Worcester Bosch EA fault code: what it means and what to check
EA means the boiler tried to light and could not confirm a flame, so it locked out. The three causes the manufacturer lists, what you can safely check yourself, and where it becomes an engineer's job.
16 August 2026 · 6 min read
If your Worcester Bosch Greenstar is showing EA with the blue light flashing, the boiler has tried to start, opened the gas valve, and then failed to confirm that a flame was actually alight within its safety window. So it has shut itself down and locked out.
That is the boiler working correctly, not failing. A boiler that opened the gas valve and could not prove there was a flame has to stop, because the alternative is unburnt gas going somewhere it should not. Understanding that is useful, because it tells you the fault is upstream of the burner: something to do with getting gas in, getting the products of combustion out, or the boiler's ability to sense the flame.
There is usually a three digit number underneath the EA on the display. Write it down. Worcester ask you to quote both when you call them, and it narrows the diagnosis considerably.
What causes it, in the order it usually turns out to be
Worcester's own user instructions list three causes for EA, and in our experience they come up in roughly this order once you account for the time of year.
- A blocked or frozen condensate pipe. Overwhelmingly the most common cause in cold weather, and the one most likely to be fixable without an engineer. A gurgling noise from the boiler is the classic tell.
- A gas supply problem. No gas at all, or gas pressure that has dropped too low. If it is a prepayment meter that has run out, or the whole street has an issue, this is not a boiler fault at all.
- A blocked or damaged flue. Less common, but it does happen: nests, debris, or a terminal that has been rendered over or obstructed.
- Beyond that list, and firmly in engineer territory: a dirty or failed ionisation electrode, a faulty gas valve, or a control board that is no longer reading the flame signal correctly.
What you can safely check yourself
None of this involves opening the boiler or touching anything on the gas side. If a check requires the case off, it is not on this list.
- Is there gas elsewhere in the house? If you have a gas hob, does it light normally? If it does not, the problem is the supply, not the boiler.
- Prepayment meter in credit? Obvious, and it catches people out more often than you would think.
- Listen to the boiler when it tries to fire. A gurgling or bubbling sound points hard at the condensate.
- Follow the small plastic pipe that leaves the bottom of the boiler and goes outside. If it runs up an external wall or into a drain outdoors and the weather has been cold, feel it for ice.
- If it is frozen and you can reach it safely from the ground, warm water poured slowly along the pipe will usually clear it. Not boiling water, and not on a ladder.
- Look at the flue terminal outside. Snow, a bird's nest, a bin bag, ivy, anything obstructing it.
- Then press the reset button once. Once, not repeatedly.
Where it stops being your job
Press reset once and give the boiler a couple of minutes. If it fires and stays running, the underlying cause was almost certainly the condensate, and it will come back next cold snap unless the pipe run gets sorted properly.
If it locks out again on EA, stop. Do not keep resetting it. Each reset asks the boiler to open the gas valve again, and repeatedly forcing a start on an appliance that cannot prove it has lit is exactly the situation the lockout exists to prevent.
Do not remove the boiler case. Worcester's instructions are unambiguous that only a competent engineer can remove the case and carry out work under the Gas Safety (Installation and Use) Regulations, and doing it yourself will invalidate the guarantee as well as being unsafe. Anything involving the gas valve, the burner, the electrode or the flue is a Gas Safe registered engineer's job, full stop.
And if you smell gas at any point, do not touch the boiler at all. Turn the gas off at the meter, open windows, get out, and call the National Gas Emergency Service on 0800 111 999 from outside.
Source: Gas Safe Register
What an engineer will actually do
Worth knowing, because it lets you judge whether the quote you get is sensible or whether someone is guessing.
A competent engineer diagnosing EA will check the gas working pressure at the appliance under load, not just the standing pressure, because a supply that looks fine at rest can collapse when the boiler asks for full rate. They will read the ionisation current the boiler is measuring, which is available in the appliance's own information menu and tells you directly whether the flame is being sensed. They will inspect the electrode for cracking, carbon build-up and gap, check the condensate trap and its route outside, and verify the flue.
The cost of the repair is driven mostly by which of those turns out to be the answer, and how much of the boiler has to come apart to reach it. An electrode is a small, routine consumable part. A gas valve or a control board is a much bigger item and a longer visit. Any quote given over the phone before someone has read the ionisation current and tested the gas pressure is a guess, and you should treat it as one.
It is also worth knowing that Worcester state no appliance fault is found on over 30% of all their service calls. A good proportion of EA callouts turn out to be a frozen pipe or an empty meter, which is precisely why the safe checks above are worth ten minutes of your time first.
Is EA a repair or a replace signal?
On its own, no. EA is not a terminal diagnosis and plenty of boilers throw it once, get a new electrode, and run for years.
The question changes with age and with which part failed. An electrode or a condensate route problem on a boiler that is otherwise healthy is straightforward maintenance. A gas valve or a control board on a boiler that is already past its guarantee, that has thrown other codes recently, or where parts are getting harder to source is the point where you should at least price the alternative before committing to the repair.
The honest test is not the age of the boiler on its own. It is whether this is the first significant thing to go wrong or the third.
Why we see so much of this locally
Around Northampton and Milton Keynes a very large share of the housing stock is estate build from the last forty years, and on those houses the boiler is frequently in a kitchen on an outside wall, in a utility, or in a garage. All three tend to mean an external condensate run, and an external condensate run is the thing that freezes.
Worcester's own installation guidance is specific about what makes those runs survive cold weather: keep the external pipework as short as possible, maintain a fall of at least 2.5 degrees over horizontal sections, and minimise bends and connectors. A pipe with a long horizontal section, a couple of unnecessary elbows and no insulation will freeze in the first proper cold snap of every winter, and each time it does you get another EA.
So if this is the second or third winter running that your boiler has locked out in the cold, the fault is not really the boiler. Ask an engineer to look at the condensate route itself rather than just thawing it again.
The short version
EA means no flame was confirmed and the boiler locked itself out on purpose. Check for gas elsewhere in the house, listen for gurgling, feel the outside condensate pipe for ice, look at the flue terminal, then reset once. If it locks out again, that is where a homeowner's part of this ends.
Have the three digit number under the EA ready when you call, and have the boiler's model and serial number to hand from the sticker behind the front panel flap. It saves a lot of time.
If the boiler is old enough that you are weighing a repair against replacing it, we can arrange quotes from Gas Safe registered installers covering Northampton and Milton Keynes so you can see both numbers before you decide.