Worcester Bosch Greenstar 4000 Fault Codes
The Worcester Bosch Greenstar 4000 is the mid-range combi and system boiler that replaced the long-running Greenstar i in 2020 — one of the biggest-selling boilers in the UK ever since. It shares the modern Bosch control platform with the flagship 8000, which means it also shares its fault-code language: a short primary code, usually followed by a three-digit sub-code that pins the cause down. For owners that is good news — the 4000's codes are unusually specific for a mid-market boiler. An "EA 227" is not just "ignition problem" but specifically no flame detected after ignition attempts, and the sub-codes distinguish sensor faults, fan faults and flue problems that older boilers lumped together. This page explains how the 4000 reports and resets faults, and highlights the codes owners meet most often, each linking to its full diagnosis page.
Where Greenstar 4000 fault codes appear
The 4000 has a simple digital display behind the bottom flap of the fascia showing the current temperature in normal running and the fault code when something trips. Codes appear as a letter-number pair (EA, C7, E9…) usually followed by a numeric sub-code — note both parts exactly. A spanner or warning symbol alongside indicates a fault requiring attention rather than a temporary status.
Resetting a Worcester Bosch Greenstar 4000
Hold the reset button below the display for a few seconds; the boiler will clear the lockout and retry. For low-pressure faults, re-pressurise to 1–1.5 bar via the filling loop first — the pressure reading shows on the display. One reset is diagnostic; repeated resets against a returning code are not, and on ignition faults they simply repeat failed gas admissions.
Common Greenstar 4000 problems
The 4000's common complaints mirror the platform: EA-family ignition lockouts (very often a frozen condensate pipe in winter, or gas supply interruptions), low system pressure, and C-series fan/flue codes. The condensate trap and siphon are also known service points on this platform — a gurgling boiler that locks out on EA in cold weather is the condensate story almost every time.
Most common Greenstar 4000 fault codes
- EA EA on a Worcester Bosch boiler is an ignition lockout: the boiler tried to light its… Read more →
- EA 229 The EA 229 fault code means your Worcester Bosch boiler established a flame successfully… Read more →
- C6 The C6 fault code appears on Worcester Bosch boilers when the control system detects that… Read more →
- C7 The C7 fault code appears when the boiler's fan fails to reach the correct operating… Read more →
- E9 The E9 fault code means the safety temperature limiter on your central heating flow… Read more →
- F7 The F7 fault code means your Worcester Bosch boiler's ionisation circuit has detected a… Read more →
- A1 The A1 fault code on a Worcester Bosch boiler indicates that the circulation pump is not… Read more →
- D1 The D1 fault code appears when your Worcester Bosch boiler is unhappy with the reading… Read more →