BoilerFaultCodes .0
Your boiler is simply displaying the history of the last recorded technical fault for your engineer to review.
Worcester Bosch ZB 7 27 HE Fault codes & diagnostics
24 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
System Natural Gas 27 kW 2015 onwards Discontinued
GC Number 41-311-58
Download the Worcester Bosch ZB 7 27 HE manual
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The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
Severity at a glance
Each cell = one fault code. Hover to identify. 2 Emergency
17 High
2 Medium
3 Low
Just want the most common Worcester Bosch ZB 7 27 HE faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 24 documented codes
Tap any card for details
5.2 Your boiler's internal computer is reporting an error during its startup process, which prevents it from safely igniting and providing heat or hot water.
Your boiler's internal computer is reporting an error during its startup process, which prevents it from safely igniting and providing heat or hot water.
Parts commonly replaced
- Gas valve
- Printed circuit board (PCB)
- Wiring harness
Related codes
9.3 Your boiler has detected a critical internal electronic failure, meaning it cannot communicate correctly with itself to operate safely.
Your boiler has detected a critical internal electronic failure, meaning it cannot communicate correctly with itself to operate safely.
Parts commonly replaced
- Main circuit board (PCB)
A1 Your boiler has detected that there is not enough water circulating inside the system, which can cause the pump to overheat and fail.
Your boiler has detected that there is not enough water circulating inside the system, which can cause the pump to overheat and fail.
Parts commonly replaced
- Central heating pump
- Pressure sensor
- Expansion vessel
Related codes
A5 Your boiler is having trouble measuring the temperature of the internal hot water storage, which may prevent it from providing hot water correctly.
Your boiler is having trouble measuring the temperature of the internal hot water storage, which may prevent it from providing hot water correctly.
Parts commonly replaced
- Hot water cylinder NTC sensor
- Wiring harness
Related codes
A7 Your boiler is struggling to accurately measure the temperature of the water it is heating, so it has stopped producing hot water to prevent it from getting too hot.
Your boiler is struggling to accurately measure the temperature of the water it is heating, so it has stopped producing hot water to prevent it from getting too hot.
Parts commonly replaced
- Domestic hot water NTC sensor
Related codes
A8 Your boiler has lost the ability for its internal parts to 'talk' to each other, so it has shut down to prevent errors.
Your boiler has lost the ability for its internal parts to 'talk' to each other, so it has shut down to prevent errors.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Communication wiring loom
Related codes
AC Your boiler's electronic control system is failing to communicate with its internal components, causing the system to shut down for safety.
Your boiler's electronic control system is failing to communicate with its internal components, causing the system to shut down for safety.
Parts commonly replaced
- Control module
- PCB
- Wiring harness
Related codes
Ad Your boiler has lost its connection to the sensor that measures how hot your stored hot water is, so it may stop heating your hot water cylinder.
Your boiler has lost its connection to the sensor that measures how hot your stored hot water is, so it may stop heating your hot water cylinder.
Parts commonly replaced
- Cylinder NTC sensor
- Wiring harness
Related codes
b1 Your boiler's control panel has lost its connection to a crucial internal safety plug, meaning the system cannot communicate properly to function.
Your boiler's control panel has lost its connection to a crucial internal safety plug, meaning the system cannot communicate properly to function.
Parts commonly replaced
- Keyed plug
- Wiring harness
- Printed Circuit Board
Related codes
Showing 11–20 of 24
C1 Your boiler is struggling to push air through its internal system effectively, which stops it from firing up safely.
Your boiler is struggling to push air through its internal system effectively, which stops it from firing up safely.
Parts commonly replaced
- Fan assembly
- Air pressure switch
- Flue system components
Related codes
CC Your boiler has detected an internal communication or sensor issue and has safely shut down to prevent any further problems.
Your boiler has detected an internal communication or sensor issue and has safely shut down to prevent any further problems.
Parts commonly replaced
- PCB
- Wiring harness
- Control sensor
Related codes
d3 Your boiler has lost the connection to its external thermostat or control unit, preventing it from knowing when to turn the heating on.
Your boiler has lost the connection to its external thermostat or control unit, preventing it from knowing when to turn the heating on.
