Boiler
290.C
Error code 290.C on a Worcester Bosch boiler points to a fault with the appliance’s fan or air pressure monitoring system — specifically, a problem the boiler has detected with flue gas extraction or airflow. It can range from a minor, easily resolved issue to a fault that genuinely requires a Gas Safe registered engineer, so it’s important to know the difference. In this guide, you’ll learn exactly what 290.C means, what’s most likely causing it on your Worcester Bosch boiler, what you can safely check yourself, and when it’s time to pick up the phone.
What does this error mean?
The 290.C error code on Worcester Bosch boilers — including popular models in the Greenstar range (such as the 8000, 4000, CDi, and Si series) — is a fault code related to the fan speed or air pressure circuit. More specifically, it indicates that the boiler’s control board has detected that the fan is not running at the correct speed, or that the air pressure switch (also called the flue gas pressure switch or differential pressure switch) is not responding as expected during the startup or operating sequence. In plain English: your boiler has a fan that pushes exhaust gases safely out through the flue and draws fresh air in for combustion. If that fan isn’t spinning fast enough, spinning too fast, or if the boiler can’t confirm airflow is correct via its pressure switch, it shuts itself down and displays 290.C as a safety measure. This is a protective lockout — the boiler is doing its job by refusing to fire until it knows combustion gases can be safely expelled. Do not attempt to override this lockout.
Est. repair cost
£150–£500 total for a professional repair (fan replacement or pressure switch), or £300–£600+ if the PCB requires replacement. Parts alone: fan £150–£300, pressure switch £20–£60, PCB £200–£400.
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Do NOT attempt a DIY repair on internal boiler components. Because this fault relates directly to safe flue gas extraction, working inside your boiler on the fan, pressure switch, or wiring is not legal or safe for an unqualified person. Gas appliances must be serviced and repaired by a Gas Safe registered engineer. The steps below are limited to safe external checks you can do before calling a professional.
Step 2 — Perform a boiler reset. On most Worcester Bosch Greenstar models, press and hold the reset button (usually marked with a flame and a line through it, or labelled ‘Reset’) for 3–5 seconds until the display changes. Allow the boiler 2–3 minutes to attempt a restart. If it fires up successfully and the error does not return within 24 hours, the fault may have been a temporary glitch. If it locks out again, move to the next steps.
Step 3 — Check your external flue terminal. Go outside and locate the flue outlet on your external wall (it’s typically a white or grey circular vent, often near the boiler on an outside wall). Check visually that it is not blocked by leaves, a bird’s nest, spiderwebs, or — in winter — ice. Do not poke anything into the flue. If you can see an obvious external blockage and safely remove it without touching the flue pipe itself (e.g. clearing debris from directly in front of the terminal), do so.
Step 4 — Check for bird guards or flue covers. Some flue terminals have mesh guards that can become clogged over time. If you can see the mesh is heavily blocked with debris, note this to report to your engineer — do not attempt to dismantle or modify the flue terminal yourself.
Step 5 — Check the boiler’s condensate pipe (if applicable). If your boiler is a condensing model (most modern Worcester Bosch boilers are), check that the white plastic condensate pipe — which usually exits through an outside wall or discharges into a drain — has not frozen solid in cold weather. A frozen condensate pipe causes a separate error (EA229) but can occasionally be associated with pressure-related faults. If the pipe feels solid with ice, you can apply warm (not boiling) water to the external section to thaw it, or wrap it in a warm cloth.
Step 6 — Turn off and fully power-cycle the boiler. Switch the boiler off at the programmer or thermostat, then turn it off at the fused spur switch on the wall (the red-switched socket near the boiler). Wait 5 full minutes, then restore power and attempt a restart. This allows the PCB to fully reset and can clear spurious 290.C faults caused by voltage fluctuations.
Step 7 — Check your boiler’s service history. If your Worcester Bosch boiler has not been serviced in the last 12 months, a blocked heat exchanger, dirty burner, or worn fan can all contribute to this fault. An annual service by a Gas Safe engineer is the best preventative measure and is often required to maintain your warranty.
Step 8 — If the error persists after a reset and the above checks, stop here and call a Gas Safe registered engineer. Do not continue to reset the boiler repeatedly (more than 2–3 times) as this can mask a genuine safety issue. The fault requires professional diagnosis with appropriate tools.
📞 When to call a professional
You should call a Gas Safe registered engineer if: the error code 290.C returns after one or two resets; you can see no obvious external flue blockage; or the boiler makes unusual noises (grinding, humming, or a fan that sounds slower or louder than usual) before locking out. Because 290.C relates directly to safe combustion gas extraction, this is not a fault to live with or repeatedly reset in the hope it goes away. When you call, tell the engineer: the exact error code displayed (290.C), the model of your Worcester Bosch boiler (printed on the label inside the front panel or in your manual), how long the fault has been occurring, how many times you have reset it, and any observations about fan noise or flue blockage. This will help them diagnose the fault faster and arrive with the right parts. You can verify an engineer is Gas Safe registered at GasSafeRegister.co.uk or by asking to see their Gas Safe ID card.
⚖️ Repair or replace?
Worcester Bosch is one of the most popular boiler brands in the UK, and parts availability is generally very good — even for boilers 10–15 years old. The most common repairs for a 290.C fault are a replacement fan (typically £150–£300 for the part alone, depending on the Greenstar model) or a replacement air pressure switch (typically £20–£60 for the part). If the PCB is at fault, expect to pay £200–£400 for the part. Labour typically adds £80–£150 per hour depending on your region, with most 290.C repairs completing in 1–2 hours. As a rule of thumb: if your boiler is under 8 years old and has been regularly serviced, repair is almost always the right call — Worcester Bosch boilers are well-built and have a good service life of 15+ years with proper maintenance. If your boiler is over 12–15 years old and this is not its first fault, it is worth getting a quote for a new boiler alongside the repair. A new Worcester Bosch Greenstar boiler costs approximately £1,500–£3,000 fully installed, depending on the model and property. Worcester Bosch boilers also come with manufacturer warranties of up to 12 years if installed by an Accredited Installer, which could affect your decision if the boiler is still within that period — check your paperwork before authorising any repair.