BoilerFaultCodes .0
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.
Worcester Bosch Greenstar 25HE Fault codes & diagnostics
47 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Natural GasLPG 25 kW 2003-2005 Discontinued
GC Number 47-311-32
Replaced by: Greenstar 25i
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
23 High
5 Medium
17 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 47 documented codes
Tap any card for details
0.0 This is not an active fault code, but a menu setting used by engineers to view the history of previous problems with your boiler.
This is not an active fault code, but a menu setting used by engineers to view the history of previous problems with your boiler.
What to check first
- Press the reset button to return the boiler to its normal display mode
- If the boiler is working normally, no further action is required
- If the boiler is not working, check for other flashing codes on the display
Related codes
1. Your boiler is performing a routine self-cleaning and safety check to fill up its internal condensate trap.
Your boiler is performing a routine self-cleaning and safety check to fill up its internal condensate trap.
What to check first
- Wait for approximately 10 to 20 minutes for the programme to finish automatically.
- Do not turn the boiler off during this process.
- The boiler will return to normal operation and show its usual temperature display once complete.
2.
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 Your boiler is operating normally and there is nothing wrong with it.
Your boiler is operating normally and there is nothing wrong with it.
What to check first
- No action required as the boiler is functioning as intended
2.4
Your boiler is currently taking a mandatory rest break and will automatically restart on its own after a few minutes.
2.5 Your boiler has detected that the water inside the unit is getting too hot and has automatically shut down to prevent damage.
Your boiler has detected that the water inside the unit is getting too hot and has automatically shut down to prevent damage.
Parts commonly replaced
- NTC Temperature Sensor
- Circulation Pump
- Printed Circuit Board (PCB)
Related codes
2.6 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.
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.
Parts commonly replaced
- NTC Temperature Sensor
- PCB (Printed Circuit Board)
- Flow / Return thermistors
3.3 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.
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.
Parts commonly replaced
- Ignition electrode
- Ionisation probe
- Printed Circuit Board (PCB)
Related codes
5.0
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.
Showing 11–20 of 47
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
45 -- 45 Your boiler is currently running in a special test mode or minimum power setting, which is not a standard fault.
Your boiler is currently running in a special test mode or minimum power setting, which is not a standard fault.
What to check first
- Check if the service/test mode switches have been left in the 'Min' position
- Press the reset button to return to normal operation
- Turn the boiler off and back on at the fused spur to reboot the system
Parts commonly replaced
- Control board
- PCB
55 -- 55 Your boiler is currently running at its absolute maximum capacity because it has been set to a special testing mode, rather than operating normally to heat your home.
Your boiler is currently running at its absolute maximum capacity because it has been set to a special testing mode, rather than operating normally to heat your home.
Parts commonly replaced
- Control board
- PCB
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
A5 Your boiler's temperature sensor responsible for monitoring stored hot water has developed a fault, preventing it from reading the temperature correctly.
Your boiler's temperature sensor responsible for monitoring stored hot water has developed a fault, preventing it from reading the temperature correctly.
Parts commonly replaced
- NTC thermistor sensor
- Wiring harness connector
Related codes
A7 Your boiler is struggling to accurately measure the temperature of your hot water, which usually means it cannot provide a consistent warm flow to your taps.
Your boiler is struggling to accurately measure the temperature of your hot water, which usually means it cannot provide a consistent warm flow to your taps.
Parts commonly replaced
- Domestic Hot Water (DHW) NTC Sensor
- Wiring Harness connection
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
Showing 21–30 of 47
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
C4 Your boiler's fan is spinning faster than it should, which means the system has stopped running to prevent any damage or unsafe operation.
Your boiler's fan is spinning faster than it should, which means the system has stopped running to prevent any damage or unsafe operation.
Parts commonly replaced
- Fan assembly
- Printed Circuit Board (PCB)
- Harness wiring
Related codes
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
d1 Your boiler is struggling to monitor the temperature of the water returning to it, which is preventing the heating system from working correctly.
Your boiler is struggling to monitor the temperature of the water returning to it, which is preventing the heating system from working correctly.
Parts commonly replaced
- Low Loss Header Sensor
- Wiring harness
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
F0 Your boiler's computer brain has suffered a serious internal glitch and is unable to communicate with its own sensors or controls.
Your boiler's computer brain has suffered a serious internal glitch and is unable to communicate with its own sensors or controls.
What to check first
- Locate the reset button on the front control panel
- Press and hold the reset button for five seconds
- Release the button and wait for the boiler to restart
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Wiring harness
Related codes
Showing 31–40 of 47
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
FC Your boiler's main control panel has lost communication with the internal computer, meaning the display cannot show information or process commands.
