An F7 on a Worcester Greenstar means the boiler is picking up a flame signal when it shouldn’t, usually while it’s switched off or before the burner has started. We’re Clever Energy Boilers: Gas Safe registered (no. 554138), accredited Worcester Bosch installers based in Bingley, fitting boilers across Yorkshire, the North West and the Midlands. F7 only appears on older Greenstars, and an older Worcester showing it is usually better replaced with a new Worcester Bosch boiler for long-term efficiency and lower repair bills.
We’ve completed more than 25,000 installations in the last 15 years. Below you’ll find what Worcester’s manuals say F7 means, what causes it, the order an engineer works through to find the fault, and why there’s very little a homeowner can safely do about this one.
What does the Worcester F7 error code mean?
Worcester words F7 slightly differently from model to model, but it always points to a flame signal at the wrong time:
| Worcester model | What the manual says F7 means |
|---|---|
| ZWB and CDi models | Flame detected even though appliance switched off |
| Greenstar Highflow 440CDi | Flame detected after appliance shut off |
| Greenstar i | Ionisation detected before burner start |
| Greenstar Si and CDi Compact | False flame |
Ionisation is the flame signal the boiler reads through its electrode. So whichever wording your manual uses, the boiler thinks there’s a flame when there shouldn’t be one.
F7 is an older Greenstar code. Newer Worcesters, such as the Greenstar 2000, 4000 and 8000 ranges, use four-digit codes instead, and our Worcester boiler error codes guide lists those.
Why is my Worcester showing an F7 fault?
Worcester’s fault-finding points to four causes:
- The electrode assembly. It’s what senses the flame, and when it’s worn, contaminated or damaged it can give a false reading.
- Moisture on the PCB. Worcester’s fault-finding notes for F7 include “dry pcb”. A damp control board, often from a leak inside the boiler, can’t be trusted to read the flame signal. Our guide to why boilers leak covers where that water might come from.
- Flue gas recirculation or a blocked flue, where exhaust gets drawn back in and upsets combustion.
- A failed PCB. If the electrodes and flue check out, the board itself may have failed. Our boiler PCB faults guide explains more.
Is the Worcester F7 fault dangerous?
Treat it seriously. Your boiler relies on its flame sensing to run safely, and F7 means that sensing isn’t behaving as it should. That’s a job for an engineer, not a reason to keep pressing reset.
If you smell gas, open the windows, don’t use electrical switches, turn the gas off at the meter and call the National Gas Emergency Service on 0800 111 999.
What can I safely check at home when my Worcester shows F7?
There’s no DIY fix for F7. The safe steps stop at these:
- Reset once. On a Greenstar i, hold the reset button for about 5 seconds. On a CDi model, press reset for 3 seconds.
- Look at the flue from outside. Check nothing is blocking the terminal on the outside wall, but don’t touch it.
- Isolate the boiler if F7 returns. Switch it off at the fused spur and leave it off until a Gas Safe registered engineer has seen it.
If your home sits on an exposed hillside, as plenty do around Queensbury and Thornton, give the flue terminal a look after a storm. Don’t open the casing, and don’t try to dry or clean anything inside the boiler yourself.
When should I stop resetting the F7 error and get a Gas Safe engineer?
After one reset. If F7 comes back, the fault is still there, and Worcester’s manual sets out a clear order for finding it:
- Electrodes first. The engineer checks the electrode assembly for wear, contamination or damage and replaces it if needed.
- Combustion and flue next. A combustion (CO₂) check, plus an inspection of the flue for blockage or recirculation.
- PCB last. Dry the board if it’s damp, or replace it if it has failed.
Water near the PCB matters because the board is what reads the flame signal. If it’s damp, that reading can’t be relied on, which is why drying the board is part of Worcester’s fault-finding. Whatever leak caused the damp needs fixing as well.
Why does the Worcester F7 fault code keep coming back?
A reset doesn’t touch the cause. A worn electrode keeps wearing, a slow leak keeps dripping near the board, and a flue that recirculates will do it again whenever the conditions line up.
Is an F7 error a sign you need a new Worcester Bosch boiler?
Often, yes. F7 shows up on Greenstar CDi Classic, Si and i models, and most of those are now 10 to 20 years old. Fixing wear on the combustion side, and possibly replacing the PCB too, is poor value on a boiler that age.
Typical UK prices, as a guide only:
| Repair | Typical UK cost |
|---|---|
| Electrode or ignition parts | £120 to £250 |
| PCB (control board) | £250 to £500 |
A combustion check and any flue repair come on top. Replacement makes more sense if:
- Your Worcester is more than 8 years old and losing efficiency
- F7 came back after an electrode change
- The engineer found a leak as well as a PCB problem
- Other fault codes have appeared in the last year
Our guide on how to know when your boiler needs replacing covers the other signs, and how much a new boiler costs shows what to budget.
Get a new Worcester Bosch boiler with Clever Energy
We fit Worcester Bosch boilers in Bingley, Keighley, Skipton, Bradford, Leeds and across Yorkshire, plus the North West and the Midlands. As accredited Worcester Bosch installers we’ll swap your old Greenstar for a modern Worcester sized for your home, with a long, market-leading warranty available through us. Read more about our Worcester Bosch boiler installation service, get a fixed online price for a new boiler today, or request a callback. If you’d rather talk it through, call 0330 055 2210 between 8am and 8pm on weekdays or 10am to 4pm at weekends.
Worcester F7 fault code FAQs
What does F7 mean on a Worcester boiler?
A flame signal at the wrong time. The boiler has detected a flame while it’s switched off or before the burner starts, and the exact wording runs from “false flame” to “ionisation detected before burner start”.
Is a Worcester F7 fault dangerous?
Treat it as serious, because the flame sensing isn’t working as it should. Reset once, and if F7 returns, isolate the boiler and get a Gas Safe registered engineer. If you smell gas, call 0800 111 999.
Can water leaking onto the PCB cause a Worcester F7 error?
Yes. Moisture on the PCB is one of the listed causes, and drying the board is part of Worcester’s fault-finding. The leak needs fixing too, or the code will come back.
What’s the difference between Worcester F7 and FA error codes?
They’re close relatives. FA is shown when a flame is still sensed after the gas valve has closed, while F7 is how older models report a flame when the appliance is off or before the burner starts.
Can I reset a Worcester F7 fault?
Yes, once. Hold reset for about 5 seconds on a Greenstar i, or press it for 3 seconds on a CDi. If F7 comes back, isolate the boiler and get an engineer.
More Worcester Bosch error codes
F7 belongs with the false-flame codes. Before this one, have a look at the Worcester Bosch 228 fault code, where the boiler senses a flame when nothing is burning; after it, the Worcester Bosch FA fault code covers a flame sensed after the gas valve closes. The full list sits on our Worcester boiler error codes guide.