Worcester Bosch Error Codes: Full List and What They Mean

How Worcester Bosch error codes work

Worcester Bosch is one of the UK's most common boiler brands, and most modern Greenstar combi, system and heat-only models show a fault as a short code on the front display. Older units flash a number or letter; newer ones with a text display (and the EasyControl app) often spell out the issue too.

The codes usually come as a letter category followed by a number — for example EA, E9 or C6. The letter hints at the type of fault (an "E" or "EA" group around ignition and flame, a "C" group around the fan and air, an "A" group around water flow and sensors).

The exact code, and especially the suffix digits, can vary between models and generations, so always cross-check against the manual or the sticker inside your boiler's casing flap for your specific unit.

How Worcester Bosch codes are structured

Worcester Bosch doesn't use one flat list — it uses five kinds of code, and knowing which one you're looking at saves a lot of guessing. The single most useful trick is the cause code: pressing the return/back button reveals a three-digit number that pinpoints the actual fault behind a more general lockout.

So when you read a Worcester code, note the letter-group and press the return/back button to read the cause number — quoting both (for example "EA 227") lets an engineer come prepared with the right part.

Common Worcester Bosch Greenstar error codes

The tables below are grouped by model range, because the same letter group can carry a different cause number on different boilers.

Each lists the code with the cause suffix you'll actually see, a plain-English meaning, and whether it's something a homeowner can safely act on or a job for a Gas Safe registered engineer. Treat the detail as general guidance, not a diagnosis — your manual is the final word for your model.

Where two boilers share a code we've noted it; if your suffix differs, trust your manual over the table.

Greenstar i / Si Compact and CDi Compact

The newer combi ranges most homes now have. Press the return/back button to read the cause number.

Greenstar i (Greenstar 25i/30i/old "i" range)

Greenstar CDi Classic (Regular & Combi) and CDi Highflow

The longer-serving CDi range, including the Highflow models. Older CDi units may show a fault as a flashing symbol rather than a neat alphanumeric code.

Greenstar 8000 & Greenstar 4000

The current Greenstar 8000 (Life/Style) and 4000 ranges share the same letter-plus-cause-number system as the Compact range above — for example CE 207 (low pressure), EA 227 (flame fault) and the C6 fan codes carry across. The 4000 uses a simplified set of the same codes.

Because firmware and cause numbers were refreshed on these models, read the cause code via the return button and check it against the manual supplied with your specific 8000/4000 unit rather than assuming an older suffix.

If your code isn't in these tables, don't guess from a similar-looking one. The same two characters can mean different things across the Greenstar i, CDi and Compact ranges — the cause number is what tells them apart. Check your model's manual or the Worcester Bosch support pages for the exact meaning.

Which faults can a homeowner safely deal with?

Only a short list of these is genuinely DIY. Everything that touches the gas valve, the burner, the flame-sensing electrode, the flue or the sealed combustion circuit means taking the casing off and using test equipment — that is Gas Safe engineer work only, and it is illegal as well as dangerous for an unregistered person to attempt it.

Here's the quick split at a glance:

Even on the "safe" side, the rule is one reset only: if the same code returns, stop and book an engineer.

The homeowner-safe checks are:

• Low pressure — top up using the filling loop (steps below).
• A single front-panel reset — for a lockout such as EA, reset once and watch what happens.
• A frozen condensate pipe in cold weather (typically shows as EA 229) — thaw the external plastic pipe with warm (not boiling) water. (A D5 code can also point to a frozen pipe, but more often means a condensate-pump or drainage fault that needs an engineer.)
• Power and controls — check the boiler has power, the fused spur is on, and the thermostat or programmer is calling for heat.

The reset-once rule

For a lockout code like EA, you can press and hold the reset button on the front panel for a few seconds to restart the ignition sequence. Do this only once.

How to repressurise a Worcester Bosch boiler

If you have a low-pressure code, repressurising via the filling loop is a safe homeowner job. The gauge should read about 1 to 1.5 bar when cold, rising towards roughly 2 bar when hot. Below about 1 bar is low.

1. Turn the boiler off and let it cool for a few minutes.
2. Find the filling loop — on many Greenstar models this is an internal keyed valve underneath the boiler; on others it's a silver braided hose with a tap at each end.
3. Open the valve(s) slowly. You'll hear water flowing in.
4. Watch the gauge and stop at about 1.0–1.5 bar. Don't go past ~2 bar.
5. Close the valve(s) firmly, switch the boiler back on, and reset once if the code is still showing.

If the pressure keeps falling over days or weeks, you have a leak or an expansion-vessel fault that needs an engineer — not endless topping up. For more detail, see our guide to low boiler pressure.

Frozen condensate pipe (typically EA 229)

In a cold snap, one of the most common Worcester lockouts is a frozen condensate pipe. The boiler can't drain the small amount of acidic water it produces, so it shuts down — typically showing EA 229 (loss of flame signal during the burn).

A D5 code can also be caused by a frozen pipe, though it more usually points to a condensate-pump or drainage fault. It often strikes overnight after the first hard frost.

This one is a safe homeowner job:

1. Find the condensate pipe — usually a white or grey plastic pipe running out through an external wall to a drain.
2. Pour warm (not boiling) water along it, concentrating on any bends, the open end, or the lowest external point where ice forms. Boiling water can crack the pipe or the fittings.
3. Once the ice clears, reset the boiler once and it should fire normally.

H-codes and service symbols (not always a fault)

Not every symbol on the display is a lockout. Worcester also shows advisory and "normal operation" indicators, so before you panic about a fault, check whether what you're seeing is actually one of these:

• H-codes (e.g. H07) — maintenance codes. The boiler usually keeps running, but something needs attention soon. H07 indicates low water pressure with performance limited — repressurising clears it.
• Spanner / "SE" service-due symbol — not a fault. Worcester displays it once the boiler has run for around 2,324 hours (roughly a year), prompting an annual service. The display may flash between the spanner and the flow temperature.
• Siphon-fill (an alternating bar symbol) — normal. The boiler runs at low burn for about 15 minutes to fill the condensate trap, often after it has been off for a day or the controls were turned down and back up. Let it finish.
• Air-purge — normal at first start-up after installation: the boiler won't fire but pulses the pump on and off to clear air.
• Key / child lock — the front panel has been locked (on the newer Greenstar 24/28). Unlock it via the panel rather than treating it as a fault.

If any of these persist far longer than expected, treat it like a fault and call an engineer. Anything beginning with an F, EA, E9 or a flashing triangle is a genuine lockout, not a service prompt.

What a Worcester Bosch repair typically costs

If a code returns after a single reset, you'll need a professional repair. These are indicative 2026 ranges and vary by region, parts and call-out timing.

This is where a policy earns its keep. With boiler cover, a repair like a failed fan or gas valve is handled for the price of your monthly premium instead of a one-off bill.

If you're weighing it up, our guides to the best boiler cover and whether boiler cover is worth it break down what's actually included — and you can compare cover across our panel in a couple of minutes.

Frequently asked questions