Worcester Boiler Flashing Blue Light: What It Means

A flashing blue light on a Worcester Bosch boiler usually means it has detected a fault and shut itself down. On Greenstar models with a blue mains indicator, the light stays on steadily while the boiler is powered and working, and flashes when it locks out. Worcester's Greenstar i Junior instructions describe exactly this: in a fault, the reset button flashes once a second and the blue mains light flashes, and you reset it by holding the reset button for around five seconds. Before you do, check the pressure gauge and, if it is freezing outside, the condensate pipe. If the light comes back after one reset, leave it and book a Gas Safe engineer.

What the flashing blue light means

Worcester has made several generations of Greenstar boiler and the control panels differ, so start by reading the model name on the front of the case or on the data label. On the older i Junior, Si and similar ranges, there is a blue power or mains indicator and a separate reset button. Newer ranges such as the Greenstar 4000 and 8000 use a digital display with symbols and codes instead. The principle is the same: a steady indicator is normal, and a flashing one is the boiler telling you it has stopped for a reason.

The flashing light does not tell you what the fault is. On models with a display, a code will usually appear at the same time. Write it down, or take a photo, before pressing anything. The code is the most useful piece of information you can give an engineer, and it can disappear once the boiler is reset. Our guide to boiler error codes explains why codes need checking against the exact model rather than a generic list. If the display shows EA 227, see our guide to the Worcester EA 227 fault code.

Checks before you reset

1. Look at the pressure gauge

Low pressure is one of the most common reasons a sealed system boiler stops. Worcester's manual says the system needs re-charging if the gauge reads less than 1 bar, and to fill it to between 1 and 1.5 bar. If yours is below 1 bar, top it up using the filling link or loop, following our step-by-step guide to repressurising a boiler. If the gauge is very high instead, see our guide to boiler pressure that is too high.

2. Check the condensate pipe in cold weather

Condensing boilers drain acidic water through a plastic condensate pipe, which often runs outside to a drain. Worcester's manual is specific: a frozen condensate pipe will make the boiler shut down and show a flashing reset light. If it has been below freezing and the pipe runs outside, that is the likely cause. The manual advises thawing it with a hot water bottle, a heat pack or warm water poured over the pipe, only at ground level where it is easy to reach, and never with boiling water. Our guide to a frozen or blocked boiler flue and condensate pipe covers this in more detail.

3. Check gas and power

If other gas appliances such as the hob are not working either, or your prepayment meter has run out, the boiler cannot light. Check the fused spur switch next to the boiler is on. If you smell gas at any point, do not reset anything. Open windows, avoid switches and call the National Gas Emergency Service on 0800 111 999.

4. Rule out a simple controls issue

Make sure the timer or programmer is calling for heat and the room thermostat is turned up. This will not cause a flashing fault light on its own, but it is worth checking before you assume the reset has failed.

How to reset a Worcester boiler

For the Greenstar i Junior, Worcester's instructions are straightforward. Press and hold the reset button for approximately five seconds. When the boiler resets, the reset button stops being lit and the mains indicator stops flashing. After thawing a condensate pipe, the manual says to press reset for five seconds and then wait two to three minutes for the boiler to restart.

Other Greenstar models may have the reset on a different button or in a menu. Use your own model's user manual, which Worcester publishes online. Do not remove the boiler casing to look for a reset. Anything inside the case is for a Gas Safe registered engineer.

If the light keeps flashing

One reset after checking the basics is reasonable. If the blue light starts flashing again, the fault is still there and the reset is only restarting the same failure. Worcester's own advice on its broken-boiler page is that you should never try to fix a broken boiler yourself, because it could be dangerous and could invalidate your guarantee.

Faults that commonly cause repeated lockouts include ignition problems where the boiler tries to light but does not detect a flame, overheating, a blocked internal condensate trap, fan or sensor faults and pressure that keeps falling because of a leak or a failed expansion vessel. Each needs testing, not guessing. If your boiler has also been cutting out without a flashing light, our guide on a boiler that keeps turning off covers the overlap.

If the boiler is less than a couple of years old or still under a Worcester guarantee, contact Worcester or your installer first, because work by another engineer during the guarantee period may affect it. Keep your service record handy either way.

Booking a repair

When you call, give the engineer:

• The exact model, for example Greenstar 30i or Greenstar 4000.
• Any code shown on the display, and how often the fault happens.
• The pressure reading when cold.
• Whether you have hot water, heating, both or neither.
• When the boiler was last serviced.

That lets the engineer arrive with a likely diagnosis and, often, the right parts. We confirm the price before any work starts, so you know what you are agreeing to. If there is no flashing light but the taps run cold, see our guide to a Worcester boiler with no hot water.

Frequently Asked Questions