Worcester Bosch E9 Fault Code: Safety Temperature Limiter Tripped

The E9 fault code on a Worcester Bosch boiler means the safety temperature limiter in the central heating flow has tripped.

What the E9 fault code means

The E9 code is an overheat safety fault. The safety temperature limiter is a device that trips if the water in the heating flow gets too hot. When it trips, the boiler shuts down to prevent damage.

Possible causes of the E9 fault

There are two scenarios:

If the boiler is truly overheating:

• System pressure too low — Not enough water in the system.
• Pump operation — The pump may not be circulating water effectively.
• Air in the system — Trapped air causes poor circulation.
• Blocked heat exchangers — Limescale or sludge build-up.
• Flue overheat or blockage — The flue may be restricted.

If the boiler is NOT truly overheating:

• Continuity on the harness — A wiring fault.
• Primary overheat stat — The thermostat may be faulty.
• Flue stat — The flue thermostat may be faulty.

Can you fix it yourself?

1. Check the system pressure — Make sure it's between 1.0 and 1.5 bar. If low, repressurise using the filling loop.

2. Bleed your radiators — Remove trapped air that can cause poor circulation.

3. Check that all radiator valves are open — Closed valves restrict flow.

4. Reset the boiler — After checking the above, try resetting.

If the E9 code returns, the pump, heat exchanger, or safety thermostat may need attention from a Gas Safe registered engineer. Do not keep resetting — the safety limiter is there for a reason.

Need help with your Worcester Bosch boiler?

Sanju's Heating covers Newbury, Basingstoke and Reading. Call us on 01635 74 50 40 or book online at sanjusheating.co.uk/book

Check our full Worcester Bosch fault code guide for help with other Worcester error codes.