Biasi E10 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E10 fault code mean?
The E10 (also displayed as ER 10) fault code means your Biasi boiler has shut itself down — locked out — because the flue gas probe or thermal fuse has intervened. These components sit within the flue circuit and monitor flue gas temperatures during combustion. When either one detects conditions outside safe operating limits, the boiler cuts out immediately as a precaution. This is a safety lockout, not a nuisance trip, so the boiler will not restart on its own until the underlying cause is identified and resolved. A single reset may clear it temporarily, but if the code returns, there is a genuine fault that needs a Gas Safe registered engineer to investigate.
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
- Faulty or degraded flue gas NTC probe Common
The flue gas temperature sensor (NTC probe) is the primary component named in Biasi's own service documentation for this lockout. Over time the probe can drift out of calibration, develop a poor electrical connection, or fail outright, causing the boiler to lock out even when flue temperatures are actually within safe bounds. This is the most frequently replaced part when E10 appears.
- Tripped or failed thermal fuse Common
A thermal fuse sits in the flue circuit as a last-resort safety device. If it has blown — either because of a genuine overheat event or because it has reached the end of its service life — the boiler will lock out with E10. Biasi's service guidance recommends replacing the thermal fuse on a scheduled basis regardless of apparent condition, so an ageing fuse on an older boiler is a very plausible cause.
- Blocked or obstructed flue outlet Common
If the external flue terminal is partially or fully blocked — by a bird's nest, accumulated debris, ice in cold weather, or a nearby structure — combustion products cannot escape properly. This causes flue gas temperatures to rise rapidly, tripping the probe or thermal fuse. The flue terminal is the one homeowner-visible check worth making before calling an engineer.
- Overheating in the combustion or flue circuit Sometimes
A problem elsewhere in the boiler — such as a failing circulating pump, restricted water flow, or a partly blocked heat exchanger — can cause localised overheating that raises flue gas temperatures above the threshold the probe is set to detect. In this scenario E10 is a symptom of another underlying issue rather than a probe fault in itself.
- Faulty PCB or wiring fault Rare
If the signal wiring between the flue probe and the main PCB is damaged, corroded, or has a loose connection, the PCB may receive a false reading and trigger the E10 lockout. A full PCB failure can also produce this code. Both are less common than probe or fuse faults but should be checked if the probe and fuse test correctly.
How to fix it
- Check the external flue terminal for obstructions DIY safe
Go outside and locate the flue outlet — usually a white or grey plastic terminal on an external wall or through the roof. Look for bird nests, leaves, ice build-up, or anything else blocking the opening. If there is a visible obstruction you can safely remove without climbing or working at height, clear it. Do not attempt to access the flue internally or remove any boiler casing.
- Reset the boiler — once or twice only DIY safe
If the flue terminal looks clear, attempt a single reset using the reset button on the boiler's front panel. Hold it for the duration described in your boiler's user guide (typically 3–10 seconds) until the display changes. Allow the boiler a minute or two to complete its start-up sequence. If E10 clears and heating is restored, monitor the boiler closely. If the fault returns within a short period, do not keep resetting — a maximum of two or three resets is the safe limit, after which further cycling without repair serves no purpose.
- Check your boiler is still within its warranty period DIY safe
Biasi boilers typically carry a manufacturer warranty of five to seven years depending on the model and registration status. If your boiler is still within that window, contact Biasi directly before paying for a private repair — a warranty claim could cover parts and labour at no cost to you.
- Call a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
If the E10 code returns after resetting, or if you are unsure of the flue terminal condition, contact a Gas Safe registered engineer. They will inspect the flue circuit, test the NTC probe's resistance against Biasi's specification, check the continuity and condition of the thermal fuse, examine wiring connections to the PCB, and assess whether any overheating condition contributed to the lockout.
- Engineer to test and replace the flue gas NTC probe if faulty Gas Safe engineer
Using a multimeter, the engineer will check the probe's resistance at a known temperature and compare it against the manufacturer's data. An out-of-range reading confirms the probe has failed and needs replacing. This is an internal component replacement requiring the boiler casing to be opened — Gas Safe work only.
- Engineer to inspect and replace the thermal fuse Gas Safe engineer
The engineer will test the thermal fuse for continuity. A blown fuse will show as an open circuit and must be replaced. Even if the fuse tests as intact, if it is significantly aged the engineer may recommend proactive replacement in line with Biasi's servicing guidance. The root cause of any overheat event that tripped the fuse must also be established and corrected.
- Engineer to check the PCB and wiring harness if probe and fuse are both serviceable Gas Safe engineer
If the probe and thermal fuse both test correctly, the engineer will inspect the wiring loom for chafing, corrosion, or loose terminals, and assess the PCB for signs of damage. A faulty PCB will need replacement, which is one of the higher-cost outcomes for this fault code.
Parts you may need
- Biasi flue gas NTC temperature probe · from £45
- Thermal fuse (flue circuit) · from £20
- Flue gas probe wiring harness · from £35
- PCB (main control 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–£380, depending on the underlying cause.
Frequently asked questions
Is the Biasi E10 fault dangerous — can I keep using the boiler?
You should not attempt to keep the boiler running by repeatedly resetting it. The E10 lockout exists because a safety device in the flue circuit has detected a potentially dangerous condition — whether that is excessive flue gas temperature, a failed probe giving a false reading, or something else. Running the boiler without identifying the cause is not safe practice. One or two resets to see whether a transient fault clears is reasonable; beyond that, treat it as a fault requiring engineer attention and leave the boiler off until it has been inspected.
How much does it cost to fix a Biasi E10 error in the UK?
For the most common causes — flue NTC probe replacement or thermal fuse replacement — most homeowners pay somewhere between £150 and £380 including parts and labour. A straightforward probe swap at the lower end of that range is probably the most typical outcome. If the fault turns out to be a PCB failure, costs can rise to £300–£500 or more depending on the model and engineer's rates. As a rough rule of thumb, if a repair quote comes in at around £500 or above on an older boiler, it is worth getting a new boiler quote for comparison.
How often should the thermal fuse on a Biasi boiler be replaced?
Biasi's own service documentation recommends that the thermal fuse in the flue circuit is replaced on a scheduled basis — this is something your Gas Safe engineer should be aware of and ideally carry out during an annual service on an affected model. If your boiler has not been serviced regularly, the fuse may be well past the point at which proactive replacement would have been recommended, making it a likely candidate when E10 appears.
Why does my Biasi boiler show E10 in winter but seem fine in summer?
Cold weather can cause the external flue terminal to ice up, particularly on boilers where the flue exits through a wall in an exposed location. Ice — or even a thick frost — can partially restrict the flue outlet, causing combustion gases to back up and flue temperatures to spike, tripping the probe. If E10 appears consistently during cold snaps and clears after a reset once temperatures rise, a frozen or restricted flue terminal is worth investigating. Insulating an exposed condensate pipe is a separate but related cold-weather check worth making at the same time.