Worcester Bosch boiler error codes
11 codes that Worcester Bosch publishes for its boilers, each with what it means, the likely cause, what you can safely check and when to call a Gas Safe registered engineer. Tap your code:
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone. Anything else is for a Gas Safe registered engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999. Codes that need one are marked Gas Safe engineer.
Read this first
Worcester Bosch Greenstar boilers show a two-character code on the display, while the reset button and the blue fault indicator flash. This page is the full error-code table of the Greenstar CDi Classic combi user instructions (2014), eleven codes. The same instructions say not to try to rectify any of these faults yourself and to contact a competent, qualified engineer (Gas Safe registered personnel), with one exception spelled out: for EA, if it is safe to do so, check the gas, a frozen condensate pipe and the flue outlet. Newer Greenstar models (the 8000 range, for example) show three- or four-digit numbers and a text message instead; those are not these codes.
EA Flame not detected
- What it means
- The boiler tried to light but did not detect a flame.
- Likely cause
- Worcester’s fault-finding table: no gas supply or low gas pressure, a blocked condensate outlet (ice or something stuck in it), or a blocked flue.
- What you can safely check
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.
- If it is safe to do so, check the gas is on in the house. No gas or low pressure: contact your gas supplier.
- Check the condensate pipe outlet for a blockage such as ice. To thaw a frozen pipe at ground level, apply a hot water bottle, heat pack or warm cloth, or pour warm — never boiling — water on it; never try one that is at height. Then hold reset for five seconds and wait two to three minutes.
- If it is safe to do so, check the flue outlet outside for damage or a blockage.
- Otherwise press the reset button for three seconds.
- When to call a Gas Safe registered engineer
- If EA comes back or the boiler will not restart, call Worcester or another Gas Safe registered engineer.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
A7 Hot water sensor faulty
- What it means
- The hot water temperature sensor (NTC) is faulty.
- Likely cause
- A failed sensor or its connection.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
A8 Controls not communicating
- What it means
- Communication with the FX controls has broken.
- Likely cause
- A break in the link between the boiler and its FX controls.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
b1 Code plug not detected
- What it means
- The boiler cannot find its code plug, the part that tells the electronics which model it is.
- Likely cause
- A missing or faulty code plug.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
C6 Fan too slow
- What it means
- The fan speed is too low.
- Likely cause
- A fan fault.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
E2 Heating flow sensor faulty
- What it means
- The central heating flow temperature sensor (NTC) is faulty.
- Likely cause
- A failed sensor or its connection.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
E9 Overheat cut-out tripped
- What it means
- The safety temperature limiter in the central heating flow has tripped.
- Likely cause
- The water in the heating flow got too hot.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
F0 Internal error
- What it means
- An internal error in the boiler.
- Likely cause
- Not stated beyond “internal error”.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
F7 Flame seen while switched off
- What it means
- A flame is detected even though the boiler is switched off.
- Likely cause
- A fault in flame sensing or the gas valve.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
FA Flame seen after gas shut off
- What it means
- A flame is detected after the gas was shut off.
- Likely cause
- A fault in flame sensing or the gas valve.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call Worcester or another Gas Safe registered engineer. The user instructions say not to try to put right any fault in this table yourself.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
Fd Reset pressed by mistake
- What it means
- The reset button was pressed when there was no fault to reset.
- Likely cause
- A press of the reset button by mistake.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer The table still says not to rectify it yourself: if Fd stays on the display, call Worcester or another Gas Safe registered engineer.
Source: Worcester Bosch, Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
A code that is not listed here
Worcester’s newer Greenstar 8000 user instructions show a numbered fault code (for example 232) with a text message and name only one code, 2980, which needs a qualified heating engineer immediately. For any other number, use your own model’s instructions or call Worcester with the code and the boiler’s data.
We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.
Related pages
Source
Every code on this page comes from these pages, published by Worcester Bosch and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.
- Worcester Bosch: Greenstar CDi Classic combi user instructions (6 720 812 179, 2014/07): 4.2 fault finding, 4.3 error codes Checked 2026-09-28.
- Worcester Bosch: Greenstar 8000+ combi user instructions (6721890748, 2024/06): 9 troubleshooting Checked 2026-09-28.