressurising to 1.0–1.5 bar and bleeding air from the radiators, then press reset. If E9 comes back the pump or thermostat likely needs an engineer.