Worcester's own list of display symbols
Worcester boiler display symbols fall into two groups: status icons that tell you what the boiler is doing, and alerts that need action. Worcester Bosch's support page "What do the error symbols mean on my boiler?" is not tied to one model (it mentions the New Greenstar 24/28 and CDi Conventional boilers), but it covers the symbols owners ask about most. We have summarised each one below with what Worcester says to do.
| Symbol | What it means | What to do |
|---|---|---|
| Siphon fill mode | Low burn for about 15 minutes to fill the condensate trap, after the boiler has been off for a day or so or the control knob has been turned down and up | Wait. Call if it lasts over half an hour |
| Key lock | Front panel locked (New Greenstar 24/28 only) | Unlock as your user instructions describe |
| One key or two keys pressed | The panel has registered a key press | Nothing |
| Maximum mode | Running at full output; should not last more than 15 minutes | Call if still showing after 15 minutes |
| Minimum mode | Running at lowest output; same 15 minute limit | Call if still showing after 15 minutes |
| Set range (service function 1A) | Operating within a set range | Contact Worcester's technical department |
| Air purge | Burner off, pump pulsing, about 15 minutes | Wait. Call if it lasts over half an hour |
| Save | A menu setting has just been saved | Nothing |
| Temperature blocking (gradient limitation) | Flow temperature rising too fast; burner stops for two minutes and restarts | Call if it keeps happening |
| Service due | Alternates with the flow temperature; a service is due | Book a service |
| Heating pump blocked | Alternates with the flow temperature | Arrange an engineer visit |
| SE code | Not a fault; shown after 2,324 running hours, roughly a year of use | Book a service |
Our separate guide to Worcester air purge mode explains why that symbol can seem to come back after a power cut.
Greenstar i symbols and letters
The Greenstar i ErP user instructions (document 6 720 806 946, pages 9 and 10) list the symbols on the text display of the 25i and 30i combi. They include hot water, central heating, chimney sweep, alert, service mode, burner on and a confirmation symbol. Two letters also appear on this display:
- Flashing T: the boiler is in component test mode, which an engineer uses.
- Flashing A: the boiler is in air purge mode.
The chimney sweep symbol shows during a service when the boiler has been set to maximum or minimum output. The burner on symbol means the flame is alight. The Greenstar i also has a blue light, steady for a heat demand and flashing for a fault, which our guide to the Worcester flashing blue light covers in full.
Greenstar 4000, 8000 Life and 8000+ icons
The newer ranges have a larger display and navigation keys, and their icons are mostly about what is switched on.
Greenstar 4000
The Greenstar 4000 user instructions (document 6 720 891 170) say the burner display lights when the burner is alight, and the heating symbol showing or not showing tells you whether heating is on or off. Faults appear as a message with an icon in the top right corner, whose colour reflects how serious the fault is, along with a numbered code. The reset is done with the keys until Reset appears on the screen.
Greenstar 8000 Life
Table 3 of the 8000 Life combi user instructions (document 6720883872) lists central heating on, hot water on, burner on or off, a fault symbol shown with a status code and diagnostic code, Wi-Fi connection (with the accessory), RF connection (with the Key accessory), Eco mode, chimney sweep mode and service mode. At very low pressure the display alternates LoPr with the pressure reading.
Greenstar 8000+ and 8000+ Style
The 8000+ user instructions (document 6721890748) add symbols for hot water off, central heating off and a holiday symbol to the familiar heating, hot water and burner icons.
Flashing versus steady symbols
A steady symbol usually describes a normal state: heating on, burner lit, Eco mode active. Flashing or alternating normally means a temporary mode or a message that wants your attention.
- A flashing A or T on a Greenstar i is a mode (air purge or component test), not a fault.
- The service due and pump blocked symbols alternate with the flow temperature rather than replacing it.
- On the Key accessory for the 4000 and 8000, flashing red means a fault such as no communication, flashing yellow means please wait, flashing green means start-up is running and constant green means everything is normal.
Locking and blocking faults
Worcester faults behave in one of two ways. A blocking fault stops the boiler for as long as a condition lasts and then clears by itself. Temperature blocking is a good example: the burner pauses for two minutes and restarts. A low pressure condition also blocks the boiler until the pressure is restored, which is fixed by topping up to 1 to 1.5 bar.
A locking fault keeps the boiler off until someone presses reset. Ignition and flame faults such as EA 227 work this way. The Greenstar i user instructions warn that some codes cannot be cleared by a simple reset because of the boiler's internal safety systems, and those need Worcester or an engineer.
If a locking fault relates to ignition, flame or the flue, reset once only. If it returns, call a Gas Safe registered engineer. Never open the casing to investigate.
Faults that may not show a code
Some problems never reach the display. A boiler that has lost power shows nothing at all, and the Greenstar i user instructions list a momentary power failure as a reason the blue light goes out. Heating that does not respond can be a programmer, thermostat or battery issue rather than a boiler fault. A Key LED that is off can simply mean power-saving mode. Check the fused spur, the controls and the pressure before assuming the boiler has failed. For the codes that do appear, our Worcester Bosch error codes hub links to each one.
What to do for each symbol, and when to call an engineer
Status icons and the save symbol need nothing from you. Siphon fill and air purge need patience, up to half an hour. Service due and SE mean book an annual service, which typically costs £80 to £150. Pump blocked, temperature blocking that keeps repeating, and any alert that comes back after two or three resets need a Gas Safe registered engineer.
Maximum mode, minimum mode, set range and chimney sweep are installer test functions. Do not try to enter them, and if one is still showing after a service visit or after 15 minutes, call the engineer back rather than pressing keys to clear it.