Biasi E06 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E06 fault code mean?
The E06 (sometimes displayed as ER 06) fault code on Biasi boilers indicates that the central heating flow temperature sensor — known as the NTC (Negative Temperature Coefficient) probe — has either failed or is sending readings the boiler's control board considers implausible. This sensor monitors the temperature of water leaving the heat exchanger on its way to your radiators. When it stops working correctly, the boiler can no longer regulate heating safely, so it shuts down and locks out. You will need to reset the boiler to clear the lockout, but unless the underlying problem is resolved the fault will almost certainly return shortly afterwards. A Gas Safe registered engineer is required to diagnose and repair this fault properly.
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 NTC flow temperature probe Common
The probe itself has developed an internal fault — either an open circuit, a short circuit, or drift in its resistance characteristics — meaning it feeds the PCB inaccurate temperature data. This is the single most common root cause of E06 and is confirmed by testing the probe's resistance with a multimeter against the manufacturer's expected values.
- Loose or corroded wiring connections Common
The wiring loom between the NTC probe and the PCB can develop loose plug connections, broken wires, or corrosion at the terminals, particularly in older boilers or those in damp locations. This can mimic a probe failure without the probe itself being damaged, and is often the cheapest fix if caught early.
- Circulation pump issues Sometimes
If the pump is seized, air-locked, or running below the required flow rate, the water temperature at the flow sensor can spike or behave erratically. The PCB interprets this as a sensor anomaly and locks out. Pump problems are relatively common in boilers that have not been serviced regularly.
- Airlocks or heating sludge in the system Sometimes
Blockages caused by magnetite sludge, limescale, or trapped air restrict water flow through the heat exchanger. This can cause localised overheating near the flow sensor, producing readings that fall outside the expected range and triggering E06. Systems without a magnetic filter are particularly vulnerable.
- Faulty PCB Rare
Although less common, the printed circuit board itself can misinterpret signals from a perfectly healthy probe — especially if the board has suffered water ingress or component degradation. PCB failure is typically only confirmed after the probe and wiring have been ruled out.
How to fix it
- Attempt a boiler reset DIY safe
Locate the reset button on your Biasi boiler — usually a flame symbol or a dedicated button on the front panel — and hold it for around three seconds. If the boiler fires up and runs normally, monitor it over the next hour. If E06 returns quickly, the underlying fault has not been resolved and you should not keep resetting it repeatedly. Limit yourself to two or three attempts before calling an engineer.
- Check that your gas supply is working DIY safe
Make sure other gas appliances in the property (hob, gas fire) are working normally. If there is no gas supply, contact your gas supplier rather than an engineer. This is a basic sanity check — E06 is not a gas-supply fault, but it is worth eliminating before booking a call-out.
- Check system pressure DIY safe
Look at the pressure gauge on the boiler — it should read between 1.0 and 1.5 bar when the system is cold. If it is below 0.8 bar, top it up using the filling loop until it reaches around 1.2 bar, then attempt a reset. Low pressure alone will not cause E06, but it can accompany circulation problems that do.
- Inspect and test the NTC flow probe — Gas Safe engineer Gas Safe engineer
An engineer will disconnect the probe and measure its electrical resistance with a multimeter, comparing the reading against the resistance-temperature curve specified for that probe type. A reading that is open circuit, short circuit, or significantly out of range confirms the probe needs replacing. Biasi replacement probes are generally inexpensive and straightforward to fit.
- Check the probe wiring and connector plugs — Gas Safe engineer Gas Safe engineer
Even if the probe tests within range, the engineer will inspect the full wiring run for chafed insulation, broken conductors, and corrosion at the plug terminals. A contact cleaner or replacement connector can resolve the fault without needing to replace the probe itself.
- Inspect and bleed the circulation pump — Gas Safe engineer Gas Safe engineer
The engineer will check that the pump is spinning freely, bleed it via its bleed screw to release any trapped air, and verify it is delivering adequate flow. If the pump is seized or electrically faulty it will need to be replaced. Resolving a pump airlock can clear E06 if erratic flow was causing anomalous sensor readings.
- Consider a power flush if sludge is suspected — Gas Safe engineer Gas Safe engineer
If the system has a history of sludge problems, discoloured water from radiator bleed points, or cold spots on radiators, the engineer may recommend a power flush using specialist heating chemicals to clear debris from the circuit. Fitting a magnetic system filter afterwards helps prevent recurrence.
- Test or replace the PCB — Gas Safe engineer Gas Safe engineer
If the probe, wiring, and pump all test satisfactorily, the PCB is the likely culprit. The engineer will carry out board-level checks and, if a fault is confirmed, replace the PCB. This is the most expensive outcome for E06 and is typically only reached after all other components have been eliminated.
- Contact a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the boiler continues to display E06 after the basic homeowner checks above, book a Gas Safe registered engineer to carry out a full diagnosis. You can verify an engineer's registration at gassaferegister.co.uk. If your Biasi boiler is still within its warranty period (typically five to seven years depending on model), contact Biasi directly — a covered repair may be available at no cost.
Parts you may need
- Biasi NTC flow temperature probe · from £25
- Probe wiring harness / connector · from £20
- Circulation pump (Biasi compatible) · from £85
- Magnetic system filter (e.g. Adey MagnaClean) · from £75
- PCB (Biasi model-specific) · 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 £140–£350, depending on the underlying cause.
Frequently asked questions
Can I fix the Biasi E06 fault myself?
Not safely. The E06 code points to a problem with an internal temperature sensor or related components, all of which require a Gas Safe registered engineer to test and replace legally and safely. The only things a homeowner should do are: attempt a reset (up to two or three times), check the gas supply is on, and verify the system pressure is within the normal 1.0–1.5 bar range. If those checks do not resolve it, call an engineer.
How much does it cost to fix Biasi E06 in the UK?
The most common repair — replacing the NTC flow probe and checking the wiring — typically costs between £140 and £250 all in, including labour. If the problem turns out to be a seized pump, expect to pay roughly £200–£350 for a pump replacement. A power flush, if the system is heavily sludged, adds £300–£600 depending on system size. PCB replacement is the most expensive outcome and can reach £400–£500 or more for some Biasi models; because it is relatively rare for E06, we have not included it in the headline repair range, but it is worth being aware of if the engineer rules out simpler causes.
Why does my Biasi boiler keep showing E06 after a reset?
Resetting the boiler clears the lockout but does not repair the underlying fault. If E06 returns within minutes or hours of a reset, the NTC probe is almost certainly either faulty or receiving a bad signal due to a wiring issue or circulation problem. Repeated resets will not make the situation better and may mask a deteriorating component. You should limit resets to two or three attempts and then arrange for a Gas Safe engineer to investigate.
Is E06 the same as ER 06 on a Biasi boiler?
Yes — Biasi displays the same fault in slightly different formats depending on the model. Some boilers show 'E06' while others show 'ER 06' or 'ER06'. All three refer to the same NTC heating flow probe fault and are resolved in the same way. If you are unsure which model you have, check the data plate on the inside of the boiler casing or refer to your installation documentation.