Error E28

Safety precautions:

1) If you smell gas or suspect a gas leak, leave the property immediately and call the emergency gas service. Do not attempt any checks. 2) Before touching the boiler internals or wiring, switch the boiler off at the programmer and use the electrical isolator or fuse to remove mains power. Never work on live electrical circuits or on the combustion chamber unless you are qualified. 3) Do not attempt to modify or repair gas valves, ignition components, or the combustion chamber yourself — these require a Gas Safe engineer.

Initial homeowner checks you can do safely:

1) Note the exact error code and any LEDs or additional messages on the display. Take a photo if needed. 2) Try a simple reset: switch the boiler off, isolate power for 30 seconds, then restore power and see if the fault clears. Do not repeatedly reset if the fault returns immediately. 3) Check the flue terminal outside for obvious blockages (bird nest, leaves, debris) and remove only external obstructions if safe to do so from ground level. 4) Check the boiler pressure on the gauge; while not directly the flue thermistor, low system pressure or circulation faults can cause other faults—top up to the recommended pressure if it is low and you know how to do so safely. 5) Confirm other gas appliances work (e.g., hob) to rule out a supply interruption — do not try to relight pilots or tamper with gas appliances.

More detailed diagnostic steps (for competent DIYers only) and what to expect:

1) Visual inspection: with power isolated, remove the boiler casing only if you are comfortable doing so and can do it safely. Look for obvious signs of damage to the flue thermistor wiring or its connector (corrosion, water ingress, pin damage, burnt wiring). Also look for signs of soot, condensation pooling or damage around the flue sensor area. If you are unsure, stop and call a professional.

2) Reseat connectors: with power off, carefully disconnect and reconnect the sensor connector to ensure a tight connection. Corroded or loose pins can cause intermittent faults.

3) Continuity/resistance check: if you have a multimeter and are competent using it, isolate power and disconnect the thermistor plug, then measure resistance across the sensor. If the reading is open circuit (infinite) or a near-zero short, the sensor is faulty. Exact resistance vs temperature depends on the sensor type and the boiler manual; if you are not confident interpreting results, leave this to an engineer. Do not apply power to the circuit while probing live connectors.

4) If the sensor appears intact but the fault persists after reseating and resetting, check the wiring harness for intermittent breaks along accessible runs. Intermittent faults can be caused by chafing or water tracks into the connector.

5) Flue obstruction check: if you found and cleared an external blockage, reset the boiler and observe whether the E28 clears. If the flue was blocked, the sensor may have been exposed to abnormal temperatures or contamination and could still be faulty.

When to call a professional and next steps for the engineer:

1) If the simple reset and external checks do not clear E28, or if your continuity/resistance checks show an open or short, call a Gas Safe registered engineer to replace the thermistor and inspect the flue and wiring. 2) Any work that requires accessing the combustion chamber, replacing the sensor, adjusting or testing gas and ignition components, or interfacing with the PCB must be done by a qualified engineer. 3) If the E28 returns after sensor replacement, the engineer will investigate related items such as the PCB, wiring looms, fan operation, or flue thermostat/overheat devices.

Final notes:

Do not repeatedly reset the boiler to force operation — repeated lockouts can indicate a safety issue. Document the fault occurrences, any steps you took, and the boiler model and serial number before the engineer arrives to speed diagnosis. For safety and compliance always use a Gas Safe registered engineer for repairs or replacement of sensors and any work involving gas or combustion components.