Overview
E83 / E84 / E85 / E86 / E87 on Potterton Assure combi or system boilers indicate a communication fault between the boiler and its room controller or external control unit. In plain terms the boiler is not receiving or cannot exchange the expected signal with the thermostat, programmer, wireless receiver or other control device. The codes are essentially variations of the same problem and point to an interruption in the control link rather than a gas, flame or primary hydraulic fault. This fault is usually caused by a broken or loose wire, poor connector, flat batteries in a wireless thermostat, a failed room controller or receiver, radio interference or an internal boiler communications module / PCB problem. Severity is moderate: the immediate risk to safety is low (this code does not itself indicate a gas leak or combustion fault) but it will commonly stop the boiler from responding to heating or hot water demands, leaving the property without heating or hot water until the link is restored. Basic checks and resets can be done by a competent homeowner, but any work that involves opening the boiler, testing live low-voltage connectors on the PCB or replacing internal modules should be carried out by a Gas Safe registered heating engineer.
Possible Cause: Communication error
Troubleshooting Steps
Safety precautions:
- Do not open the boiler casing or attempt internal repairs unless you are a qualified Gas Safe engineer. The boiler contains live electrical parts and gas components. Electrical isolation and gas work must be done by a professional.
- Before doing any external wiring checks, switch off the boiler at the isolator or mains and make sure you know how to safely isolate power. If you are unsure, do not proceed and call a professional.
Initial checks a homeowner can safely do:
1. Record the exact error code(s) and behaviour, and take a photo of the display. Note whether heating, hot water or both are affected.
2. Reset the boiler using the reset button or procedure in the user manual. Wait a few minutes to see if the code clears and whether the boiler responds to thermostat demand. A cleared code could indicate a transient fault.
3. Check the room thermostat or room controller:
- For battery-powered or wireless thermostats: check and replace batteries, confirm the thermostat display is active, and ensure it is set to call for heat (set temperature above room temp).
- For smart or app-controlled systems: check the hub or bridge is online, the app shows the thermostat as connected, and the schedule or hold mode is not preventing a call for heat.
4. If you have a wired thermostat and are comfortable doing basic checks externally: inspect visible thermostat wiring and the thermostat unit for loose terminals or damaged cable sleeving. Do not strip insulation, probe live terminals, or open the boiler.
5. Check other controls: timers, motorised valves or external switching devices that sit between the controller and boiler. Ensure they are powered and calling for heat when expected.
6. Check mains power to the boiler and any separate receiver boxes (if present). Ensure the receiver has power and any LED indicators show normal operation.
Diagnostic and possible fixes (homeowner-level and what to prepare for an engineer):
1. Wireless systems: try re-pairing the thermostat and receiver according to the thermostat manual. Replace batteries in the thermostat and any battery-backed receivers. Move the thermostat temporarily closer to the boiler or receiver to rule out range or interference issues.
2. Wired systems: if the thermostat wiring is accessible at a convenient junction box (not inside the boiler), visually inspect for loose or corroded connections and securely re-tighten terminal screws if you are confident doing so with the power isolated. If you are not certain, stop and call a professional.
3. Check for recent work or disturbances: water leaks, building works, or pest damage can affect cables and connectors; if found, inform the engineer.
4. If the error returns after reset and simple fixes, log whether it is intermittent or constant and any pattern (e.g., only after power cuts, only at night, only when the smart system updates). This helps diagnosis.
5. Provide the engineer with the thermostat model, any smart hub details, photos of wiring and the boiler display, and a record of the steps you have already tried.
When to call a professional and what they will do:
- Call a Gas Safe registered heating engineer if the code persists after basic checks, if you need the boiler casing opened, if PCB or receiver replacement is suspected, or if any work requires live voltage checks or gas isolation. The engineer will measure voltages, check continuity between the room controller and the boiler terminals, test the boiler communications board and receiver module, and replace faulty components such as the room thermostat, wireless receiver or the boiler PCB if required.
- Inform the engineer of the exact code, what controls you use (wired, wireless, smart), and the troubleshooting steps you have already completed.
Final notes:
- Avoid attempting internal boiler repairs yourself. Communication faults are often simple wiring or receiver issues but can also indicate PCB or module failure which requires specialist testing and safe replacement.
- A quick reset and checking thermostat batteries or app connectivity often fixes temporary communication errors, but persistent or recurring codes should be investigated by a Gas Safe engineer to restore reliable and safe operation.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Potterton Assure Combi and system.