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Worcester Bosch ZWB 7-25 Fault codes & diagnostics
26 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Natural Gas 25 kW 1997-2003 Discontinued
GC Number 47-311-73
Replaced by: Greenstar 24i / 28i Junior
Download the Worcester Bosch ZWB 7-25 manual
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Severity at a glance
Each cell = one fault code. Hover to identify. 2 Emergency
11 High
1 Low
12 Unrated
Just want the most common Worcester Bosch ZWB 7-25 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 26 documented codes
Tap any card for details
3.3 Your boiler is struggling to detect the flame needed to heat your home and has shut down as a safety precaution.
Your boiler is struggling to detect the flame needed to heat your home and has shut down as a safety precaution.
Parts commonly replaced
- Ignition electrode
- Ionisation probe
- Ignition lead
Related codes
5.2
GFA status / error
9.3
GFA-Asic-error
A1
pump has run dry
A5
Heat store NTC sensor 2 defective
A7 Your boiler is struggling to accurately measure the temperature of the water it is heating, which will likely prevent you from getting hot water through your taps.
Your boiler is struggling to accurately measure the temperature of the water it is heating, which will likely prevent you from getting hot water through your taps.
Parts commonly replaced
- Domestic Hot Water (DHW) NTC Sensor
Related codes
A8 Your boiler's internal control system has lost its connection, meaning it cannot properly talk to its own brain to coordinate heating or hot water.
Your boiler's internal control system has lost its connection, meaning it cannot properly talk to its own brain to coordinate heating or hot water.
Parts commonly replaced
- Control board
- Wiring harness
- Sensor connection
Related codes
AC Your boiler is failing to communicate with its primary control unit, meaning the system cannot start or maintain your heating and hot water.
Your boiler is failing to communicate with its primary control unit, meaning the system cannot start or maintain your heating and hot water.
Parts commonly replaced
- Control board
- Wiring harness
- Interface module
Related codes
Ad
Loose or broken contact on heat store NTC sensor
Showing 11–20 of 26
b1
Keyed plug not detected.
C1 Your boiler has stopped heating because the internal mechanism that pushes air through the system is not spinning fast enough to allow for safe combustion.
Your boiler has stopped heating because the internal mechanism that pushes air through the system is not spinning fast enough to allow for safe combustion.
Parts commonly replaced
- Fan assembly
- Printed Circuit Board (PCB)
Related codes
C6 Your boiler has detected that the internal exhaust fan is spinning faster than it should, so it has shut down as a safety precaution to prevent incorrect combustion.
Your boiler has detected that the internal exhaust fan is spinning faster than it should, so it has shut down as a safety precaution to prevent incorrect combustion.
Parts commonly replaced
- Fan assembly
- Printed Circuit Board (PCB)
Related codes
d3 Your boiler has detected an interruption in a safety circuit, usually meaning a wire or link is disconnected, which prevents the heating from turning on.
Your boiler has detected an interruption in a safety circuit, usually meaning a wire or link is disconnected, which prevents the heating from turning on.
Parts commonly replaced
- External sensor/link
- Wiring harness
- Printed circuit board
Related codes
E2 Your boiler has lost the ability to accurately measure the temperature of the water being sent to your radiators, so it has shut down to prevent overheating.
Your boiler has lost the ability to accurately measure the temperature of the water being sent to your radiators, so it has shut down to prevent overheating.
Parts commonly replaced
- NTC Temperature Sensor
- Wiring harness
Related codes
E9 Your boiler has switched itself off because it has become dangerously hot and needs to cool down to prevent damage.
Your boiler has switched itself off because it has become dangerously hot and needs to cool down to prevent damage.
What to check first
- Check the pressure gauge on the front of the boiler; if it is below 1 bar, top it up to 1.5 bar using the filling link.
- Ensure all radiator valves are fully open to allow water to circulate through the system.
- Press and hold the 'Reset' button for five seconds to see if the error clears once the boiler has cooled down.
Parts commonly replaced
- Limit thermostat
- Pump
- Heat exchanger
Related codes
EA Your boiler has failed to light the flame needed to heat your water and home, so it has safely shut itself down.
Your boiler has failed to light the flame needed to heat your water and home, so it has safely shut itself down.
What to check first
- Check that your gas pre-payment meter (if you have one) has credit.
- Verify that other gas appliances, like a cooker, are receiving gas.
- Press and hold the 'Reset' button for five seconds until the display clears.
- If it is freezing outside, check if the white plastic condensate pipe is frozen and gently thaw it with warm water.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Condensate trap
Related codes
F0 Your boiler has detected an internal software or communication error that is preventing it from operating safely.
Your boiler has detected an internal software or communication error that is preventing it from operating safely.
What to check first
- Press and hold the 'Reset' button for five seconds
- Wait for the boiler to restart and monitor if the code reappears
- Ensure the power supply to the boiler is stable and not fluctuating
Parts commonly replaced
- Control unit
- Printed Circuit Board (PCB)
Related codes
F7 Your boiler has detected a flame signal when it is supposed to be turned off, which suggests a potential fault in the burner control system.
Your boiler has detected a flame signal when it is supposed to be turned off, which suggests a potential fault in the burner control system.
Parts commonly replaced
- Printed circuit board
- Gas valve
- Flame rectification probe
Related codes
FA Your boiler has detected that a flame is still burning inside the unit even though it should have turned off, which is a safety concern that requires an immediate professional check.
Your boiler has detected that a flame is still burning inside the unit even though it should have turned off, which is a safety concern that requires an immediate professional check.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
- Flame rectification probe
Related codes
Showing 21–26 of 26
FC
Textdisplay not detected.
Fd You have accidentally pressed the reset button on your boiler while it was already running normally, so it is just waiting for a few seconds to restart itself.
You have accidentally pressed the reset button on your boiler while it was already running normally, so it is just waiting for a few seconds to restart itself.
What to check first
- Wait for the boiler to complete its automatic restart cycle.
- Do not touch any buttons or controls.
- The display should return to showing the current water temperature within a few minutes.
Related codes
P1
Boiler indicates P1 at start-up
P1, P2, P3, P1...
Please wait, initialisation in progress.
P2
Boiler indicates P2 at start-up
P3
Boiler indicates P3 at start-up