Baxi E86 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E86 fault code mean?
The E86 code appears on Baxi boilers when one internal component has lost the ability to communicate with another — essentially, part of the boiler's electronics has stopped 'talking' to the rest of the system. Baxi uses a family of closely related codes (E83, E84, E85, E86, and E87) to flag these internal communication breakdowns; E86 is one specific variant within that group. When this handshake between components fails, the boiler locks out as a safety precaution rather than continuing to operate in an unknown state. The fault is almost always electrical in nature — a wiring problem, a loose connector, or a failing PCB — and it requires investigation inside the boiler casing to resolve fully.
General guidance only — not a substitute for professional advice. 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
- Loose or damaged wiring harness Common
Inside a boiler there is a network of wiring connecting sensors, the PCB, the gas valve, and other components. Vibration over time, or work carried out during a previous service, can cause connector plugs to work loose or wires to chafe and break. When a connection becomes intermittent or is lost entirely, the PCB registers a communication failure and triggers E86.
- Faulty or ageing PCB Common
The PCB acts as the brain of the boiler, co-ordinating signals between every component. As a boiler ages — typically beyond eight to ten years — the board's capacitors and solder joints can degrade, causing it to misread or lose signals from other parts of the system. This is one of the more expensive root causes to fix but is frequently behind persistent E86 lockouts on older Baxi units.
- Disconnected or failed internal component Sometimes
If a device such as a sensor, modulating valve actuator, or display board has been accidentally unplugged — or has failed and stopped responding — the PCB will detect the absence of expected communication and display E86. Reconnecting the device or replacing the faulty unit often clears the code.
- Component wear due to boiler age Sometimes
On boilers that are more than ten years old, general wear across multiple electronic components can cause marginal communication issues that show up as E86 without a single obvious culprit. In these cases an engineer may find several contributing factors rather than one clear-cut failure.
How to fix it
- Reset the boiler once DIY safe
Press and hold the reset button on your Baxi boiler for a few seconds until the boiler attempts to restart. A single reset is worth trying — occasionally a transient voltage spike or brief power interruption can trigger E86 without an underlying hardware fault. If the code clears and the boiler runs normally, monitor it over the next day or two. If E86 returns straight away or comes back repeatedly, do not keep resetting; move on to the next step and arrange professional diagnosis.
- Check that your gas supply is on DIY safe
Confirm that the gas isolation valve on the supply pipe to the boiler is fully open (handle parallel to the pipe) and that other gas appliances in your home, such as a hob or gas fire, are working normally. If there is no gas supply, contact your gas supplier rather than an engineer. This step rarely explains E86 but takes seconds to rule out.
- Visually inspect accessible wiring — do not touch internal components DIY safe
With the boiler switched off at the mains, you can look through the boiler casing (if the front panel is already open) for any obviously disconnected or burnt-smelling cables at the very front of the unit. Do not remove panels, reach inside, or disturb any wiring yourself. This is purely a visual check to give useful information to the engineer you call.
- Call a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
Because E86 points to an internal electrical communication failure, the investigation and repair must be carried out by a Gas Safe registered engineer. They will open the boiler, check the wiring harness for continuity, test the PCB for correct operation, and identify whether a component has failed. Depending on what they find, the repair may involve re-securing connectors, replacing damaged wiring, repairing or replacing the PCB, or swapping out a failed component. Always ask for a written quote before authorising expensive parts such as a PCB replacement.
Parts you may need
- Baxi PCB (main control board) · from £280
- Wiring harness · from £75
- Electrical connector/plug repair kit · from £20
- Sensor (NTC thermistor) · 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 £120–£400, depending on the underlying cause.
Frequently asked questions
Is E86 the same as E83, E84, E85, and E87 on a Baxi boiler?
They are closely related. Baxi uses all five codes — E83 through E87 — to flag internal communication failures between different pairs of components. The specific number can point an engineer towards which communication link has broken down, but the diagnostic process and likely causes are broadly the same for all five codes. If you see any of these on your display, the advice on this page applies.
Can I fix Baxi E86 myself?
Only a boiler reset is safe to attempt yourself. Everything else — checking wiring, testing the PCB, replacing components — must be done by a Gas Safe registered engineer. Working inside a boiler involves live electrical connections in a gas environment, and incorrect repairs can create a dangerous situation as well as invalidating your boiler warranty.
How much does it cost to fix Baxi E86 in the UK?
Most people pay between £120 and £400 depending on what the engineer finds. A straightforward wiring reconnection or minor repair typically costs £120–£200 including labour. If the PCB needs replacing, the total bill (part plus fitting) is usually £400–£650. PCB replacement is at the higher end and worth weighing against the age of the boiler — on a unit over ten years old, a full boiler replacement may offer better long-term value than a costly PCB repair.
Why does my Baxi boiler keep showing E86 after I reset it?
A fault that clears briefly on reset but returns quickly almost always indicates a genuine hardware problem — most likely a deteriorating PCB, a loose wiring connection that re-opens when the boiler heats up, or a component that has partially failed. Repeated resetting will not fix the underlying issue and may mask a worsening fault. Arrange a Gas Safe engineer visit so the root cause can be properly diagnosed and repaired.