BoilerFaultCodes .0
This code is not an active error, but rather a menu command used to look up the history of past boiler faults.
Worcester Bosch Greenstar 25i (ZWB 7-25) Fault codes & diagnostics
20 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
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 →
Severity at a glance
Each cell = one fault code. Hover to identify. 12 High
1 Medium
7 Low
Just want the most common Worcester Bosch Greenstar 25i (ZWB 7-25) faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 20 documented codes
Tap any card for details
00 - FF
This is not an error code, but rather a menu screen showing the history of any faults your boiler has experienced in the past.
0.0
Your boiler is currently operating normally, and this message simply shows the last recorded fault from when the system successfully resolved itself.
00h - FFh
Your boiler is currently running through its normal internal health check or diagnostic display mode and is not currently reporting a specific malfunction.
3.3 Your boiler is failing to detect the flame needed to heat your water because the internal sensor is dirty or worn out.
Your boiler is failing to detect the flame needed to heat your water because the internal sensor is dirty or worn out.
Parts commonly replaced
- Ignition electrode
- Ionisation probe
- Gasket kit
5.2 Your boiler has detected an internal communication error with its main control unit, which has caused it to stop working for safety reasons.
Your boiler has detected an internal communication error with its main control unit, which has caused it to stop working for safety reasons.
Parts commonly replaced
- Main printed circuit board (PCB)
- Wiring harness
9.3 Your boiler's main computer control panel is failing to process instructions correctly, which has caused it to stop working for safety reasons.
Your boiler's main computer control panel is failing to process instructions correctly, which has caused it to stop working for safety reasons.
Parts commonly replaced
- Main Electronic Control Unit (PCB)
A1 Your boiler has detected that there is not enough water circulating inside the system to keep it running safely.
Your boiler has detected that there is not enough water circulating inside the system to keep it running safely.
What to check first
- Check the pressure gauge on the front of the boiler; if it is below 1 bar, your system needs to be re-pressurised.
- Locate the external filling loop connected to your boiler and open the valves to allow water in until the gauge reads 1.5 bar.
- Close the filling loop valves tightly and reset the boiler.
Parts commonly replaced
- Central heating pump
- Pressure relief valve
- Expansion vessel
A5 Your boiler is having trouble reading the temperature of the internal hot water store, so it has stopped producing hot water to prevent an error.
Your boiler is having trouble reading the temperature of the internal hot water store, so it has stopped producing hot water to prevent an error.
Parts commonly replaced
- Hot water NTC sensor
- Wiring harness
Ad Your boiler has lost the connection to the sensor that measures the heat inside your hot water storage tank, so it cannot accurately tell when the water is hot.
Your boiler has lost the connection to the sensor that measures the heat inside your hot water storage tank, so it cannot accurately tell when the water is hot.
Parts commonly replaced
- Cylinder NTC sensor
- Wiring harness
Related codes
Showing 11–20 of 20
d1 Your boiler has lost communication with a key internal component that tells it how to regulate your heating and hot water, causing the system to stop working as a precaution.
Your boiler has lost communication with a key internal component that tells it how to regulate your heating and hot water, causing the system to stop working as a precaution.
Parts commonly replaced
- Low Voltage Switch Module
- Main Control Board
- Wiring Harness
E0 Your boiler has detected an internal software or computer glitch that is preventing it from operating correctly.
Your boiler has detected an internal software or computer glitch that is preventing it from operating correctly.
Parts commonly replaced
- Main Electronic Control Board (PCB)
E01 Your boiler has detected a fault and needs to be restarted to try and clear the error.
Your boiler has detected a fault and needs to be restarted to try and clear the error.
What to check first
- Locate the blue 'Reset' button on the front control panel.
- Press and hold the button for approximately three seconds.
- Wait for the boiler to cycle through its internal checks and see if the error light disappears.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Printed circuit board (PCB)
Fault Condition 11
Your boiler is displaying a status that typically indicates the appliance is in a standard standby or operating mode rather than a fault, meaning it is working exactly as it should.
FC Your boiler's electronic display panel is failing to communicate with the internal computer, which prevents the unit from operating normally.
Your boiler's electronic display panel is failing to communicate with the internal computer, which prevents the unit from operating normally.
Parts commonly replaced
- User interface (display) module
- Wiring harness
- Main printed circuit board (PCB)
P1 Your boiler is struggling to begin its initial start-up process, meaning it cannot currently provide heating or hot water until the internal electronic controller is reset or repaired.
Your boiler is struggling to begin its initial start-up process, meaning it cannot currently provide heating or hot water until the internal electronic controller is reset or repaired.
Parts commonly replaced
- Main Control Board (PCB)
- Internal Fuse
- Wiring Harness
P1, P2, P3
Your boiler is currently just running a quick internal startup routine, so please leave it alone for a few moments to see if it clears itself.
P2 Your boiler is struggling to begin its internal startup process, which usually indicates an electrical issue preventing it from turning on safely.
Your boiler is struggling to begin its internal startup process, which usually indicates an electrical issue preventing it from turning on safely.
Parts commonly replaced
- Control Board (PCB)
- Internal Fuse
- Wiring Harness
Related codes
P3 Your boiler is failing to start up properly because it is having trouble completing its internal safety check-up.
Your boiler is failing to start up properly because it is having trouble completing its internal safety check-up.
Parts commonly replaced
- Main PCB
- Control Unit
- Internal Fuse
r1 Your boiler has reverted its custom settings back to the manufacturer's original factory defaults, meaning you may need to re-adjust settings like your heating temperature.
Your boiler has reverted its custom settings back to the manufacturer's original factory defaults, meaning you may need to re-adjust settings like your heating temperature.
What to check first
- Navigate to the boiler's menu and check your heating and hot water temperature settings
- Adjust the settings to your preferred temperatures
- Monitor the boiler to ensure it continues to operate correctly