Worcester Bosch Fault Codes — Complete Error Guide for London Homes

Worcester Bosch Boiler Fault Codes — Quick Reference

Worcester Bosch (now branded Worcester Bosch, previously Worcester Bosch Group) is one of the most popular boiler brands in London, particularly their Greenstar range. Their fault codes use a letter-number format. Here are the codes you are most likely to encounter.

EA 227 — Ignition Fault (Most Common)

EA 227 is the most common Worcester Bosch fault code — it means the boiler has failed to ignite after multiple attempts and has gone to lockout. This is the Worcester Bosch equivalent of Vaillant's F.28.

Common causes in London properties:

• Frozen condensate pipe (winter — the condensate pipe running outside may have frozen, blocking the flue and preventing ignition)
• Gas supply interruption (check other gas appliances in the property)
• Faulty ignition electrode or lead — carbon tracking on electrodes is common after several years
• Gas valve fault — worn or stuck gas valve preventing fuel flow to the burner
• PCB (printed circuit board) fault — the control board has failed to send the ignition signal

What to do: First check for a frozen condensate pipe — in winter, this is the most common cause. The condensate pipe is usually a white or grey plastic pipe that exits through an external wall low down. If ice is visible, pour warm (not boiling) water over it to thaw. Then reset the boiler using the reset button (hold for 3 seconds). If the boiler relocks on EA 227 within minutes, call a Gas Safe engineer.

E9 — Overheat/Safety Thermostat

E9 means the boiler's overheat thermostat has tripped. The heat exchanger has reached a temperature above its safe limit and the boiler has shut down.

Common causes: Blocked or scaled heat exchanger (very common in London due to hard water), seized pump, blocked primary circuit (scale, sludge), or closed lockshield valves on radiators restricting flow.

What to do: Allow the boiler to cool for 30 minutes. Attempt one reset. If E9 recurs, do not continue resetting — call a Gas Safe engineer. Repeated E9 events cause permanent heat exchanger damage.

CE 207 — Gas Pressure Fault

CE 207 indicates the gas supply pressure at the boiler is outside the acceptable range. This is either too low (insufficient gas supply) or occasionally too high.

Common causes: National Grid supply interruption in the area, undersized gas supply pipework to the property (common in pre-1970s London terraces), gas meter fault, or a partially closed service valve.

What to do: Check whether other gas appliances (hob, gas fire) are working. If nothing gas-powered works, check with neighbours — it may be a street supply issue. If it is boiler-specific, call a Gas Safe engineer. Do not attempt to adjust gas valves or meters yourself.

H07 — External Controls Fault

H07 means the boiler is receiving a conflicting signal from external controls — typically a room thermostat, programmer or smart thermostat system that is giving incompatible commands.

Common causes: Smart thermostat (Nest, Hive, tado°) incompatibility after a software update, a failed room thermostat sending continuous or no signal, or a wiring fault in the external controls.

What to do: Check your room thermostat and programmer are both set correctly. If using a smart thermostat, check the app and ensure the system is connected to WiFi. Try temporarily removing the external controls from the equation (bridge the room thermostat terminals) to confirm this is the fault source. Call a Gas Safe engineer to diagnose wiring issues.

240 — Condensate Drain Blocked

Fault code 240 on Worcester Bosch boilers specifically indicates a condensate drainage problem — the condensate trap is blocked or the pipe is frozen.

Fix for frozen condensate (most common in winter): As with EA 227, pour warm water over the external pipe until it thaws, then reset the boiler.

Worcester Bosch Reset Procedure

On most Worcester Bosch Greenstar models, press and hold the reset button (usually a flame symbol on the right side of the display) for 3-5 seconds until the display changes. The boiler will attempt to restart. If the fault code returns within 10 minutes, do not continue resetting — you risk further damage.