BoilerFaultCodes 2.4
Your boiler is currently taking a mandatory rest break and will automatically restart on its own after a few minutes.
Worcester Bosch Greenstar 25HE Fault codes & diagnostics
22 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Natural GasLPG 25 kW 2003-2005 Discontinued
Replaced by: Greenstar 25i
Download the Worcester Bosch Greenstar 25HE 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
1 Medium
2 Low
Just want the most common Worcester Bosch Greenstar 25HE faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 22 documented codes
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5.2 Your boiler has detected a problem with its electronic ignition system, meaning it cannot process the command to start the flame safely.
Your boiler has detected a problem with its electronic ignition system, meaning it cannot process the command to start the flame safely.
Parts commonly replaced
- Printed Circuit Board (PCB)
- GFA Ignition Controller
Related codes
9.3 Your boiler’s internal computer has encountered a memory error and cannot safely operate the heater.
Your boiler’s internal computer has encountered a memory error and cannot safely operate the heater.
Parts commonly replaced
- Main PCB (Printed Circuit Board)
- Code Plug
Related codes
24 V fuse blown An internal safety fuse has blown, which has completely disabled your boiler's electronic control system.
An internal safety fuse has blown, which has completely disabled your boiler's electronic control system.
Parts commonly replaced
- Control circuit board PCB
- 24V glass fuse
- Internal wiring loom
Related codes
A1 Your boiler is trying to work but cannot detect enough water moving through the system to operate safely.
Your boiler is trying to work but cannot detect enough water moving through the system to operate safely.
What to check first
- Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.
- If the pressure is too low, use the internal or external filling link to top up the system water.
- Ensure all radiator valves and isolation valves under the boiler are fully open.
- Restart the boiler using the reset button once the pressure is corrected.
Parts commonly replaced
- Circulating Pump
- Automatic Air Vent
- Pressure Sensor
Related codes
A8 Your boiler's internal computer has lost contact with its control panel or external sensors, meaning it cannot receive the instructions it needs to work.
Your boiler's internal computer has lost contact with its control panel or external sensors, meaning it cannot receive the instructions it needs to work.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Display Interface
- Wiring Harness
Related codes
AC Your boiler's main internal computer has lost communication with one of its electronic parts, meaning it cannot operate until the connection is restored.
Your boiler's main internal computer has lost communication with one of its electronic parts, meaning it cannot operate until the connection is restored.
Parts commonly replaced
- PCB (Main Control Board)
- Heatronic Module
- Internal Wiring Harness
Related codes
Ad Your boiler is unable to communicate with its external hot water tank sensor, meaning it doesn't know the temperature of your water.
Your boiler is unable to communicate with its external hot water tank sensor, meaning it doesn't know the temperature of your water.
Parts commonly replaced
- NTC Tank Sensor
- Wiring harness/plug
Related codes
b1 Your boiler's main control chip is either loose or has failed, which means the computer can't identify the specific model to operate safely.
Your boiler's main control chip is either loose or has failed, which means the computer can't identify the specific model to operate safely.
Parts commonly replaced
- Code Plug
- Printed Circuit Board (PCB)
Related codes
C1 Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust fumes.
Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust fumes.
Parts commonly replaced
- Fan assembly
- Printed Circuit Board (PCB)
- Air pressure switch
Related codes
Showing 11–20 of 22
C6 Your boiler has stopped working because the fan that clears away waste gases has failed to start or is spinning too slowly.
Your boiler has stopped working because the fan that clears away waste gases has failed to start or is spinning too slowly.
Parts commonly replaced
- Fan assembly
- Printed Circuit Board (PCB)
- Air pressure switch
Related codes
d3 Your boiler has lost its connection to an external safety device or a plug-in controller, causing it to stop running as a safety precaution.
Your boiler has lost its connection to an external safety device or a plug-in controller, causing it to stop running as a safety precaution.
Parts commonly replaced
- External link plug
- RF receiver
- Internal wiring loom
Related codes
E2 Your boiler's internal thermometer that monitors water temperature has stopped working correctly, causing the system to shut down for safety.
Your boiler's internal thermometer that monitors water temperature has stopped working correctly, causing the system to shut down for safety.
Parts commonly replaced
- Central Heating Flow NTC Sensor
- Connecting Wiring Loom
Related codes
E9 Your boiler has shut down because a sensor has detected that the internal water or exhaust gases have become dangerously hot.
Your boiler has shut down because a sensor has detected that the internal water or exhaust gases have become dangerously hot.