Your boiler's main control panel has lost communication with the internal computer, meaning the display cannot show information or process commands.
Parts commonly replaced
- Display PCB
- Main Power Interface PCB
- Wiring Harness
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
None Your boiler is likely suffering from a build-up of limescale or sludge inside the heat exchanger, causing it to vibrate or 'kettle' like a noisy tea kettle.
Your boiler is likely suffering from a build-up of limescale or sludge inside the heat exchanger, causing it to vibrate or 'kettle' like a noisy tea kettle.
Parts commonly replaced
- Main Heat Exchanger
- Circulating Pump
- Condensate Trap
Related codes
P1 Your boiler is repeatedly trying and failing to complete its ignition process, essentially getting stuck in a loop during startup.
Your boiler is repeatedly trying and failing to complete its ignition process, essentially getting stuck in a loop during startup.
Parts commonly replaced
- Ignition Lead
- Spark Electrode
- Flame Sensing Electrode
- Gas Valve
Related codes
P1, P2, P3 Your boiler is struggling to start up correctly and keeps getting stuck in a repeated reset loop, preventing it from heating your home.
Your boiler is struggling to start up correctly and keeps getting stuck in a repeated reset loop, preventing it from heating your home.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Flue sensor
- Wiring harness
Related codes
P1, P2, P3, P1... Your boiler is simply going through its normal startup and self-test sequence after being turned on or reset.
Your boiler is simply going through its normal startup and self-test sequence after being turned on or reset.
What to check first
- Wait for approximately 30 to 60 seconds for the sequence to finish
- Ensure the boiler power is left switched on
- If the code persists for more than 5 minutes, try a single reset
P2 Your boiler is currently going through its normal starting process but is taking a little longer than usual to fully ignite.
Your boiler is currently going through its normal starting process but is taking a little longer than usual to fully ignite.
What to check first
- Wait 15 minutes to see if the code clears automatically
- Check that your gas supply is active and turned on
- Reset the boiler by pressing and holding the reset button for 5 seconds
Parts commonly replaced
- Ignition Electrode
- Spark Cable
Related codes
Showing 41–47 of 47
P3 Your boiler is simply showing that it is going through its normal starting process and trying to fire up.
Your boiler is simply showing that it is going through its normal starting process and trying to fire up.
What to check first
- Wait for the boiler to complete its start-up sequence
- Check that your thermostat is calling for heat
- Ensure the gas supply is turned on if the code persists
Related codes
P4 Your boiler is currently running its own internal health check as it starts up and may just need a moment to finish.
Your boiler is currently running its own internal health check as it starts up and may just need a moment to finish.
What to check first
- Wait up to 10 minutes for the self-test to complete
- Ensure the power cycles correctly if you have recently turned the boiler off and on
- Monitor the display to see if it transitions to a normal temperature reading
Parts commonly replaced
- None (Software sequence)
- Control board (if stuck indefinitely)
Related codes
P5 Your boiler is simply running a routine internal check as it starts up and there is no actual fault with the appliance.
Your boiler is simply running a routine internal check as it starts up and there is no actual fault with the appliance.
What to check first
- Wait for approximately 30 to 60 seconds for the code to disappear naturally
- Ensure the power supply to the boiler remains switched on during this process
- If the code stays on the screen for several minutes, try pressing the reset button once
Related codes
P6 Your boiler is simply performing a routine internal check as it starts up and the code should disappear after a few seconds.
Your boiler is simply performing a routine internal check as it starts up and the code should disappear after a few seconds.
What to check first
- Wait for 30-60 seconds to see if the code clears automatically
- Ensure the power supply to the boiler is stable
- Reset the boiler if the code remains on the screen for more than 2 minutes
Related codes
r1 Your boiler is currently resetting its internal settings back to the way they were when it first left the factory.
Your boiler is currently resetting its internal settings back to the way they were when it first left the factory.
What to check first
- Wait for the boiler to complete the reset process naturally
- Once finished, the display should return to the normal temperature reading
- Re-adjust your heating and hot water temperature dials to your preferred levels if they have changed
r2
Your boiler is currently in the middle of a internal software reset process and is not experiencing a fault.
Red light Your boiler has stopped working and entered a safety shutdown mode, likely because it hasn't been used for a while or has failed to ignite.
Your boiler has stopped working and entered a safety shutdown mode, likely because it hasn't been used for a while or has failed to ignite.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Printed Circuit Board (PCB)
Related codes
Status & diagnostic codes 1 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.
1 operating states & engineer diagnostics
Not faults — these are normal operating states. Tap to expand.