Overview
E83 / E84 / E85 / E86 / E87 on Potterton Promax Ultra, Gold or Titanium boilers indicates a communication fault between the boiler and the room controller (thermostat). In plain terms the boiler is not receiving the temperature/control signals from the room thermostat or controller. This can be caused by a lost wireless link, flat batteries in the controller, damaged or loose wiring on a wired thermostat, a failed thermostat or RF receiver module, or an internal PCB issue within the boiler. Severity is generally moderate: it is not normally an immediate gas safety emergency, but it will often prevent normal heating or hot water control so the property can be left without heating or hot water. That can be serious in cold weather (risk of frozen pipes) or for vulnerable occupants. Many causes are basic and can be checked or fixed by a homeowner (batteries, controller settings, simple resets). Anything that requires opening the boiler, working on mains wiring, or investigating the boiler PCB or gas components should be left to a qualified engineer (Gas Safe registered in the UK).
Possible Cause: No communication between room controller and boiler
Troubleshooting Steps
Safety precautions:
1) Do not open the boiler casing, touch gas components, or attempt internal PCB repairs. Those tasks must be done by a Gas Safe qualified engineer. 2) Isolate electrical supply at the fused spur or consumer unit before working on thermostat wiring. 3) If you smell gas, evacuate the property and call the gas emergency number immediately.
Initial checks a homeowner can do:
1) Check the room controller/thermostat is powered and its display is normal. Replace the batteries with fresh ones even if the display seems OK. 2) Ensure the thermostat is calling for heat (set target temperature higher than room temperature or use the controller’s call-for-heat/manual boost). 3) Check the boiler display for the same E8x error and note any other messages or LEDs. 4) Check the controller location and distance: temporary interference or being too far from the boiler can disrupt a wireless signal. 5) Reboot the boiler: switch the boiler off at its fused spur or isolator, wait 30 seconds, then switch back on. Note whether the E8x code clears and whether the boiler responds to the thermostat again.
Specific diagnostic and fix steps (step-by-step):
1) If reset cleared the code but it returns, try replacing batteries in the room controller and test again. 2) If you have a wireless thermostat, check its pairing status in the thermostat manual. Attempt a re-pair following the manufacturer instructions: usually this means putting the thermostat into pairing mode and activating the boiler receiver pairing mode (consult both manuals). 3) For wired thermostats, switch off mains to the boiler, remove the thermostat wiring cover and check the low-voltage control wires are tight on the correct terminal block (consult the boiler manual for the correct terminals). Look for loose, corroded or broken wires. If you find damaged wiring, call a qualified electrician or heating engineer to replace or reterminate the cable. 4) If the boiler has a separate RF receiver module (some models do), try to determine if the receiver shows any LED status indicators; a receiver fault or unplugged connector can cause the E8x family of errors. Do not open the boiler to inspect the receiver — instead, record the symptoms and call an engineer. 5) If re-pairing or wiring checks do not restore communication, note whether other controls (programmer, hot water demand) are working. Take photos of the boiler display and the thermostat display and make a note of when the fault started, and any changes made.
When to call a professional:
1) Call a Gas Safe registered heating engineer if the error persists after simple home checks (battery replacement, reset, re-pairing, wiring inspection). 2) Call a qualified engineer or electrician if any mains wiring, internal boiler wiring, PCB or RF receiver connections require inspection or replacement. 3) Call immediately if you smell gas or see signs of gas leaks, or if the boiler shows additional internal faults or lockouts beyond communication errors.
Final notes:
1) Keep a record of the error code, boiler model and serial number, thermostat model and any steps you tried — this helps the engineer diagnose faster. 2) Communication errors are often straightforward (batteries, range, pairing, loose wires) but can sometimes point to a failed receiver or PCB which require professional repair or parts replacement. Do not attempt internal repairs on the boiler yourself.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Potterton Promax Ultra, Gold/Titanium Combi & System.