What to check first
- Check that your radiator valves are open and not turned to zero
- Check that your boiler pressure is between 1.0 and 1.5 bar on the pressure gauge
- Press and hold the reset button for five seconds
Parts commonly replaced
- Overheat Thermostat
- Circulating Pump
- Main Heat Exchanger
Related codes
EA Your boiler has failed to light because it cannot detect a flame, which most likely means there is an issue with the gas supply or a part that ignites the fuel.
Your boiler has failed to light because it cannot detect a flame, which most likely means there is an issue with the gas supply or a part that ignites the fuel.
What to check first
- Check that your pre-payment gas meter has credit and is turned on.
- Verify that other gas appliances in your home, like a hob, are working correctly.
- Gently press and hold the 'Reset' button for five seconds to see if the boiler restarts.
- In freezing weather, check if your external plastic condensate pipe has frozen and thaw it with warm water.
Parts commonly replaced
- Ignition Electrode
- Flame Sensing Probe
- Gas Valve
- Printed Circuit Board (PCB)
Related codes
F7 Your boiler thinks a flame is still burning inside even after it has been told to turn off, which is a safety conflict.
Your boiler thinks a flame is still burning inside even after it has been told to turn off, which is a safety conflict.
Parts commonly replaced
- Flame sensing electrode
- Ignition lead
- Printed Circuit Board (PCB)
Related codes
FA Your boiler is still detecting a flame even though it has tried to turn the gas supply off, which is a safety conflict.
Your boiler is still detecting a flame even though it has tried to turn the gas supply off, which is a safety conflict.
Parts commonly replaced
- Gas Valve
- Ionisation Electrode
- Printed Circuit Board (PCB)
Related codes
Fault Your boiler is struggling to burn the gas cleanly, which is causing an internal vibration or rumbling noise that requires professional attention.
Your boiler is struggling to burn the gas cleanly, which is causing an internal vibration or rumbling noise that requires professional attention.
Parts commonly replaced
- Gas valve
- Burner seal kit
- Condensate trap
Related codes
Fd Your boiler is simply confused because the reset button was held down for too long or pressed when it wasn't needed.
Your boiler is simply confused because the reset button was held down for too long or pressed when it wasn't needed.
What to check first
- Press the reset button again firmly once and release it immediately.
- Turn the power to the boiler off at the fused spur switch, wait 30 seconds, and turn it back on.
- If the code persists, wait 30 seconds for the display to clear itself naturally.
Related codes
P1 Your boiler is struggling to start up because a small internal fuse has failed, which prevents the electronic control system from receiving power.
Your boiler is struggling to start up because a small internal fuse has failed, which prevents the electronic control system from receiving power.
Parts commonly replaced
- 24V Fuse
- PCB Control Board
Related codes
Showing 21–22 of 22
P2 Your boiler's electronic control system has detected a failed safety fuse, meaning it cannot start up or provide heating and hot water until this internal electrical component is replaced.
Your boiler's electronic control system has detected a failed safety fuse, meaning it cannot start up or provide heating and hot water until this internal electrical component is replaced.
Parts commonly replaced
- Control board fuse
- Main printed circuit board (PCB)
Related codes
P3 Your boiler is struggling to start up because a small internal fuse responsible for the control electronics has likely failed.
Your boiler is struggling to start up because a small internal fuse responsible for the control electronics has likely failed.
Parts commonly replaced
- Control PCB
- 24V internal fuse
- Wiring harness
Related codes
Status & diagnostic codes 10 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
10 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
.0 Diagnostic The display is simply reminding you that it is ready to show the history of any previous error codes, rather than indicating a current problem with the boiler. 0.0 Diagnostic This is not an active fault code, but a menu setting used by engineers to view the history of previous problems with your boiler. 1. Status Your boiler is performing a routine self-cleaning and safety check to fill up its internal condensate trap. 2. Diagnostic Your boiler is currently running at its maximum power setting as part of its normal automated start-up sequence, so there is no need to worry as this is not a fault. 2.0 Status Your boiler is operating normally and there is nothing wrong with it. 2.5 Diagnostic Your boiler has detected that the water inside the unit is getting too hot and has automatically shut down to prevent damage. 2.6 Diagnostic Your boiler is struggling to maintain a consistent temperature because the difference between the water temperature inside the unit and the temperature setting is too high. 3.3 Diagnostic Your boiler is failing to detect the flame needed to heat your home, so it has safely shut down to prevent gas from building up. 5.0 Diagnostic Your boiler is currently running at its maximum factory power setting during a test or setup phase, which is standard operation rather than a functional breakdown. r1 Diagnostic Your boiler is currently resetting its internal settings back to the way they were when it first left the factory.