Biasi E110 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E110 fault code mean?
The E110 code appears on Biasi boilers — including the Inovia and Advance Plus ranges — when the built-in safety thermostat detects that the boiler's internal temperature has climbed to an unsafe level and has shut the appliance down as a precaution. On older Biasi models such as the Riva Plus and Garda, this same condition may be shown as A02 rather than E110. In either case, the boiler will not restart until the root cause of the overheating is identified and resolved. You may notice a complete loss of heating and hot water, and in some cases banging or gurgling sounds that indicate poor water circulation within the system.
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 system pressure Common
When the boiler's system pressure drops below roughly 1.0 bar, there is insufficient water in the circuit to carry heat away from the heat exchanger efficiently. This causes localised temperatures to spike and the safety thermostat to trip. Pressure can fall due to a small leak, air escaping after bleeding radiators, or natural system losses over time.
- Faulty or seized circulation pump Common
The pump is responsible for keeping heated water moving around the system continuously. If it has seized — often due to prolonged inactivity in summer, internal sludge, or wear — water sits stationary in the heat exchanger and overheats rapidly. A partially working pump that runs too slowly can cause exactly the same problem.
- Blocked heat exchanger or system sludge Common
Black iron oxide sludge, limescale from hard water, or debris can restrict water flow through the heat exchanger. With less water able to pass through, heat builds up in one spot until the safety thermostat trips. Boilers that have not been serviced regularly or systems without a magnetic filter are most at risk.
- Trapped air creating an airlock Sometimes
Air pockets in the heating circuit can block the path of water just as effectively as a physical blockage, causing hot spots to develop. This often happens after the system has been drained or after radiators have been bled without the boiler being repressurised correctly afterwards.
- Faulty NTC temperature sensor Sometimes
The NTC thermistor continuously monitors water temperature and feeds that data to the PCB. If the sensor has drifted out of calibration or developed an intermittent fault, it may report a dangerously high temperature when the water is in fact fine, causing a spurious E110 lockout.
- Failed safety thermostat Rare
The safety thermostat itself can deteriorate over time and begin tripping at temperatures lower than its rated threshold. If an engineer has already confirmed that circulation and temperatures are normal but E110 keeps returning, a faulty stat is a strong suspect.
How to fix it
- Check the pressure gauge and top up if needed DIY safe
Look at the pressure gauge on the boiler's front panel. When the system is cold it should sit between 1.0 and 1.5 bar — ideally around 1.2 bar. If it reads below 1.0 bar, locate the filling loop (usually a braided flexible hose or a built-in key valve beneath the boiler) and slowly open it until the gauge reaches 1.2–1.5 bar, then close it firmly. If you are unsure where the filling loop is, consult your boiler's user guide.
- Bleed any radiators that feel cool at the top DIY safe
Cold patches at the top of one or more radiators suggest trapped air. Use a radiator bleed key to open the bleed valve — a quarter turn is enough — and hold a cloth beneath it. Once water starts to trickle out steadily instead of air hissing, close the valve. Check the boiler pressure again afterwards and top up if it has dropped.
- Reset the boiler — but only once or twice DIY safe
With the pressure restored, press and hold the reset button (refer to your model's user guide for its exact location) for around three seconds. Allow the boiler to run through its ignition sequence. If it lights and runs normally, monitor it over the next few hours. If E110 returns within a short time, do not keep resetting — this indicates an underlying fault that needs an engineer's diagnosis.
- Listen and observe while the boiler runs DIY safe
If the boiler restarts, listen for any unusual sounds: loud banging (kettling) points to limescale or sludge in the heat exchanger, while persistent gurgling suggests air still in the system. Note these observations and report them to the engineer, as they help with diagnosis.
- Call a Gas Safe registered engineer to investigate further Gas Safe engineer
If E110 returns after a reset, or if you cannot identify a simple pressure or air issue, a Gas Safe registered engineer must carry out the diagnosis. They will check pump operation and flow rate, inspect the heat exchanger for scale or sludge, test the NTC sensor and safety thermostat with appropriate instruments, and check for any leaks that may be causing repeat pressure loss. Do not attempt to open the boiler casing, touch the pump, or interfere with any internal components yourself.
Parts you may need
- Circulation pump · from £120
- NTC temperature sensor · from £25
- Safety thermostat (overheat stat) · from £20
- Magnetic system filter (e.g. Magnaclean) · from £65
- Filling loop assembly · from £15
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–£420, depending on the underlying cause.
Frequently asked questions
Can I just keep resetting my Biasi boiler to clear the E110 code?
Resetting once or twice is reasonable to see whether the fault clears — for example, after you have topped up the pressure. However, E110 is a safety lockout triggered by genuine overheating, so repeatedly resetting without fixing the underlying cause risks damaging the heat exchanger or other components. If the code returns after one or two resets, stop and call a Gas Safe registered engineer.
How much does it typically cost to fix a Biasi E110 fault in the UK?
For most households the repair falls in the range of £150–£420 depending on what the engineer finds. Replacing an NTC sensor or safety thermostat usually sits toward the lower end (around £150–£300 including labour), while fitting a new circulation pump tends to cost £280–£420. If the system is heavily sludged and requires a powerflush, expect to pay £350–£600 on top of any component costs — though a powerflush also benefits the whole system and can extend its life significantly.
Is the Biasi E110 the same fault as A02 on older models?
Yes, functionally they are the same condition — the safety thermostat has tripped due to overheating. Older Biasi boilers such as the Riva Plus and Garda used an ER/A-style code system, and A02 indicated the same overheat lockout that newer Inovia and Advance Plus models display as E110. The diagnostic and repair approach is identical regardless of which display format your boiler uses.
How can I prevent the E110 fault from coming back?
The most effective steps are: having the boiler serviced annually by a Gas Safe registered engineer; fitting a magnetic filter (such as a Magnaclean) to catch iron oxide sludge before it reaches the heat exchanger; considering a powerflush if the system has never had one; and — in hard-water areas — discussing scale inhibitor dosing or a water softener with your engineer. Keeping system pressure topped up and bleeding radiators when needed also reduces the risk of recurrence.