Worcester Bosch boiler fault codes: what each one means
Current Worcester Bosch Greenstar boilers show a fault as a number on the display: the 2000 beside an H symbol, the 4000 and 8000 as a coded text message. The older Greenstar Ri has no display and flashes its blue light instead. The tables below give each code's meaning and Worcester's stated action, from its own manuals.
Reviewed by Jordan Valentine-Dunn, Gas Safe registered engineer · Portsmouth Gas Heating · Last reviewed September 2026
Start with Worcester's own figure: its user instructions say no appliance fault is found on over 30% of service calls. Check power, timer, gas and a cold system pressure of 1 to 1.5 bar before treating a code as a boiler fault.
Where does a Worcester Bosch boiler show its fault code?
| Range | How the fault shows | Reset, in Worcester's words |
|---|---|---|
| Greenstar 2000 | An H symbol with the code. A locking fault flashes with the H. | Press the up and down arrows together until H and ! disappear, or switch off and on. |
| Greenstar 4000 | A text message with the code and an icon coloured by severity. | Press the two arrow keys until Reset is displayed. |
| Greenstar 8000 Life and Style | A message on the display with the code. | Press the two arrow keys together until the fault disappears. |
| Greenstar Ri | No display: the blue mains light flashes. | Turn the heating knob anticlockwise to RESET, hold about five seconds, turn it back. |
What do the letters O, B, V and W mean?
They are Worcester's fault categories. O is an operating code, not a fault. B is a blocking fault: the boiler stops and restarts by itself once the cause clears. V is a locking fault: it stays off until reset. W is a maintenance code. Worcester adds that a blocking fault that persists becomes a locking fault.
What do the Greenstar 2000 fault codes mean?
| Code | Meaning (Worcester's words) | Manufacturer's stated action |
|---|---|---|
| 2971 (B) | System pressure too low | Top up to the pre-set pressure and vent; check the pressure sensor harness and voltage. |
| 227 (B/V) | No flame signal after ignition | Check gas supply and inlet pressure, gas valve, air intake, a blocked or frozen condensate trap or pipe, flue, burner, electrodes. |
| 229 (B) | Flame failed during burner operation | Check gas working pressure, the gas-air ratio and the ionisation electrode; on LPG, gas in the tank. |
| 224 (B/V) | Safety temp. limiter has tripped | Check the limiter and harness, flow temperature, system pressure, trapped air, the pump and any blockage. |
| 281 (B) | Pump pressure increase too low | Check flow pressure and circulation, the pump's tacho or PWM plug and cable; replace the pump. |
| 2910 (V) | Error in the flue gas system | Check the flue gas system, mount the flue pipe correctly, remove any obstruction. |
What do the Greenstar 4000 fault codes mean?
| Code | Meaning (Worcester's words) | Manufacturer's stated action |
|---|---|---|
| 1017 (W) | System pressure too low | Top up and vent; check the voltage to the pressure sensor and its signal; replace the sensor. |
| 2971 (B) | System pressure too low | Triggered between 0.6 and 0.3 bar. Top up; with the intelligent filling loop, use Start filling in the main menu. |
| 227 (V) | No flame signal after ignition | Check gas supply and valve, air intake, a blocked siphon or frozen condensate pipe, flue, heat exchanger, burner, electrodes. |
| 2927 (B) | Flame failed during burner operation | Check the gas valves are open, supply pressure, flame sense electrode, CO2 at minimum and maximum, flue and combustion air. |
| 281 (B) | Pump stuck or running in air | Check system pressure, vent the system and pump, check circulation and the pump's wiring. |
| 2910 (V) | Fault in flue system | Remove any flue obstruction, carry out the flue integrity test, check the sump and siphon. |
On a 4000 system boiler, use the system manual 6720891162: it prints different descriptions against 2927 and 281.
