Error E28

Safety precautions:

- Do not attempt to repair gas or sealed combustion parts unless you are a qualified Gas‑Safe engineer.

- Isolate the electrical supply to the boiler at the mains switch before removing any covers. If you suspect a gas leak or smell gas, turn off the gas supply at the meter, ventilate the area and call the gas emergency number immediately.

- Wear eye protection and use insulated tools if you are carrying out visual checks. If in doubt, stop and call a professional.

Initial homeowner checks (safe, non‑invasive):

1) Note the exact fault code(s) and any behaviour (e.g. boiler tries to fire then locks out, steady lockout). Record model and serial if available.

2) Simple reset: switch the boiler off at the mains, wait 30 seconds, then switch back on. Some sensor errors clear if transient; if E28 returns immediately or repeatedly, further action is needed.

3) Inspect the external flue terminal (outside the property): check for obvious blockages (nests, leaves, soot buildup) or damage. Carefully clear visible debris from the terminal but do not insert objects into the flue.

4) Check boiler front display for any related codes (E130/E131 indicate flue thermostat trips/lockout) and check system pressure on the gauge—repressurise only if the pressure is low and you know how to do so safely.

Basic diagnostic steps (what a competent homeowner may do, still without internal repairs):

- With power off, check any easily accessible wiring and plug connections at the boiler front for signs of loose connectors, corrosion, or a disconnected lead. Do not probe live circuits.

- If the flue terminal was blocked and you cleared it, reset the boiler and observe. If the code clears and operation is normal, monitor for reoccurrence.

When to call a professional (and what they will do):

- If E28 persists after a reset and clearing the flue terminal, or if you are not comfortable opening the boiler case, call a Gas‑Safe registered heating engineer.

- A qualified engineer will isolate and safely open the boiler, inspect and test the flue thermistor and its wiring, measure NTC resistance behavior, check connectors and the harness for condensate damage, and confirm the flue path is clear and the flue thermostat has not latched into lockout. They will also test related components and the PCB to ensure the fault is not an electronic error.

- If the thermistor is faulty they will replace it, re‑test the system, and perform any necessary combustion and safety checks. If there is evidence of flue obstruction or poor flue performance they will investigate the flue run and terminal, and may need to carry out further remedial work.

Important reminders:

- Do not bypass safety devices or try to force the boiler to run while a safety fault code is displayed.

- Any internal work, sensor replacement, or diagnostics requiring electrical measurements, gas adjustments, or combustion testing must be done by a Gas‑Safe registered engineer. Persistent or intermittent E28 faults often require professional diagnosis to ensure safe, correct repair.