BoilerFaultCodes.com

Worcester Bosch Greenstar 25i (ZWB 7-25) Fault Codes

Combi Natural Gas 25 kW 2005-2015 Discontinued
GC Number: 47-116-60

Replaced by: Greenstar 25i (2015-2021) / Greenstar 4000

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Most common fault codes

A7
Your boiler is struggling to accurately measure the temperature of your hot water, which usually means your taps will only run cold or keep fluctuating in temperature.
Gas Safe engineer required · £90-160
A8
Your boiler's main control board has lost connection with its internal components or the external thermostat, meaning it cannot receive the instructions it needs to run.
Gas Safe engineer required · £120-£450
AC
Your boiler's main control board has lost communication with an internal module or plug-in component, causing the system to stop working.
Gas Safe engineer required · £180-£450

All 16 fault codes

Code Severity Plain English
A7 High Your boiler is struggling to accurately measure the temperature of your hot water, which usually means your taps will only run cold or keep fluctuating in temperature.
A8 High Your boiler's main control board has lost connection with its internal components or the external thermostat, meaning it cannot receive the instructions it needs to run.
AC High Your boiler's main control board has lost communication with an internal module or plug-in component, causing the system to stop working.
b1 High Your boiler's internal computer memory chip is not being detected, which has caused the system to shut down for safety.
C1 High Your boiler has stopped working because the internal fan, which clears away exhaust fumes, is not spinning at the correct speed.
C4 High Your boiler's fan is running continuously or failing to stop, which prevents the system from starting a new heating cycle safely.
C6 High Your boiler's fan is spinning too fast or working incorrectly, forcing the system to shut down for safety.
CC Low Your boiler has lost connection to its outdoor temperature sensor, which helps it run efficiently based on the weather outside.
E2 High Your boiler has detected a faulty internal temperature sensor, which means it cannot accurately monitor the water temperature and has stopped working for safety.
E9 High Your boiler has shut down because it has detected an unsafe build-up of heat or a lack of water circulation within the main unit.
EA High Your boiler has tried to ignite but cannot detect a flame, which means it has stopped working to prevent a safety issue.
F0 High Your boiler has encountered a computer glitch on its main control board and cannot function until it is reset or repaired.
F7 High Your boiler is still detecting a flame even though it has been told to turn off, which is a safety conflict that prevents it from running.
FA Emergency Your boiler is still detecting a flame even though it has tried to turn the gas supply off, which is a safety conflict.
Fd Low Your boiler has stopped because the reset button was pressed accidentally or held down for too long.
P1, P2, P3, P1... Low Your boiler is simply starting up and checking its internal systems, which is a normal part of its power-on sequence.

Status & diagnostic codes

These codes indicate your boiler's operating state or a diagnostic reading — not necessarily a fault. Status codes (S.) mean normal operation; diagnostic codes (D.) are informational readings used by engineers.

Code Type Description
d3 Diagnostic Your boiler has detected that a safety device or a control link has been triggered or disconnected, causing the system to shut down to prevent overheating.

Worcester Bosch Greenstar 25i (ZWB 7-25) is discontinued — time for a new one?

Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.

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