Steady or flashing: what the blue light is telling you
A flashing blue light on a Worcester boiler is a fault signal, while a steady blue light simply means the boiler is being asked to heat. That is how Worcester Bosch describes it in the Greenstar i user instructions, both for the 25i and 30i ErP combi (document 6 720 806 946) and for the Greenstar i System ErP range from 9i to 24i (document 6 720 806 947). On page 7 of both, the light is called the heat demand and fault indicator: it comes on during a heating or hot water demand and "flashes during a fault condition".
A blue glow while the radiators warm up is normal. A pulsing light, usually with a code on the display, is not.
Not every Worcester has this light. The user instructions for the Greenstar 4000 (document 6 720 891 170) and the Greenstar 8000 Life combi (document 6720883872) make no mention of a blue light. The only light they describe belongs to the optional Key accessory, which shows red, yellow or green. A coloured light flashing on a 4000 or 8000 is the Key, not the boiler.
| Model range | Blue light? | What to look at instead |
|---|---|---|
| Greenstar i combi (25i, 30i ErP) | Yes. Steady for demand, flashing for a fault | The code on the text display |
| Greenstar i System (9i to 24i ErP) | Yes. Can be switched off for demand but still flashes for faults | The code on the text display |
| Greenstar 4000 | Not described in the user instructions | Fault message with a coloured icon, top right of the display |
| Greenstar 8000 Life | Not described in the user instructions | Status code and diagnostic code on the display |
| Key accessory (4000 and 8000) | No. Red, yellow or green LED | Flashing red means a fault such as lost communication with the boiler |
On the Greenstar i System, section 3.4.6 of the user instructions explains that the blue light can be turned off for normal heat demand. Even then, it will still flash to warn you of a fault. If your light never comes on during heating, your installer may have switched that function off.
Reading the code that appears with the light
The blue light only tells you that something is wrong. The display tells you what. On a Greenstar i, the alert shows as a short letter code and a number, and the user instructions give "EA and 227" and "224 Temp" as examples. Write down exactly what you see before you touch anything.
EA 227 is the code most people see. The Greenstar i user instructions link EA to no gas supply or low gas pressure, a blocked condensate outlet or a blocked flue. Our page on Worcester EA 227 goes through that fault in detail, and the Worcester Bosch error codes hub lists the other codes we cover, such as the low pressure code CE 207 and the overheat code E9 224. If the display shows a flashing letter rather than a code, check our guide to Worcester boiler display symbols, because a flashing A (air purge) or T (component test) is a mode, not a fault.
Common reasons the light starts flashing
Most flashing lights trace back to a short list of causes, some of which you can check from outside the boiler.
No gas reaching the boiler
If the burner cannot light, the boiler locks out. See whether your gas hob lights. On a prepayment meter, check there is credit and that the meter has not tripped. Look under the boiler at the gas isolation valve: the handle should sit in line with the pipe. If you smell gas at any point, stop, turn the supply off at the meter if it is safe to, open windows and call the National Gas Emergency Service on 0800 111 999.
Low water pressure
The Greenstar i user instructions ask you to recharge the system if the gauge reads below 1 bar, filling to between 1 and 1.5 bar using the filling link under the boiler.
Frozen or blocked condensate pipe
A blocked condensate outlet is one of the EA causes Worcester lists. In a frost, the plastic pipe running outside can freeze and back water up into the boiler. Thaw it with warm (never boiling) water or a hot water bottle along its length, then reset.
A flue problem
A blocked flue is also on Worcester's list. From the ground, you can check that the outside terminal is not covered by snow, a bush or a bird's nest. Anything beyond that, including any work on the flue itself, is for a Gas Safe registered engineer.
A test or service mode left on
The Greenstar i display shows a chimney sweep symbol when an engineer has set the boiler to maximum or minimum output during a service. If you see that symbol after a visit, ask the engineer to return the boiler to normal operation rather than trying to clear it yourself.
How to reset the boiler safely
On a Greenstar i, Worcester's instruction is to press the reset button "briefly once". The display shows Reset while the boiler restarts.
- Note the code and check the gas, pressure and condensate pipe first.
- Press reset once, briefly.
- Wait a few minutes for the boiler to restart.
- If the code returns, look again at the likely cause and try a second time.
- After two or three failed attempts, stop and call for help.
The Greenstar i user instructions also warn that some codes cannot be cleared by a simple reset because of the boiler's internal safety systems. On the 4000 and 8000 ranges the reset uses two keys on the display rather than a button, and our Worcester boiler reset guide shows the method for each model.
When the light keeps flashing, or comes on but nothing happens
If you reset and the light carries on flashing with the same code, the reset has failed and the cause is still there. Worcester's instructions say exactly this: an unsuccessful reset brings the code back and the blue light continues to flash.
A steady blue light with cold radiators is a different problem. The boiler is seeing a demand, so the thermostat and timer are working, but the heat is not getting where it should. Check that the pressure is in range and that radiator valves are open.
No blue light at all can also mean something. The Greenstar i user instructions list a momentary power failure as a cause, and the remedy is to disconnect the boiler's supply, wait a few seconds and reconnect it, which you can do at the fused spur. If the display is blank too, check the fuse in the spur and your consumer unit.
When to call a Gas Safe registered engineer
Call an engineer if the light is still flashing after two or three resets, if the code is one that will not clear, if lockouts keep returning even though the boiler runs for a while in between, or if you suspect a flue issue. If your boiler is still within its Worcester guarantee, contact Worcester Bosch first, because repairs by an unapproved engineer may affect that cover.
Never remove the front casing to find out why the light is flashing. The gas valve, burner, electrodes and fan are inside and must only be worked on by a Gas Safe registered engineer.
Tell the engineer your model, the exact code and what you have already checked. Typical UK prices for the repairs most often behind a flashing light:
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £60 to £150 |
| Ignition electrode | Typically £90 to £180 |
| Condensate pipe reroute or insulate | Typically £80 to £200 |
| Flue repair or adjustment | Typically £150 to £400 |
| Gas valve replacement | Typically £180 to £350 |