Boiler
F.29
The F.29 error code on a Worcester Bosch boiler indicates an ignition failure — the boiler has tried to light but failed to detect a flame. This is a moderately serious fault that will leave you without heating or hot water until it’s resolved.
What does this error mean?
Worcester Bosch boilers use a flame sensor (ionisation electrode) to confirm that the burner has successfully ignited. When the boiler attempts to fire up and cannot detect a stable flame within a set number of tries, it locks out and displays F.29 as a safety measure. This lockout prevents unburned gas from accumulating inside the appliance — so it’s a feature, not just a fault.
Est. repair cost
£100–£250 for a Gas Safe engineer call-out plus parts (electrode, sensor, or gas valve replacement)
🔍 Likely causes
🛠️ Step-by-step fix
Check your gas supply first: make sure other gas appliances in your home (hob, gas fire) are working. If they’re not, contact your gas supplier — this is a supply issue, not a boiler fault.
Reset the boiler: press and hold the reset button (usually marked with a flame or ‘R’ symbol) for 3–5 seconds until the display changes. Allow the boiler 2–3 minutes to attempt a full restart.
Check the condensate pipe in cold weather: if temperatures are below freezing, locate the white plastic condensate pipe that exits the boiler to an outside drain. If it’s frozen solid, thaw it carefully with warm (not boiling) water and then reset the boiler.
Check the boiler pressure: a pressure reading below 1 bar on the front gauge can cause ignition problems. Refer to your boiler manual to repressurise to 1–1.5 bar using the filling loop — this is safe for a homeowner to do.
If the fault returns after one or two resets, stop here. Repeated lockouts mean the root cause has not been fixed, and continuing to reset without a repair risks further damage. Call a Gas Safe registered engineer.
📞 When to call a professional
If the boiler locks out again within 24 hours of a reset, or if you cannot identify a simple cause such as a frozen condensate pipe or low pressure, you need a Gas Safe registered engineer. Tell them the exact error code (F.29) and how many times the boiler has locked out — this helps them diagnose faster. Never attempt to open the boiler casing, adjust the gas valve, or clean internal components yourself: this is illegal without Gas Safe registration and genuinely dangerous.
⚖️ Repair or replace?
A Gas Safe engineer call-out in the UK typically costs £80–£120, with parts such as an ignition electrode (£20–£50) or flame sensor (£30–£60) adding to the total. If your Worcester Bosch boiler is under 10 years old and was well-maintained, repair is almost always the right call — Worcester Bosch parts are widely available and engineers know these boilers well. If your boiler is over 12–15 years old and facing its second or third significant repair, replacement with a new A-rated boiler (typically £1,800–£3,000 installed) is likely more cost-effective in the long run.