BoilerFaultCodes 8C
Super-Lock caused by too frequent thermostat overheat detections during burning
Worcester Bosch Greenstar 25Si Compact ErP Fault codes & diagnostics
52 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Natural GasLPG 25-30 kW 2005-2019 Discontinued
GC Numbers 47-406-7447-406-73
Replaced by: Greenstar 4000
Download the Worcester Bosch Greenstar 25Si Compact ErP manual
PDF
Versions & GC numbers
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. 1 Emergency
7 High
1 Medium
43 Unrated
Which version do you have?
The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.
| GC number | Appliance (register name) | Produced |
|---|---|---|
| 47-406-74 | Greenstar 25Si Compact ErP LPG | 2015–present |
| 47-406-73 | Greenstar 25Si Compact ErP | 2015–present |
Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.
Just want the most common Worcester Bosch Greenstar 25Si Compact ErP faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 52 documented codes
Tap any card for details
8E
Reset to factory settings (displayed with the spanner symbol)
9A
HCM (Heat Control Module)
9U
HCM problem
212
Safety or flow temperature rises too fast
213
Temperature difference between supply and return exceeding limit
229
Loss of flame signal during operation
234
Gas valve error
241
Return sensor disconnected
260
No temperature rise after burner starts
Showing 11–20 of 52
261
Ignition timing error
276
Flow temperature exceeds 95°C
277
Safety temperature exceeds 95°C
278
Sensor test failed
280
Recycle time error
285
Return temperature exceeds 95°C
328
Internal error
338
Too many short burner starts without confirmation
380
Inlet DHW temperature higher than the DHW outlet temperature
A1
Pump stuck or running in air
Showing 21–30 of 52
A3
Flue gas sensor shorted
A7 Your boiler's temperature sensor for hot water has stopped working properly, meaning your taps may only provide cold or lukewarm water.
Your boiler's temperature sensor for hot water has stopped working properly, meaning your taps may only provide cold or lukewarm water.
Parts commonly replaced
- Hot water NTC sensor
- Connecting lead/wiring
Related codes
A8 Your boiler has lost its connection to your thermostat or remote heating controller, meaning it cannot receive instructions to turn the heating on.
Your boiler has lost its connection to your thermostat or remote heating controller, meaning it cannot receive instructions to turn the heating on.
What to check first
- Check and replace the batteries in your room thermostat or remote control unit.
- Ensure the heating controller is within range of the boiler and has not been moved.
- Turn the power switch to the boiler off and back on again to restart the radio connection.
Parts commonly replaced
- Batteries
- RF receiver
- Room thermostat / Sense control
Related codes
b7
Internal error - replace control board
C1
Airflow stopped during operation
C4
Airflow present during last 24 hours
C6 Your boiler’s internal fan is not spinning fast enough to safely clear away exhaust fumes, which has caused the system to shut down for safety.
Your boiler’s internal fan is not spinning fast enough to safely clear away exhaust fumes, which has caused the system to shut down for safety.
Parts commonly replaced
- Fan Assembly
- Main PCB
- Air Pressure Switch
C7
Fan not running
CC
Outdoor sensor defect
CE
No pressure variation detected after switching pump
Showing 31–40 of 52
CF
Water pressure sensor not connected or short-circuit
D1
Return temperature too high
D3
external cut-off switch activated
D4
Temperature difference between flow and safety sensor exceeding limit
E2 Your boiler has detected a faulty internal temperature sensor, which means it cannot accurately monitor the water temperature and has shut down as a safety precaution.
Your boiler has detected a faulty internal temperature sensor, which means it cannot accurately monitor the water temperature and has shut down as a safety precaution.
Parts commonly replaced
- CH Flow NTC Sensor
- Connecting Wiring Harness
Related codes
E3
Return temperature higher than supply temperature (some time after burner start)
E4
Preheat sensor on DHW inlet Short Circuit
E5
Flow temperature too high
E9 Your boiler has shut down because it has detected that the water inside is Getting too hot, which is a safety feature to prevent damage.
Your boiler has shut down because it has detected that the water inside is Getting too hot, which is a safety feature to prevent damage.
What to check first
- Check if any radiator valves are closed and open them fully
- Ensure your system pressure is between 1 and 1.5 bar on the gauge
- Press the 'Reset' button for five seconds to restart the boiler
Parts commonly replaced
- Overheat Thermostat
- Circulation Pump
- Main Heat Exchanger (Flushing)
Related codes
EA Your boiler is failing to light the gas or stay lit, which has caused it to shut down for safety.
Your boiler is failing to light the gas or stay lit, which has caused it to shut down for safety.
What to check first
- Check if other gas appliances like your cooker are working to ensure gas is being supplied to the house.
- If it is freezing outside, check if your white plastic condensate pipe is frozen and thaw it with warm water.
- Press and hold the 'Reset' button for five seconds to see if the system restarts.
Parts commonly replaced
- Ignition Electrode
- Flame Sensing Electrode
- Gas Valve
- Printed Circuit Board (PCB)
Showing 41–50 of 52
EC
Flue gas temperature rising too fast
ED
CH: flue gas temperature rising but supply temp. not
EE
HW: supply temperature too hot
EF
Supply and/or return temperatures do not change after burner start
F0 Your boiler's internal computer has encountered a critical electronic software or hardware error that is preventing it from running safely.
Your boiler's internal computer has encountered a critical electronic software or hardware error that is preventing it from running safely.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Wiring harness
Related codes
F7 Your boiler thinks it can see a flame inside the system even though it should be turned off, which is a safety conflict that prevents it from starting up.
Your boiler thinks it can see a flame inside the system even though it should be turned off, which is a safety conflict that prevents it from starting up.
Parts commonly replaced
- Flame sensing electrode
- Ionisation lead
- Control board (PCB)
Related codes
FA Your boiler is still detecting a flame even though it has tried to shut off the gas, which is a safety conflict causing the system to lock out.
Your boiler is still detecting a flame even though it has tried to shut off the gas, which is a safety conflict causing the system to lock out.
Parts commonly replaced
- Gas Valve
- Ionisation Lead
- Control Board (PCB)
Related codes
Fb
Gas valve EV1 leak test failed
FD
Mains power error - electrical power interruption
H5
No feedback from pump
Showing 51–52 of 52
H11
Hot water outlet sensor defect, hot water can still be delivered but with less control (sensor open/short circuit or out of position)
H13
A time has been set in the Service interval function i.e. 1 to 72 months and that time has expired. Menu 2.5F allows this feature to be set (1 to 72), a 0 will disable this function.