Worcester boiler flashing blue light: what it means and what to do

Steady blue, flashing blue and no light at all

Worcester fits a blue mains indicator to most of its Greenstar boilers. In the user instructions for the Greenstar 24i and 28i Junior, for example, it is labelled as the power on and fault indicator. What it is doing tells you a lot before you touch anything.

Boilers with a digital display will usually show a fault code alongside the flashing light, such as EA with a cause number, E9 or A1. Write the whole code down, including any number that appears after the letters. That code is far more useful to an engineer than the light on its own.

First, is there any smell of gas?

If you can smell gas, do not reset the boiler or operate any electrical switches. Turn off the gas at the meter if it is safe to do so, open the windows and call the National Gas Emergency Service on 0800 111 999. A flashing light is a fault signal; a gas smell is an emergency, and it comes first.

Checks to make before you press reset

A lockout is the boiler protecting itself. Resetting it without looking for the reason often just brings the light back a few minutes later. These checks take a couple of minutes and clear a good share of callouts on their own.

• Gas supply: is the hob or any other gas appliance working? If you are on a prepayment meter, check it has credit. Make sure the gas isolation valve under the boiler has not been turned off.
• Boiler pressure: look at the gauge on the front. Worcester's guidance is around 1 bar with the heating off, rising to about 1.5 bar or a bit more when it is running. Below 1 bar, the system needs topping up.
• Condensate pipe: in freezing weather, check the plastic pipe that runs from the boiler to an outside drain. If it is frozen, the boiler shuts down and the reset light flashes.
• Power: if the blue light went off during a power cut, switch the boiler off at its master switch, wait a few seconds and switch it back on.
• Controls: check the programmer, room thermostat and any smart control are actually asking for heat, and that the time is correct after a power cut.

How to reset a Worcester boiler with a flashing blue light

On Greenstar models with a reset button, press and hold it for about five seconds. When the reset works, the reset button stops being lit and the blue indicator stops flashing. After a frozen condensate pipe has been thawed, Worcester's instructions say to reset and then wait two to three minutes for the boiler to restart.

Reset once, after you have made the checks above. If the blue light starts flashing again straight away, or after the boiler has run for a short time, stop there. Repeated resets can mask the cause and, on some faults, make it worse. Our guides on how to reset a boiler and a boiler lockout that keeps returning explain why.

Never remove the boiler casing or try to adjust anything inside it. Work on a gas appliance must be carried out by a Gas Safe registered engineer.

The usual causes of a flashing blue light

The light itself does not say what went wrong. These are the causes engineers most often find behind it.

• Ignition or flame failure: the boiler tried to light but could not detect a flame, or lost it while running. On models with a display this often shows as EA, commonly with 227 or 229 after it. Gas supply problems, a worn ignition or sensing electrode, or a fault with the gas valve are typical reasons.
• Frozen or blocked condensate pipe: water from the boiler cannot drain away, so it shuts down. This is very common in cold snaps where the pipe runs outside.
• Low water pressure: the system has lost water, often through a small leak, a weeping pressure relief valve or after radiators have been bled.
• Overheating or poor circulation: a stuck pump, sludge or closed valves stop the heat being carried away, and the boiler locks out to protect itself.
• Flue, fan or sensor faults: less common, and only something an engineer can test.

If your boiler has a frozen condensate pipe

Worcester's user instructions are clear about what a householder can and cannot do here. Only thaw a pipe that is at ground level and easy to reach. Never climb a ladder to a pipe at height. Warm the frozen section with a hot water bottle, a microwaveable heat pack or a cloth soaked in warm water, or pour warm water over it from a watering can. Do not use boiling water, which can damage the pipe.

Once the pipe has thawed, reset the boiler and give it two to three minutes. If it freezes again every cold night, the pipe needs rerouting, insulating or upsizing. Our guide to a frozen condensate pipe covers the longer-term fixes.

When to call an engineer

Call if the blue light is still flashing after one reset, if the same code keeps coming back, if the pressure keeps dropping, if water is leaking from the boiler, or if the boiler is making loud banging or boiling noises. The same applies if you have no heating or hot water and there are elderly people, young children or anyone unwell in the house.

Loyal Plumbers has 10 vans covering London and everywhere inside the M25, 24 hours a day, and our gas work is carried out by Gas Safe registered engineers. When you call, tell us the boiler model (it is printed on the front or under the fascia), any code on the display, what the pressure gauge reads, how many times you have reset it and whether the weather is freezing. Our call-out charge is £60, and the engineer explains what they have found and what the repair involves before any work starts.