Error E5 218

Safety precautions:

1) If you smell gas, do not touch the boiler. Evacuate the property, call the gas emergency number and a Gas Safe engineer. Do not attempt internal repairs on gas components unless you are Gas Safe registered.

2) Turn the boiler off and isolate electrical supply before carrying out any physical checks. Allow the system to cool before touching pipes or components.

3) If the boiler has been overheating, allow it to cool fully before attempting resets or inspections to avoid scalding.

Initial homeowner checks (safe, simple checks you can do yourself):

1) Note the error exactly (E5 218) and the circumstances (when it appears — on CH demand, DHW, immediately after reset).

2) Try a boiler reset using the control panel reset function. Wait for a full restart cycle and see if the fault returns. If it clears and does not return, still arrange a service to find the root cause.

3) Check system pressure on the gauge. Normal cold pressure is typically around 1–1.5 bar. Very low pressure can cause circulation problems; very high pressure can indicate other issues. Do not repressurise if you are unsure — consult your manual or an engineer.

4) Check that radiators and TRVs are open and that any motorised zone valves are in the correct position. If only some radiators are cold, bleed them to remove airlocks.

5) Listen for the pump running when there is a heating demand. If you cannot hear or feel the pump running, circulation may be compromised.

6) Check for visible leaks, blocked condensate outlets, or frozen condensate pipes (in winter) which could cause related faults.

Specific diagnostic steps and fixes (some require an engineer):

1) If the error persists after a reset, do not continue to cycle the boiler repeatedly. Record when the fault occurs and any patterns to give to the engineer.

2) Visual inspection: with the power isolated, check the flow sensor wiring and connector for signs of damage, corrosion or a loose plug. Re-seating a connector can sometimes clear a fault if you are able and comfortable to do so; ensure power is off first.

3) Bleed radiators and remove airlocks that can reduce flow and cause rapid temperature rises in the flow pipe.

4) Check the pump is operating correctly. If the pump is seized, set too low, or has failed, it will reduce circulation and can cause the flow temperature to spike. Pump fault diagnosis and replacement is a job for a competent engineer.

5) Limescale and debris: a build-up of scale in the flow sensor pocket or on the heat exchanger can make sensors read incorrectly or reduce heat transfer. An engineer can inspect the sensor, remove scale, fit an in-line scale reducer, or recommend a chemical powerflush if the system is contaminated.

6) Sensor test and replacement (engineer): the flow temperature sensor (NTC thermistor) is tested with a multimeter to check resistance versus temperature against manufacturer specifications. If out of tolerance or physically damaged, the sensor should be replaced. This requires isolating electrical supply and access to the sensor pocket and wiring.

7) Control board and other sensors: if wiring and the sensor are good, the PCB or related electronics may be faulty. A trained engineer will test the control board and related temperature sensors (flow, return, safety sensor) and replace the faulty module if required.

8) Heat exchanger and valves: if circulation and sensors are OK, the cause may be a blocked heat exchanger, faulty three-port/diverter valve, or other hydraulic fault. These need an engineer to diagnose and repair.

Actions after a repair:

1) After any repair or replacement, the engineer should clear the fault, run the boiler through heating and hot water cycles, and confirm stable operation without the error returning.

2) Keep a record of the fault and any parts fitted; arrange a full service if you haven’t had one in the last 12 months.

When to call a professional:

1) If the fault does not clear after a simple reset and the basic checks above, call a Gas Safe registered heating engineer. Do not attempt to test or replace gas or sealed electrical components yourself.

2) Call an engineer promptly if you suspect pump failure, wiring damage, a permanently high temperature reading, repeated lockouts, visible leaks, or any signs of unsafe operation. The error protects the boiler, but ongoing overheating or faulty sensing can cause further damage if not fixed.

Summary: start with a safe reset and basic circulation checks, bleeding radiators and confirming pump/valves and pressure. If the code returns, or if any wiring, sensor or pump work is required, stop and book a Gas Safe engineer to carry out multimeter diagnostics, sensor replacement, hydraulic cleaning or PCB work. Do not attempt gas or advanced electrical repairs yourself.