Potterton E86 Fault Code: Causes, Fixes & Repair Costs
What does the Potterton E86 fault code mean?
The E86 code on a Potterton boiler signals a communication fault — meaning one or more components inside the boiler have lost the ability to exchange data correctly via the PCB (Printed Circuit Board). Potterton groups several related codes together in this area: E83, E84, E85, E86, and E87 all sit within the same communication-error family. Depending on your specific model, E86 (and its neighbours) can point to a breakdown in signalling from an NTC temperature sensor, a wiring connection failure, or a loss of communication with a connected room controller or wireless thermostat. Because the PCB acts as the central hub through which every component talks to the rest of the boiler, any broken link in that chain — whether it's a sensor, a wire, or the board itself — can trigger this code. Potterton's Promax, Assure, and Gold/Titanium ranges may interpret these codes slightly differently, so always cross-reference with your model's documentation if you are unsure.
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 disconnected NTC temperature sensor Common
NTC thermistors measure water temperature in the flow and return pipework and relay that data to the PCB. If an NTC sensor develops a fault, loses its connector, or drifts out of its acceptable resistance range, the PCB can no longer trust the temperature readings and raises a communication error. This is the most frequent root cause of E86 on Potterton boilers.
- Loose or damaged internal wiring Common
There are numerous low-voltage wiring looms inside a Potterton boiler routing signals between sensors, the fan, valves, and the PCB. A connector that has worked loose over time, a wire that has been chafed by a vibrating component, or a corroded terminal can all sever the communication path and trigger E86 without any component being genuinely broken.
- Room controller or wireless thermostat disconnection Sometimes
The E83–E87 code group on several Potterton models specifically covers the boiler losing contact with its room controller. Flat batteries in a wireless thermostat, a loss of RF pairing, or a broken cable on a wired controller can all cause this. The boiler interprets the missing signal as a communication fault and locks out.
- Failing or damaged PCB Sometimes
The PCB coordinates every signal in the boiler, so any degradation of the board itself — through component ageing, heat stress, or moisture ingress from a nearby leak — can cause apparently random communication errors including E86. A PCB fault is more expensive to resolve and is usually only confirmed after an engineer has ruled out sensors and wiring.
- Water ingress or internal leak near electronics Rare
A slow drip from a heat exchanger joint, a pump seal, or a pressure relief valve discharge can allow moisture to reach the PCB or wiring connectors. Even a small amount of condensation in the wrong place can cause intermittent short circuits that present as communication faults.
How to fix it
- Reset the boiler DIY safe
Press and hold the reset button on the boiler's control panel for 3–5 seconds (the exact location varies by model — check your user guide). A single reset clears many transient sensor errors. If the E86 returns within a short time, do not keep resetting repeatedly — more than two or three attempts is unlikely to help and may mask a developing fault.
- Check your room controller or wireless thermostat DIY safe
If you use a wireless thermostat or a smart room controller, replace the batteries and check that the device is within range of the boiler receiver. For a wired controller, visually inspect the cable where it enters both the thermostat and the boiler for obvious damage or loose connections. Re-pair the device if your controller supports that option. This is a quick, free check worth doing before calling an engineer.
- Verify the boiler's system pressure DIY safe
While not a direct cause of E86, low system pressure (below around 1 bar on the pressure gauge) can cause the boiler to behave erratically. If the gauge reads below 1 bar, top up via the filling loop until the needle sits between 1 and 1.5 bar. If pressure is already normal, skip this step.
- Call a Gas Safe registered engineer to diagnose internal components Gas Safe engineer
If the fault persists after the checks above, the cause lies inside the boiler — the NTC sensor resistance, PCB integrity, and internal wiring all need to be tested with specialist diagnostic equipment. Only a Gas Safe registered engineer should open the boiler casing and carry out these tests. The engineer will identify whether the fix is a straightforward sensor swap, a wiring repair, or a PCB replacement, and advise you on cost versus the age of the appliance before proceeding.
Parts you may need
- NTC thermistor (flow or return sensor) · from £25
- Wiring loom / sensor harness · from £45
- PCB (Printed Circuit Board) · from £180
- Wireless receiver / room controller kit · from £90
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 £100–£350, depending on the underlying cause.
Frequently asked questions
Can I fix the Potterton E86 fault myself?
The safe DIY steps are limited to resetting the boiler, checking your room thermostat batteries and pairing, and confirming system pressure is correct. Beyond that, diagnosing and replacing NTC sensors, repairing wiring, or changing the PCB all require working inside the boiler casing — this must be carried out by a Gas Safe registered engineer. Attempting internal repairs yourself is unsafe and could void any remaining warranty or insurance cover.
How much does it cost to fix a Potterton E86 fault in the UK?
Most people pay between £100 and £350. A straightforward NTC sensor replacement or wiring repair typically falls in the £100–£200 range including labour, while a new room controller or thermostat kit sits around £120–£300 fitted. If the PCB is at fault, expect to pay considerably more — PCB replacement on Potterton boilers commonly runs to £350–£650 depending on parts availability and your location, with engineers in London and the South East tending toward the upper end. Always ask for a written quote before authorising any work.
What is the difference between Potterton fault codes E83, E84, E85, E86, and E87?
These five codes all belong to the same communication-error family on Potterton boilers. In practice they point to closely related issues: faults with NTC temperature sensors, internal wiring failures, or a loss of contact with the room controller. The specific code displayed can help an engineer narrow down which sensor or circuit is affected, but the diagnostic and repair process is broadly the same across the group. If your boiler is showing any of these codes and a reset does not clear it, the advice is identical — contact a Gas Safe registered engineer.
Is it worth repairing a Potterton boiler with an E86 fault, or should I replace it?
For a relatively young boiler (under ten years old), repairing a sensor or wiring fault at £100–£200 is almost always worthwhile. If the diagnosis points to a PCB replacement costing £400 or more, it is sensible to weigh that against the age and overall condition of the boiler. A boiler over 12–15 years old with a major component failure may be approaching the end of its economically viable life, and a new boiler with a manufacturer's warranty could work out better value in the long run. Ask your engineer for an honest appraisal before committing to an expensive repair.