Biasi E24 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E24 fault code mean?
The E24 code on a Biasi boiler has two distinct meanings depending on which model range you own. On newer Biasi models (such as the Rinnova), E24 signals a probable flue or chimney obstruction — the control board has detected that combustion gases are not being safely expelled and has locked the boiler out as a precaution. On older Biasi models (such as the Riva and 24S ranges), E24 indicates incorrect burner operation during ignition — the burner failed to establish properly when the boiler attempted to fire. In both cases the boiler will not operate until the underlying fault is resolved. Check your model handbook if you are unsure which definition applies; the troubleshooting approach overlaps significantly either way.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Blocked or obstructed external flue terminal Common
Debris such as leaves, a bird's nest, or accumulated dirt around the flue outlet on the outside wall can restrict airflow enough to trigger E24 on newer models. In winter, a partial covering of snow or ice can have the same effect. The boiler locks out because it cannot safely vent combustion gases.
- Faulty or failing flue fan Common
The fan is responsible for drawing combustion gases out through the flue. If it has seized, is running below speed, or has a failing motor, the boiler cannot confirm safe ventilation and will lock out. This is one of the more frequent mechanical reasons for E24 on both newer and older Biasi ranges.
- Defective air pressure switch (APS) Common
The air pressure switch monitors the fan's performance by detecting the pressure differential it creates. A faulty or sticking APS may report that the fan is not working even when it is, causing a spurious E24 lockout. Equally, a genuine low-pressure reading from a partially working fan will trigger the same code.
- Insufficient or interrupted gas supply Common
On older Biasi models where E24 relates to ignition failure, low mains gas pressure or a closed/partially closed gas isolation valve can prevent the burner from lighting correctly. A temporary interruption from the supplier can also cause a one-off appearance of this code.
- Dirty or blocked burner and ignition components Sometimes
A build-up of carbon deposits on the burner jets or electrodes can prevent reliable ignition. A contaminated ionisation sensor may also fail to confirm a flame is present, causing the boiler to lock out after ignition attempts.
- Unstable power supply or electrical fault Sometimes
Electronic control boards are sensitive to voltage fluctuations and poor connections. A loose plug, a voltage surge, or a deteriorating connection at the boiler's supply can cause erratic behaviour that manifests as an E24 code, particularly on older models.
- Faulty PCB (printed circuit board) Rare
If the control board itself is malfunctioning it may generate fault codes incorrectly or fail to sequence ignition properly. PCB failure is relatively uncommon but should be considered if all other components have been checked and found to be in order.
How to fix it
- Reset the boiler once or twice DIY safe
Locate the reset button on the boiler's front panel and hold it for approximately 5–10 seconds until the display changes or the boiler restarts. Allow up to 10 minutes for the full ignition sequence to complete. Do not attempt more than two resets in succession — repeated failed ignition attempts can allow gas to accumulate in the combustion chamber, which is dangerous.
- Inspect the external flue terminal for obstructions DIY safe
Go outside and visually inspect the flue outlet on the external wall. Look for bird nests, leaves, debris, or any physical blockage around the terminal. If you can safely reach it at ground level or from a safe step, gently clear away any loose material. Do not use ladders in unsafe conditions and do not attempt to dismantle or modify the flue.
- Confirm the gas supply is turned on DIY safe
Check that the gas isolation valve on the pipe leading to the boiler is in the open (inline) position. Also check that other gas appliances in the property — such as a hob or gas fire — are working normally. If no gas appliances are working, there may be a supply interruption; contact your gas supplier.
- Check the electricity supply and connections DIY safe
Ensure the boiler is properly plugged in or that its fused spur switch is turned on. A loose plug connection can occasionally cause control board errors. Do not open the boiler casing or interfere with any internal wiring.
- Call a Gas Safe registered engineer to diagnose and repair Gas Safe engineer
If the fault code returns after one or two resets, or if none of the above checks resolve the issue, a Gas Safe registered engineer must be called. They will test the fan output, inspect the air pressure switch with appropriate instruments, check the flue system internally, assess the ignition electrodes and ionisation sensor, and test gas pressure at the boiler. Any replacement of the fan, APS, gas valve, PCB, or burner components must be carried out by a registered professional.
Parts you may need
- Flue fan / combustion fan assembly · from £260
- Air pressure switch (APS) · from £55
- Ignition electrode · from £30
- Ionisation / flame sensing electrode · from £28
- Gas valve · from £150
- PCB (printed circuit board) · from £220
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£380, depending on the underlying cause.
Frequently asked questions
My Biasi boiler shows E24 — which meaning applies to my model?
The easiest way to tell is to check your boiler's model name, which is usually printed on a label inside the front panel or in the manual. If you have a Rinnova, the E24 code specifically relates to a flue or ventilation fault. If you have an older model such as a Riva, Riva Plus, Garda, or 24S, E24 points to a burner ignition failure. Both faults share some common causes — such as a faulty fan — so a Gas Safe engineer's diagnostic approach will cover both possibilities regardless.
Can I fix Biasi E24 myself, or do I always need an engineer?
There are a handful of checks you can safely carry out yourself: resetting the boiler (once or twice only), inspecting the external flue terminal for obvious blockages like leaves or a bird's nest, confirming your gas supply is on, and checking the boiler's plug or fused spur. Beyond these steps, the fault requires internal investigation — testing the fan, air pressure switch, ignition components, or gas valve — all of which must be done by a Gas Safe registered engineer. Attempting internal gas boiler repairs yourself is both illegal and potentially life-threatening.
How much does it typically cost to fix a Biasi E24 fault?
Most people with this fault pay somewhere between £120 and £380 once labour and parts are included. A straightforward fix such as cleaning ignition components or replacing an air pressure switch tends to sit at the lower end of that range. Replacing the fan usually brings the cost towards the upper end. In rare cases where the PCB needs replacing the bill can climb to £400–£500 or more, and on older Biasi boilers it is worth getting a new boiler quote alongside any repair quote above roughly £500, as replacement may be more economical in the long run.
Why does my Biasi keep coming back with E24 after I reset it?
A single reset clearing the fault temporarily usually means the fault condition is intermittent — perhaps a fan that is starting to fail, a partially blocked flue, or a gas supply that dips occasionally. If the code returns reliably within a short period of each reset, the underlying component has most likely failed and needs replacing. Repeated resets without diagnosis are not a solution and can mask a worsening fault; arrange for a Gas Safe engineer to investigate before the boiler fails completely, especially heading into colder weather.