Error E.00 – .05

Safety precautions:

1) Before doing anything, switch the boiler off at the programmer/control and isolate the mains electrical supply to the appliance at the fused spur or consumer unit. Do not open live electrical panels unless you are a qualified electrician or Gas Safe engineer. 2) Do not attempt to interfere with gas or sealed components of the boiler. 3) If you smell gas, evacuate the property and call the emergency gas number immediately.

Initial homeowner checks you can safely do:

1) Note the error code and any other messages or lights. Try a single reset using the boiler reset procedure (press and hold the reset button or follow manufacturer steps) and see if the code returns. Do not keep resetting repeatedly. 2) Check that system water pressure is normal (typically around 1–1.5 bar for most domestic systems). Low pressure can cause other faults — top up only following the manual. 3) Look around the boiler and pipework for obvious signs of water ingress, corrosion, damaged cable insulation or rodent damage to wiring. 4) Check if any recent plumbing or electrical work was done that might have disturbed wiring.

Specific diagnostic and (non-invasive) steps:

1) If you are competent and have isolated power, remove the boiler casing only if the manual allows and you are experienced; otherwise leave this to an engineer. Visually inspect the wiring that runs to the return temperature sensor: check connectors are seated, pins are not corroded and the cable sheath is intact. 2) If you have a basic multimeter and know how to use it safely with power removed, you can check continuity of the sensor cable between the sensor connector and the PCB connector. An open circuit (infinite resistance) indicates a broken wire or disconnected sensor; a near-zero resistance indicates a short. Avoid measuring resistance while the boiler is powered. 3) If the sensor connector appears to be loose or corroded, reseat it and ensure it is clipped/secured correctly, then restore power and test briefly. If the same code returns immediately, the sensor is still not communicating correctly. 4) Do not attempt to bypass the sensor or bridge terminals to force the boiler to run — that is unsafe and can cause damage or create hazardous conditions.

When to call a professional:

1) If the error persists after simple visual checks and a single reset, stop and contact a Gas Safe registered engineer. 2) Sensor replacement, wiring repair, PCB-level checks, and any internal boiler work must be carried out by a qualified engineer. Tell the engineer the exact error code (E.00 – .05), what checks you have already done, and whether the fault is constant or intermittent.

After repair:

1) The engineer will replace or rewire the return sensor or repair connectors, confirm correct operation, clear the fault, and run the boiler through heating and hot-water cycles. 2) Monitor the boiler for a few days after repair; if the code reappears, contact the engineer again.

Remember: this fault affects the boiler’s temperature sensing and safety controls. If you are not fully confident in following the safe, non-invasive checks above, call a Gas Safe engineer to diagnose and repair the fault.