Parts commonly replaced
- Link wire
- PCB
- External programmer
Related codes
E2 Your boiler's temperature sensor is providing faulty information, causing the system to stop heating for safety reasons.
Your boiler's temperature sensor is providing faulty information, causing the system to stop heating for safety reasons.
Parts commonly replaced
- NTC Temperature Sensor
- Wiring harness
Related codes
E9 Your boiler has detected that it is running too hot and has automatically shut down to prevent damage to the internal system.
Your boiler has detected that it is running too hot and has automatically shut down to prevent damage to the internal system.
Parts commonly replaced
- NTC Sensor
- Primary Heat Exchanger
- Pump
- PCB
Related codes
EA Your boiler is trying to start but the flame is failing to light or stay lit, so it has shut itself off for safety.
Your boiler is trying to start but the flame is failing to light or stay lit, so it has shut itself off for safety.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Flame rectification probe
Related codes
F0 Your boiler has detected a critical internal software or hardware error and has shut itself down as a safety precaution.
Your boiler has detected a critical internal software or hardware error and has shut itself down as a safety precaution.
Parts commonly replaced
- Main control board (PCB)
- Wiring harness
Related codes
F7 Your boiler has detected a flame signal when it shouldn't be running, meaning the system is confused about whether it is on or off.
Your boiler has detected a flame signal when it shouldn't be running, meaning the system is confused about whether it is on or off.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Flame detection electrode
- Gas valve
Related codes
FA Your boiler has detected that a flame is still burning inside even though it has commanded the gas supply to turn off, which is a significant safety concern.
Your boiler has detected that a flame is still burning inside even though it has commanded the gas supply to turn off, which is a significant safety concern.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
- Flame rectification electrode
Related codes
Fd Your boiler has detected that the reset button was pressed unnecessarily and is simply indicating that no actual fault has occurred.
Your boiler has detected that the reset button was pressed unnecessarily and is simply indicating that no actual fault has occurred.
What to check first
- Wait for the boiler to return to its normal standby mode
- If the code persists, restart the boiler using the main power switch
- Monitor the display to ensure the standard temperature readout returns
Showing 21–24 of 24
P1 Your boiler is failing to begin its start-up process, which means it cannot trigger the ignition to provide you with heating or hot water.
Your boiler is failing to begin its start-up process, which means it cannot trigger the ignition to provide you with heating or hot water.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Internal Fuse
- Wiring Harness
Related codes
P1, P2, P3, P1... Your boiler is simply performing a temporary startup check and restarting its initialisation process.
Your boiler is simply performing a temporary startup check and restarting its initialisation process.
Related codes
P2 Your boiler is failing to begin its internal ignition process, meaning it cannot provide heating or hot water until a technical fault is cleared.
Your boiler is failing to begin its internal ignition process, meaning it cannot provide heating or hot water until a technical fault is cleared.
Parts commonly replaced
- Control PCB
- Internal fuse
- Wiring harness
Related codes
P3 Your boiler is failing to begin its start-up process, meaning it cannot ignite to provide you with heating or hot water.
Your boiler is failing to begin its start-up process, meaning it cannot ignite to provide you with heating or hot water.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Internal Fuses
- Wiring Harness
Related codes
Status & diagnostic codes 7 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
7 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
2.0 Diagnostic Your boiler is currently in a manual testing mode used by engineers to check its performance rather than a standard fault, meaning it is not operating normally for your home heating. 2.2 Diagnostic Your boiler is struggling to circulate water properly because it cannot communicate correctly with its internal water pump. 2.4 Diagnostic Your boiler is perfectly fine, it is simply pausing for a few minutes between heating cycles to save energy and prevent unnecessary wear. 2.5 Diagnostic Your boiler has detected that the water inside is getting too hot and has temporarily switched itself off to prevent damage. 2.6 Diagnostic Your boiler is struggling to maintain a consistent temperature because the difference between the target heat set on your programmer and the actual water temperature is too large. 5.0 Diagnostic Your boiler is currently set to run at its maximum heating capacity, which is typical during a start-up or testing cycle rather than a permanent fault. r1 Diagnostic Your boiler is currently performing an internal reset to restore its factory service settings, which is a normal process and not an actual error.