What F7 228 means
An F7 228 code means your Greenstar saw signs of a flame at a moment when there should not be one. The boiler has refused to continue and needs resetting.
A condensing boiler proves its flame by ionisation. A small current passes through the flame to the flame sensing electrode, and the control box reads that current as proof the burner is alight. Before each start, the gas valve is closed and the burner is cold, so the reading should be zero. If the board sees current at that stage, it has a false flame signal. A boiler that cannot trust its flame sensing cannot tell whether it has lit safely, so it locks out.
Worcester's installation, commissioning and servicing instructions for the Greenstar 9i to 24i System ErP (document 6 720 806 945) describe cause 228 as "Ionisation current detected before burner-start". The instructions for the Greenstar 27i and 30i System Compact (document 6 720 807 726) list F7 228 as a "Flame error" in the locking fault table, with the remedy column reading "False flame. Flame detected before burner start." Those manuals are printed in columns that copy unevenly online, so the remedy is listed alongside the code rather than in a cleanly aligned row.
F7 228, F7 328 and the 8000 Life version
The digits after F7 matter, because the Compact manual gives F7 two cause codes.
| Code | Models | Worcester wording | What it points to |
|---|---|---|---|
| F7 228 | Greenstar i System ErP and System Compact | "Ionisation current detected before burner-start" / "Flame error" | The flame sensing circuit |
| F7 328 | Greenstar i System Compact | "Internal error" | The electronics or the mains supply |
| 228 | Greenstar 8000 Life combi | "Flame signal without flame present" | Flame sense lead, earth tags, sump |
For cause 328, the System ErP manual adds that the mains voltage or frequency may be inconsistent, and its suggested action is to check the voltage and frequency. That is a very different job from a false flame, so give the engineer the full code.
What causes a false flame signal
The flame sensing electrode or its lead
Worcester's Greenstar 8000 Life installation and maintenance instructions (document 6720883865) start with this for cause 228: check the flame sense and the lead, and replace them if required. A damaged lead or a deteriorated electrode can feed the board a reading it should not see.
Earth connections
The 8000 Life guidance also points engineers to the earth tags. The ionisation signal depends on a sound earth path back to the control box, so a loose or corroded earth can upset what the board measures.
Moisture in the sump
The sump is mentioned in the 8000 Life checks too. Elsewhere in the Compact manual, Worcester links moisture in the sump to a blocked sump or condensate trap, which is why a condensate problem is worth ruling out when F7 appears in cold weather.
Internal or supply faults (F7 328 only)
If your display shows F7 328 rather than F7 228, the flame circuit is not the first suspect. An inconsistent mains supply or an internal fault in the electronics is what the manuals describe.
Safe checks you can make
- Write down the whole code. F7 228 and F7 328 send the engineer to different parts of the boiler.
- Reset once, then watch. On the Greenstar i System models, press the reset button on the fascia. Stop after two or three attempts. Our guide to resetting a Worcester boiler covers the different control panels.
- Check the condensate pipe in a freeze. If the plastic pipe outside is frozen, thaw it with warm (not boiling) water or a hot water bottle, then reset. Our frozen condensate pipe guide shows how to find it.
- Look under the boiler. Without opening anything, check for drips or damp, since moisture inside the boiler is one of the things the engineer will look for.
- Note the timing. Record whether F7 appears on the first start of the day, after a long period off, or at random. For F7 328, also note any flickering lights or power cuts.
Do not take the casing off or touch the electrode, its lead, the earth tags or the gas valve. A boiler with an unreliable flame signal should not be forced to run with repeated resets. If you smell gas, turn the boiler off and call the National Gas Emergency Service on 0800 111 999.
What the engineer will check
A Gas Safe registered engineer will confirm the cause code, then inspect the flame sensing electrode and its lead, the earth tags and the sump and condensate trap. For F7 328 they will check the incoming voltage and frequency first. After any work around the burner, expect them to check combustion with a flue gas analyser before leaving.
It helps to tell them the full code, your exact model, how many resets you tried, and whether the fault followed cold weather, a power cut or recent work on the boiler. If the boiler also shows EA 227 at times, mention it, because that code is the opposite problem: no flame detected after ignition.
Typical repair costs in the UK
Prices depend on the model, the region and what the engineer finds. These are typical ranges, not quotes.
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £60 to £150 |
| Flame sense electrode replacement | Typically £90 to £180 |
| Flame sense lead replacement | Typically £100 to £200 |
| Earth connection or wiring repair | Typically £100 to £180 |
| Condensate pipe reroute or insulation | Typically £80 to £200 |
An annual service, typically £80 to £150, gives an engineer the chance to look at the electrode and clean the condensate trap before either causes a lockout. You can find other Greenstar codes on our Worcester Bosch fault code page.