Biasi ER10 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi ER10 fault code mean?
The ER10 code means your Biasi boiler has locked itself out after the flue temperature sensor — known as the flue NTC probe — detected a potentially unsafe condition. Either the flue gas temperature has climbed beyond acceptable limits, or the sensor itself has developed a fault and is sending incorrect readings to the control board. Either way, the boiler shuts down as a precaution to protect you and your home. You will need to identify whether the root cause is a genuine flue or ventilation issue, or a failing probe, before the boiler will run reliably again.
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 flue outlet Common
The most frequent trigger for ER10. If the flue terminal on the outside wall is partially or fully blocked — by a bird nest, accumulated debris, leaves, or even a cobweb across a small terminal — exhaust gases cannot escape freely. This causes flue temperatures to rise sharply and trips the safety lockout. Check the exterior terminal is clear and unobstructed.
- Faulty flue NTC temperature probe Common
The flue NTC probe works by changing its electrical resistance in proportion to temperature. Over time the probe can drift out of specification or fail outright, sending false or erratic signals to the PCB. Real-world cases show boilers locking out after just a few minutes of running, where the probe's resistance readings are only marginally outside the manufacturer's tolerance at room temperature — enough to confuse the control board into triggering a lockout.
- Exhaust gas recirculation due to incorrect flue installation Sometimes
If the flue terminal is positioned incorrectly — too close to a corner, a wall return, or another opening — combustion gases can be drawn back into the boiler's air intake. This raises measured flue temperatures and can cause repeated ER10 lockouts. This is a less common cause but is worth raising with an engineer if the fault reappears after a probe replacement.
- Wiring fault or loose connection at the probe Sometimes
Corroded terminals, a chafed cable, or a connector that has worked loose between the NTC probe and the PCB can cause resistance readings to spike or drop unexpectedly, mimicking a genuine over-temperature event. An engineer will inspect the wiring harness and connector block as part of any probe diagnosis.
How to fix it
- Visually inspect the flue terminal from outside DIY safe
Go outside and look at where the boiler's flue exits the building — usually a white or grey plastic terminal on an external wall. Check for obvious blockages such as bird nests, leaves, or debris. Do not attempt to access the flue internally or dismantle any pipework. If you spot a blockage at the terminal that you can safely clear from ground level without tools, do so.
- Check the boiler's gas supply is on DIY safe
Make sure the gas isolation valve on the pipe supplying the boiler is in the open position (handle in line with the pipe). Check that other gas appliances in your home — such as your hob — are working normally, which confirms gas is reaching the property.
- Reset the boiler — once or twice only DIY safe
Locate the reset button on the boiler's front panel (on most Biasi models this is clearly labelled). Press and hold it for roughly five to ten seconds until the display changes or the boiler attempts to restart. Allow up to ten minutes for the ignition sequence to complete. If the ER10 code returns, reset one more time. Do not reset more than two or three times in total — repeatedly forcing a lockout boiler to restart without fixing the underlying fault is unsafe.
- If the fault persists, stop resetting and call a Gas Safe registered engineer Gas Safe engineer
A returning ER10 after resetting points strongly to either a failing flue NTC probe or a flue installation problem — neither of which is safe or appropriate for a homeowner to investigate further. A Gas Safe engineer will use a multimeter to test the probe's resistance across a range of temperatures and compare the readings against Biasi's specifications. If the probe is out of tolerance, they will replace it with the correct genuine Biasi part (BI1782103 or BI1536104 depending on your model). They will also inspect the wiring, connectors, and flue routing for any secondary issues.
Parts you may need
- Biasi flue NTC temperature probe (BI1782103) · from £44
- Biasi flue NTC temperature probe (BI1536104) · from £30
- Flue probe wiring harness / connector · from £18
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–£220, depending on the underlying cause.
Frequently asked questions
Can I fix a Biasi ER10 fault myself?
The only steps a homeowner should take are checking the exterior flue terminal for obvious blockages, confirming the gas supply is on, and resetting the boiler once or twice. Any further diagnosis — testing the NTC probe with a multimeter, checking wiring, or inspecting the flue internally — must be carried out by a Gas Safe registered engineer. Interfering with sensors, wiring, or flue components without the correct qualifications is unsafe and may invalidate your boiler warranty.
How much does it cost to fix a Biasi ER10 fault?
For most households the repair involves replacing the flue NTC temperature probe, and total costs including engineer call-out, diagnosis, the part, and labour typically fall between £120 and £220. The probe itself costs roughly £25–£45 depending on the model variant. If the fault turns out to be a wiring issue the cost may be at the lower end; if the PCB has been damaged by a prolonged sensor fault the bill could be higher — worth discussing with your engineer before authorising work.
Why does my Biasi boiler keep showing ER10 even after I reset it?
A recurring ER10 after resetting almost always means the underlying cause has not been resolved. The two most likely culprits are a flue NTC probe that has drifted out of specification — sometimes by only a small margin — and a partially blocked or incorrectly positioned flue terminal. Repeated resets without fixing the root cause will not clear the fault and could place unnecessary strain on the boiler. Book a Gas Safe engineer to carry out a proper diagnosis.
Is my Biasi boiler still under warranty?
Biasi boilers typically carry a manufacturer's warranty of five to seven years depending on the model and when it was registered. If your boiler is within the warranty period, contact Biasi directly before arranging an independent repair, as warranty work must be carried out through approved channels to remain valid. Keep your installation paperwork and any previous service records to hand when you call.