Biasi E25 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E25 fault code mean?
The E25 code appears on Biasi boilers — including the Binova and Rinnova ranges — when the boiler detects an insufficient or inconsistent gas supply during normal operation. The boiler locks itself out as a safety precaution. Biasi's own guidance points to three areas to verify: that the gas connection is correct, that the flue outlet is clear and open, and that the gas pressure gauge (manometer) is functioning properly. Until the underlying cause is identified and resolved, the boiler will refuse to fire.
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
- Low or interrupted mains gas supply Common
If the gas pressure arriving at the boiler is too low or cuts out momentarily, the boiler will trigger E25. Check whether other gas appliances in the home — such as a hob or gas fire — are also failing to work. If they are, the issue may lie with your gas supplier or meter rather than the boiler itself.
- Faulty or stuck gas valve Common
The gas valve controls the flow of gas into the burner. Over time it can stick, wear out, or become partially blocked, preventing the boiler from receiving a steady supply during operation. An intermittent or incorrectly adjusted valve is a frequent cause of mid-operation lockouts showing E25.
- Blocked or obstructed flue Sometimes
Biasi specifically includes flue checks in the E25 diagnostic guidance. A blocked flue outlet — caused by bird nests, debris, or frost — can trigger safety sensors and cause the boiler to shut down. Inspect the external flue terminal for obvious blockages, but leave any internal flue work to an engineer.
- Faulty manometer (gas pressure gauge) Sometimes
The manometer monitors gas pressure and feeds information to the boiler's control system. If the gauge itself is defective, it can report false pressure readings that cause the boiler to lock out even when the actual gas supply is adequate.
- PCB or internal wiring fault Rare
Wiring faults or a failing printed circuit board can disrupt the signals between the gas valve and the boiler's control system, producing a gas supply fault code when the physical gas supply is actually fine. This is a diagnosis-by-elimination finding that requires a Gas Safe engineer to assess safely.
How to fix it
- Check other gas appliances in the home DIY safe
Before doing anything to the boiler, try your gas hob or another gas appliance. If nothing gas-powered is working, the problem is almost certainly with your wider gas supply. Contact your gas supplier or call the National Gas Emergency line on 0800 111 999.
- Reset the boiler once or twice DIY safe
Turn the boiler off at the mains, wait at least 10 seconds, then switch it back on. Use the reset button as described in your model's manual. A single reset is worth attempting in case the lockout was caused by a one-off interruption. If E25 returns promptly after resetting, do not keep repeating it — the underlying fault needs proper diagnosis.
- Check the external flue terminal for obvious blockages DIY safe
Go outside and visually inspect the flue outlet on the exterior wall or roof. Look for bird nests, leaves, or debris blocking the terminal. Do not attempt to dismantle or modify the flue yourself — if you spot a blockage you cannot safely clear from the outside, report it to your engineer.
- Do not attempt to adjust or replace the gas valve Gas Safe engineer
The gas valve is a safety-critical component. Any adjustment, cleaning, or replacement must be carried out by a Gas Safe registered engineer. Working on gas components without registration is illegal and extremely dangerous.
- Do not attempt to inspect or replace the PCB or internal wiring Gas Safe engineer
Internal wiring and circuit board faults require specialist diagnostic equipment and carry a serious risk of electric shock or gas-related hazard. Leave all internal electrical work to a qualified professional.
- Call a Gas Safe registered engineer to diagnose and repair Gas Safe engineer
If the fault persists after one or two resets, book a Gas Safe registered engineer. They will measure incoming gas pressure with calibrated equipment, test the gas valve, inspect the flue internally, check the manometer, and assess the PCB and wiring. Always ask to see an engineer's Gas Safe ID card before allowing any work to begin.
Parts you may need
- Gas valve · from £95
- Manometer (gas pressure gauge) · from £35
- Flue terminal/outlet assembly · from £40
- PCB (printed circuit board) · from £180
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 £150–£320, depending on the underlying cause.
Frequently asked questions
Can I fix the Biasi E25 fault myself?
The only safe DIY steps are checking other gas appliances to rule out a wider supply issue, inspecting the external flue terminal for obvious debris, and resetting the boiler once or twice. Any work involving the gas valve, internal wiring, PCB, or gas pressure testing must be done by a Gas Safe registered engineer. Working on gas components without registration is illegal in the UK.
How much does it cost to fix a Biasi E25 fault?
Most people with this fault pay somewhere between £150 and £320 all-in, depending on what the engineer finds. A gas valve replacement with labour typically falls in the £150–£220 range. A flue inspection and clearance is usually £80–£150. If the fault turns out to be a failed PCB, parts alone can cost £150–£300 or more, pushing the total higher — in that scenario it is worth weighing up the repair cost against a replacement boiler, particularly if the unit is outside its warranty period.
Why does E25 keep coming back after I reset it?
A reset clears the lockout but does nothing to address the underlying cause. If E25 returns after each reset, something is genuinely wrong — most likely a gas valve that is beginning to fail, an intermittent gas pressure problem, or a sensor or PCB issue. Repeatedly resetting without repair can mask the problem and delay a fix. Book an engineer if the code reappears more than once.
Is my Biasi boiler still under warranty?
Biasi typically offers warranties of five to seven years depending on the model. If your boiler is still within this period, contact Biasi directly before paying for independent repairs — a warranty claim could cover parts and labour at no cost to you. Keep your installation paperwork and any service records to hand when you call.