Biasi E23 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E23 fault code mean?
The E23 code on a Biasi boiler indicates that the PCB (printed circuit board) is attempting to communicate with the gas valve modulator coil — the component responsible for controlling the rate of gas flow and therefore the flame size — but is receiving no response. In Biasi's own service documentation this is logged as 'E23: gas valve modulator disconnected'. The boiler will typically lock out as a safety precaution. Because this fault sits within the E20–E23 group (covering defective electromagnetic solenoid conditions), the underlying issue could be a disconnected wiring plug, a failed modulator coil, a faulty gas valve assembly, or in some cases a PCB that is no longer driving the modulator correctly. A Gas Safe registered engineer is needed to pinpoint which component is at fault.
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
- Disconnected or corroded wiring connector Common
The most frequent cause. The electrical connector linking the wiring loom to the gas valve modulator coil can work loose over time — particularly as the boiler heats and cools through thousands of cycles — or the terminals may have corroded, breaking the circuit and triggering the fault.
- Failed gas valve modulator coil Common
The modulator coil itself may have burned out or developed an open circuit internally. An engineer can confirm this quickly by measuring the coil's resistance with a multimeter; a reading outside the manufacturer's specified range confirms coil failure.
- Defective gas valve assembly Sometimes
If the modulator coil is part of an integrated valve body, or if the valve has suffered internal damage, the entire gas valve assembly may need replacing. The valve body and modulator are often supplied as one unit for Biasi models.
- PCB no longer driving the modulator Rare
If the wiring and the valve itself both check out correctly, the fault may originate in the PCB, which is responsible for sending the drive signal to the modulator. A failing output circuit on the board can mimic a disconnection fault.
How to fix it
- Note the exact fault code and attempt a single reset DIY safe
Press and hold the boiler's reset button for 3–5 seconds as described in your user manual. If the boiler fires up normally and the code does not return within a day or two, monitor it closely. Do not reset more than two or three times in total — if the code keeps returning, further resets will not resolve the underlying fault and a Gas Safe engineer should be called without delay.
- Check your gas supply is on DIY safe
Confirm that other gas appliances in the property (such as a gas hob) are working normally. If they are not, contact your gas supplier rather than an engineer, as the issue may be with the supply rather than the boiler.
- Call a Gas Safe registered engineer to inspect the wiring loom and connectors Gas Safe engineer
An engineer will trace the wiring from the PCB to the gas valve modulator and check every connector for looseness, corrosion, or damage. This is not a job for a homeowner — even if a plug appears accessible, working near a gas valve and live boiler wiring carries serious safety risks.
- Engineer to test the modulator coil resistance Gas Safe engineer
Using a multimeter, the engineer measures the resistance of the modulator coil. A reading outside the acceptable range confirms the coil has failed and needs replacement, usually as part of the full gas valve assembly.
- Engineer to verify gas valve operation and inlet pressure Gas Safe engineer
The engineer will also confirm that the gas valve is mechanically sound and that the gas inlet pressure at the boiler meets Biasi's specification. An incorrect supply pressure can contribute to valve-related faults.
- Engineer to test or replace the PCB if wiring and valve are confirmed good Gas Safe engineer
Where the wiring loom and gas valve both pass inspection, the PCB's modulator-drive circuit is suspect. The engineer may be able to test the output signal directly; if the board is at fault it will need replacing. Note that PCBs are among the more expensive boiler components, so weigh the repair cost against the boiler's age and overall condition.
- Replace the gas valve assembly if the modulator coil or valve body is faulty Gas Safe engineer
Biasi gas valves are typically replaced as a complete unit. Parts are widely available from UK suppliers such as Parts Center and HRPC, often on next-day delivery. Only a Gas Safe registered engineer may legally carry out this work.
Parts you may need
- Biasi gas valve assembly (including modulator coil) · from £110
- Biasi PCB (model-specific) · from £145
- Wiring loom / harness · from £35
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 E23 code dangerous?
The boiler locks itself out when E23 appears, which means it stops burning gas — so there is no immediate danger from the fault itself. However, you should not attempt to bypass or repeatedly reset the lockout, and the fault must be properly diagnosed and repaired by a Gas Safe registered engineer before the boiler is returned to normal use.
Can I fix the E23 fault myself?
No. A single reset is the only action a homeowner should take. The fault points directly to the gas valve modulator or its wiring — both of which are within the gas-carrying parts of the boiler. Only a Gas Safe registered engineer is legally permitted to work on these components, and attempting DIY repairs could be unsafe and would invalidate your warranty.
How much does it cost to fix a Biasi E23 fault?
For most people the repair falls between £150 and £380 depending on what the engineer finds. A wiring connector issue or coil replacement at the cheaper end, a full gas valve assembly in the middle, and a PCB replacement at the upper end. If both the gas valve and PCB need replacing on an older boiler, costs could push higher — in that situation it is worth getting a new boiler quote for comparison, as a rule of thumb suggests replacing rather than repairing when a single repair quote exceeds around £500.
Is my Biasi boiler still under warranty?
Biasi offers a 5–7 year warranty depending on the model. If your boiler is within this period, contact Biasi directly before paying for an independent repair — a warranty claim could cover the cost of parts and labour entirely. You will typically need proof of annual servicing to keep a warranty valid, so have your service records to hand when you call.