BoilerFaultCodes.com

Worcester Bosch ZB 7 27 HE Fault Codes

System Natural Gas 27 kW 2002-2005 Discontinued
GC Number: 41-311-53

Replaced by: Greenstar 27CDi System

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

A8
Your boiler's computer and its internal controls have stopped talking to each other, causing the unit to stop working for safety.
Gas Safe engineer required · £180-450
AC
Your boiler's main control system is having trouble communicating with an internal plug-in component, meaning it doesn't know how to operate correctly.
Gas Safe engineer required · £120-£350
b1
Your boiler's computer cannot find the physical security chip it needs to know which model it is, preventing the system from starting.
Gas Safe engineer required · £120-£350

All 19 fault codes

Code Severity Plain English
2.2 Low Your boiler is currently set to a specific testing or maintenance mode and is not running in its normal automatic state.
2.4 Low Your boiler is temporarily pausing between firing cycles to prevent the system from turning on and off too frequently, which protects the components from unnecessary wear.
2.5 Medium Your boiler has reached its maximum allowable operating temperature and has temporarily stopped to prevent overheating.
2.6 Low Your boiler has entered a specific maintenance mode or sensor test, meaning it is not operating in its normal heating cycle.
5.0 Low Your boiler is currently running a manual test mode that forces it to operate at its maximum power for maintenance purposes.
A8 High Your boiler's computer and its internal controls have stopped talking to each other, causing the unit to stop working for safety.
AC High Your boiler's main control system is having trouble communicating with an internal plug-in component, meaning it doesn't know how to operate correctly.
b1 High Your boiler's computer cannot find the physical security chip it needs to know which model it is, preventing the system from starting.
C1 High Your boiler's fan is not spinning fast enough to safely clear away exhaust fumes, causing the system to shut down for safety.
C4 High Your boiler's fan is running continuously even when it should be resting, which prevents the system from starting a new heating cycle.
C6 High Your boiler's fan is spinning too fast or the control board cannot regulate its speed, preventing the boiler from starting safely.
E2 High Your boiler has detected a fault with a temperature sensor and has stopped working as a safety precaution.
E9 High Your boiler has effectively switched itself off because it has detected that it is getting too hot, preventing internal damage or unsafe temperatures.
EA High Your boiler is failing to light the gas or cannot confirm that a flame is present, meaning it has shut down for safety.
F0 High Your boiler's internal computer has encountered a major communication error and has stopped working to protect the system.
F7 High Your boiler thinks it can still see a flame inside even though it has been told to turn off, which is a safety conflict that prevents it from starting up again.
FA Emergency Your boiler is still detecting a flame even though it has commanded the gas to turn off, which is a safety conflict.
Fd Low Your boiler is displaying a code simply because the reset button was held down for too long or pressed accidentally.
P1, P2, P3, P1... Low Your boiler is currently performing its startup sequence and check-up, which usually happens after the power has been turned off or the system has been reset.

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 lost its safety connection to an external controller or a safety link is missing, causing the system to stop working for protection.

Worcester Bosch ZB 7 27 HE 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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