What do the Greenstar 8000 Life and Style fault codes mean?
| Code | Meaning (Worcester's words) | Manufacturer's stated action |
|---|---|---|
| 1017 (W) | System pressure too low | Top up and vent; check the voltage to the pressure sensor and its signal; replace the sensor. |
| 2971 (B) | System pressure too low | Top up to the pre-set pressure, comparing it with the internal pressure dial; check the pressure sensor. |
| 227 (V) | No flame signal after ignition | Check gas supply and valve, air intake, a blocked or frozen condensate trap or pipe, flue, heat exchanger, burner, electrodes. |
| 224 (V) | Maximal flue gas thermostat or heat exchanger maximal thermostat has activated | Check the limiter and harness, flow temperature, system pressure, trapped air, the pump and any restriction. |
| 2910 (V) | Fault in flue system | Remove any flue obstruction, carry out the flue integrity test, check the sump and siphon. |
What does the flashing blue light on a Greenstar Ri mean?
| Blue light | Meaning (Worcester's words) | Manufacturer's stated action |
|---|---|---|
| No light | No power at control board | Check mains supply, mains switch, fuses F1 and F2, transformer; otherwise replace the board. |
| Slow flash, mostly off | Ignition lockout | Check gas pressure, the gas valve, CO2, the flue, a blocked or frozen condensate pipe, ignition electrodes. |
| Slow flash, mostly on | Flue overheat, heat exchanger overheat, or flue pressure switch | Check the baffles are fitted, water pressure, venting, the pump, safety thermostats, and the flue for blockage. |
| Fast flash | Volatile lockout (sensor, fan or code plug) | Check sensors and leads (8k to 20k ohms), 230V at the fan, and that the code plug is seated. |
How do you read a code on the job? Two examples
A Greenstar 4000 shows 1017 with the gauge at 0.6 bar cold. It is a W code, so the boiler is warning rather than locking out: Worcester says top up and vent, then check the pressure sensor's voltage and signal.
A Greenstar 2000 shows 227 with a flashing H on a frosty morning. Worcester's list for 227 includes a frozen condensate pipe, and its user instructions say to thaw only a pipe at ground level, never at height, and never with boiling water.
When should you stop resetting and call an engineer?
When the same code returns after a reset. Worcester asks for the displayed code, appliance type, serial number and commissioning date. The 2000 and 4000 manuals also describe 2981, a super lock-out, which needs the underlying fault found before its double reset.
A fault code is the manufacturer's diagnostic starting point, not a repair. Only a Gas Safe registered engineer may open the appliance: regulation 3 of the Gas Safety (Installation and Use) Regulations 1998 limits gas work to an HSE-approved class of persons. If you smell gas, reset nothing and call the National Gas Emergency Service on 0800 111 999.
For engineers, Manifold's fault codes library records every code seen on your team's checks against the appliance, so a repeat visit starts with last time's fault, and its manuals lookup finds Worcester's documentation by GC number.
Read next
Frequently asked
Sources
- Worcester Bosch, Greenstar 2000 installation and maintenance instructions (6721839340)
- Worcester Bosch, Greenstar 2000 user instructions (6721820553)
- Worcester Bosch, Greenstar 4000 combi installation manual (6720891161)
- Worcester Bosch, Greenstar 4000 system installation manual (6720891162)
- Worcester Bosch, Greenstar 4000 user instructions (6720891170)
- Worcester Bosch, Greenstar 8000 Life combi installation manual (6720883865)
- Worcester Bosch, Greenstar 8000 Life combi user instructions (6720883872)
- Worcester Bosch, Greenstar 8000 Style combi installation manual (6720883864)
- Worcester Bosch, Greenstar Ri ErP installation, commissioning and servicing instructions (6720813283)
- Worcester Bosch, Greenstar Ri ErP user instructions (6720813340)
- Legislation.gov.uk, Gas Safety (Installation and Use) Regulations 1998, regulation 3
- National Gas, emergency contacts
Related guides
Last reviewed September 2026. This guide is general information, not legal or safety advice, gas safety work must be carried out by an appropriately Gas Safe registered engineer. Rules can change, so check the linked official sources for the current position.