Error E84

Safety first: If you smell gas or suspect a gas leak, leave the property immediately and call the national gas emergency number. If you are not comfortable working near electrical equipment, do not attempt internal checks. Do not open the boiler casing or attempt internal repairs unless you are a registered engineer. Only perform external and non-intrusive checks.

Initial checks a homeowner can do:

1) Note the exact code and whether any other codes are shown, and when the fault started.

2) Try a simple reset: press and hold the boiler reset button for 5–10 seconds (or switch the boiler off at the isolator, wait 30 seconds and turn it back on). If the error clears and does not return, it was likely a temporary glitch.

3) Check mains power: confirm the boiler display/clock is powered and check the consumer unit for tripped breakers or blown fuses.

4) Check your room thermostat or programmer: set the thermostat higher than room temperature to force a call for heat and see if the boiler responds. For wireless thermostats, replace batteries and check the thermostat display. For wired thermostats, confirm the thermostat is powered and calling for heat (if you are unsure how, try changing settings to trigger heating).

5) For wireless systems check that the thermostat and receiver are within range and free from large metal obstructions or devices that can cause interference. If the thermostat and receiver can be re-paired by following the manufacturer instructions, try re-pairing.

6) Visually inspect any external wiring you can safely access (thermostat wiring, external timers). Look for obvious damage or loose terminals. Important: isolate electrical supply to the boiler before touching terminals or wires; if you are not confident, stop and call an engineer.

7) Check boiler water pressure as a general health check (aim for about 1–1.5 bar). E84 is a communication fault, but low pressure can cause other faults to appear.

Specific diagnostic and next-step fixes:

1) If reset cleared the fault but it returns intermittently, replace thermostat batteries (if wireless) and monitor. Intermittent E84 often points to wireless battery/range or a loose connection.

2) If wired thermostat and you are competent with simple electrical isolation: switch off electricity to the boiler, open the thermostat and visually check the call-for-heat wires are secure. Restore power and test. If you see damaged cable or are unsure, stop and call an engineer.

3) For wireless systems, attempt a full re-pair of thermostat and receiver according to the manufacturer's instructions. Move the thermostat temporarily closer to the boiler/receiver to rule out range issues.

4) If the boiler shows additional fault codes alongside E84, write them down — they help the engineer diagnose the root cause.

5) If you have completed the above and the E84 persists (or if you had to open the boiler, if other faults appear, or if the boiler repeatedly locks out), call a Gas Safe-registered heating engineer. Likely professional interventions include testing and replacing the wireless receiver or thermostat, repairing/replacing damaged control wiring, or diagnosing and replacing a faulty PCB or internal module. These tasks require specialist tools and gas/electrical qualifications.

When to call a professional immediately: the error does not clear after a reset and basic checks, the fault keeps recurring, you find damaged internal wiring, you smell gas, or you are unsure about any step. Do not keep repeatedly resetting the boiler; repeated lockouts indicate a persistent fault that needs a qualified engineer. Provide the engineer with the exact error code (E84), any other displayed codes, and the checks you have already carried out to speed up diagnosis.