BoilerFaultCodes 200
Your boiler is operating normally and is currently heating your radiators.
Worcester Bosch Greenstar 8000 Style GR8700iW 35 S Fault codes & diagnostics
32 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
System Natural GasLPG 2018-present
GC Numbers 41-406-8641-406-88
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Severity at a glance
Each cell = one fault code. Hover to identify. 2 Emergency
19 High
4 Medium
7 Low
Fault codes
All 32 documented codes
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201
Your boiler is currently operating normally to heat your hot water, and there is no fault present.
202
Your boiler is perfectly safe and simply taking a short break to prevent its internal components from wearing out too quickly after your heating was recently turned off.
203 Your boiler is perfectly healthy and simply waiting for a signal from your thermostat to turn on the heating or hot water.
Your boiler is perfectly healthy and simply waiting for a signal from your thermostat to turn on the heating or hot water.
What to check first
- Turn up your room thermostat or smart controller settings
- Check that your hot water timer or programmer is set to 'On'
- Wait for a few minutes to see if the boiler fires up once a heat request is sent
204 Your boiler has sensed that the water temperature has risen above the level it was set to reach, leading it to shut down for safety.
Your boiler has sensed that the water temperature has risen above the level it was set to reach, leading it to shut down for safety.
What to check first
- Check that all radiator valves are fully open to allow water to circulate.
- Ensure there is enough water pressure in the system by checking the digital gauge.
- Restart the boiler using the reset button on the touch screen.
Parts commonly replaced
- Circulation Pump
- Flow Temperature Sensor (NTC)
- Main Heat Exchanger (Cleaning)
Related codes
208 Your boiler has been accidentally switched into a testing mode used by engineers to check emissions, which prevents it from heating your home normally.
Your boiler has been accidentally switched into a testing mode used by engineers to check emissions, which prevents it from heating your home normally.
What to check first
- Locate the chimney sweep button on your boiler's front control panel.
- Press and hold the chimney sweep button for approximately 5 seconds.
- Wait for the display to return to the standard temperature reading and ensure the boiler resumes normal operation.
224 Your boiler has switched itself off because it has detected an unsafe rise in internal temperature and needs to be inspected by a professional.
Your boiler has switched itself off because it has detected an unsafe rise in internal temperature and needs to be inspected by a professional.
Parts commonly replaced
- NTC temperature sensor
- Primary heat exchanger
- Pump
Related codes
227 Your boiler is attempting to start but is unable to detect a steady flame, so it has safely shut down to prevent gas from escaping.
Your boiler is attempting to start but is unable to detect a steady flame, so it has safely shut down to prevent gas from escaping.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Printed Circuit Board (PCB)
Related codes
228 Your boiler has detected a sensor error where it believes a flame is present when it isn't, and it has safely locked itself out to prevent any issues.
Your boiler has detected a sensor error where it believes a flame is present when it isn't, and it has safely locked itself out to prevent any issues.
Parts commonly replaced
- Printed circuit board
- Flame rectification probe
Related codes
305 Your boiler is temporarily pausing the hot water production to prevent itself from overheating or cycling on and off too frequently.
Your boiler is temporarily pausing the hot water production to prevent itself from overheating or cycling on and off too frequently.
What to check first
- Wait up to 15 minutes for the anti-cycle timer to expire
- Ensure hot water taps are fully closed
- Check that the hot water temperature setting on the control panel is not set excessively high
Related codes
Showing 11–20 of 32
306 Your boiler has detected that a flame is still present even though it has tried to turn the gas supply off, which indicates a potential safety control issue.
Your boiler has detected that a flame is still present even though it has tried to turn the gas supply off, which indicates a potential safety control issue.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
Related codes
306 V Your boiler has detected that a flame is still present briefly after the gas supply has been shut off.
Your boiler has detected that a flame is still present briefly after the gas supply has been shut off.
Parts commonly replaced
- Gas valve
- Main printed circuit board (PCB)
Related codes
815 Your boiler is struggling to accurately monitor the temperature of the water circulating through your heating system, which means it may not heat your radiators or hot water as efficiently as it should.
Your boiler is struggling to accurately monitor the temperature of the water circulating through your heating system, which means it may not heat your radiators or hot water as efficiently as it should.
Parts commonly replaced
- Low loss header temperature sensor
- Wiring harness
815 B Your boiler is not getting the correct temperature reading from an internal sensor connected to your heating system, so it has temporarily stopped working to protect itself.
Your boiler is not getting the correct temperature reading from an internal sensor connected to your heating system, so it has temporarily stopped working to protect itself.
Parts commonly replaced
- Low loss header temperature sensor
- Wiring harness
Related codes
1017 W Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low to operate safely.
Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low to operate safely.
What to check first
- Locate the external filling loop or internal key filling mechanism connected to your boiler.
- Open the valves slowly to let mains water into the system until the pressure gauge on the front panel reads between 1.0 and 1.5 bar.
- Close the valves tightly and press the reset button on your boiler if it does not restart automatically.
Parts commonly replaced
- Pressure relief valve
- Pressure sensor
- Automatic air vent
Related codes
1022 B Your boiler's hot water cylinder sensor has developed a fault, meaning it cannot accurately measure the temperature of your stored hot water.
Your boiler's hot water cylinder sensor has developed a fault, meaning it cannot accurately measure the temperature of your stored hot water.
Parts commonly replaced
- Hot water NTC sensor
- Cylinder sensor wiring harness
Related codes
1065 B Your boiler's internal water pressure sensor is faulty or disconnected, meaning the system cannot accurately read its water levels.
Your boiler's internal water pressure sensor is faulty or disconnected, meaning the system cannot accurately read its water levels.
Parts commonly replaced
- Water pressure sensor
- Pressure sensor wiring harness
Related codes
1068 W Your boiler's outdoor weather sensor has stopped working properly, meaning it can no longer automatically adjust your heating based on the outside temperature.
Your boiler's outdoor weather sensor has stopped working properly, meaning it can no longer automatically adjust your heating based on the outside temperature.
Parts commonly replaced
- Outside temperature sensor
- Wiring harness
Related codes
1075 W Your boiler has temporarily stopped working because a temperature sensor inside has detected an electrical fault.
Your boiler has temporarily stopped working because a temperature sensor inside has detected an electrical fault.
Parts commonly replaced
- Flow temperature sensor
- Wiring harness
Related codes
1076 W Your boiler has temporarily stopped working because it cannot read the temperature properly from its internal heating component.
Your boiler has temporarily stopped working because it cannot read the temperature properly from its internal heating component.
Parts commonly replaced
- Temperature sensor
- Wiring harness
Related codes
Showing 21–30 of 32
2920 V Your boiler has detected an issue with the flame and has shut down as a safety precaution to ensure no unburnt gas is escaping.
Your boiler has detected an issue with the flame and has shut down as a safety precaution to ensure no unburnt gas is escaping.
Parts commonly replaced
- Ionisation electrode
- Ignition lead
- Gas valve
Related codes
2927 B Your boiler has temporarily stopped working because the flame inside went out while it was trying to run.
Your boiler has temporarily stopped working because the flame inside went out while it was trying to run.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Sump seal
Related codes
2946 V Your boiler's computer brain has detected an internal electronic chip that doesn't match the model or has become loose.
Your boiler's computer brain has detected an internal electronic chip that doesn't match the model or has become loose.
Parts commonly replaced
- Code plug (HCM)
- Printed Circuit Board (PCB)
Related codes
2948 B Your boiler is struggling to stay lit when running at a low power level, which is preventing it from providing steady heating or hot water.
Your boiler is struggling to stay lit when running at a low power level, which is preventing it from providing steady heating or hot water.
Parts commonly replaced
- Ionisation electrode
- Gas valve
- Burner gasket
Related codes
2950 B Your boiler is trying to ignite but cannot detect a flame, meaning it is currently unable to provide heating or hot water for safety reasons.
Your boiler is trying to ignite but cannot detect a flame, meaning it is currently unable to provide heating or hot water for safety reasons.
Parts commonly replaced
- Ignition electrode
- Gas valve
- PCB
Related codes
2963 B Your boiler has detected that the temperature reading from its internal pipes is incorrect, so it has safely shut down to prevent potential overheating.
Your boiler has detected that the temperature reading from its internal pipes is incorrect, so it has safely shut down to prevent potential overheating.
Parts commonly replaced
- NTC temperature sensor harness
- Flow/Return temperature sensor
Related codes
2964 B Your boiler has detected that water is not flowing through its internal heating system quickly enough to operate safely.
Your boiler has detected that water is not flowing through its internal heating system quickly enough to operate safely.
Parts commonly replaced
- Plate-to-plate heat exchanger
- Diverter valve
- Central heating pump
Related codes
2965 B Your boiler has shut down because the water circulating inside it is getting much hotter than it should perfectly safely be.
Your boiler has shut down because the water circulating inside it is getting much hotter than it should perfectly safely be.
What to check first
- Check that all radiator valves are fully open to allow water to flow
- Ensure the system pressure gauge is between 1 and 1.5 bar
- Try resetting the boiler using the reset button on the control panel
Parts commonly replaced
- Circulation pump
- Flow temperature sensor (NTC thermistor)
- Main heat exchanger (flushing/cleaning)
Related codes
2966 B Your boiler is heating up too quickly because the water inside cannot flow away fast enough to cool the system down.
Your boiler is heating up too quickly because the water inside cannot flow away fast enough to cool the system down.
What to check first
- Check that all radiator valves are fully open
- Check that the boiler pressure gauge is between 1.0 and 1.5 bar
- Ensure there are no blockages in the magnetic system filter if one is fitted
- Reset the boiler after checking the above
Parts commonly replaced
- Central heating pump
- Main heat exchanger (flushing/cleaning)
- Flow/Return thermistors
Related codes
2967 B Your boiler has temporarily stopped because sensors inside are detecting an unusual difference in temperature across the main heating unit.
Your boiler has temporarily stopped because sensors inside are detecting an unusual difference in temperature across the main heating unit.
Parts commonly replaced
- Flow/Return temperature sensor
- Heat exchanger
Related codes
Showing 31–32 of 32
2970 B Your boiler has detected that the water pressure in your radiators is falling much faster than expected, which could indicate a significant leak.
Your boiler has detected that the water pressure in your radiators is falling much faster than expected, which could indicate a significant leak.
What to check first
- Check all visible radiator valves and pipework for signs of water leaking
- Top up the system pressure to between 1 and 1.5 bar using the internal filling link
- Restart the boiler to see if the code clears and the pressure remains stable
Parts commonly replaced
- Expansion Vessel
- Pressure Relief Valve
- Auto Air Vent
Related codes
2971 B Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
What to check first
- Locate the external filling loop or internal key under the boiler
- Slowly open the valve to let water into the system while watching the pressure gauge
- Close the valve tightly once the needle reaches the green zone, typically between 1.0 and 1.5 bar
Parts commonly replaced
- Filling loop
- Pressure relief valve
- Expansion vessel
Related codes
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