Overview
E10 on a Baxi GA range boiler normally means the boiler has detected a fault with the outdoor temperature sensor (sometimes called an external or weather sensor). This sensor feeds the boiler controller with outside temperature so the boiler can adjust flow temperature for weather compensation. When the controller sees an open circuit, short circuit, or an implausible signal from that sensor it will flag E10 and may refuse to run in weather-compensated mode or may lock out depending on the model and how the controls are configured. Common causes are a failed sensor, damaged or corroded wiring or connector, water ingress at the external sensor, or less commonly a fault on the boiler printed circuit board (PCB) or connector inside the boiler. Severity is typically moderate: it usually does not create an immediate gas safety danger, but it can prevent normal operation, cause heating to behave incorrectly, and in some cases force the boiler to lock out. Basic checks can be done by a confident homeowner (reset the unit, check visible wiring and connector), but diagnosis beyond visual checks and simple continuity tests should be left to a Gas Safe registered engineer who can safely work on gas appliances and replace components if necessary.
Possible Cause: Outdoor sensor error
Troubleshooting Steps
Safety precautions:
1. If you are not competent working near gas or mains electricity, do not open the boiler. Call a Gas Safe registered engineer.
2. Before opening the boiler housing, switch the boiler off at the programmer/control, then isolate the mains electricity at the fused switch and, if practical, turn off the gas supply. Allow the boiler to sit for a few minutes.
3. Do not touch live electrical parts. Use insulated tools and avoid working in wet conditions. If you disconnect sensors or wiring, note connections or take photos to ensure correct reconnection.
Initial homeowner checks you can do (no special tools required):
1. Note the exact error message and when it appears (continuous, intermittent, after weather change, after power cut). Photograph the display and any wiring for the engineer.
2. Try a simple reset of the boiler per the manual (use the reset button or menu reset procedure). If the error clears and does not return, monitor the boiler for recurrence — intermittent faults can indicate a loose connector or moisture ingress.
3. Locate the outdoor sensor lead if fitted: trace the cable from the boiler to its external location. Visually inspect the cable and the sensor housing for obvious damage, kinks, crushed cable, or water corrosion.
4. Inspect the external sensor mounting position. If the sensor is sitting in very wet or flooded conditions or has visible water entry, that can cause a fault.
Specific diagnostic steps (requires basic tools like a multimeter and some electrical confidence):
1. Turn the boiler and mains power off before disconnecting any internal connectors.
2. With power isolated, open the boiler cover to the control PCB area and locate the external sensor connector (refer to the boiler wiring diagram in the manual if available). Check the connector for corrosion, bent pins, or loose wires. Re-seat the connector firmly if it looks loose.
3. Visually inspect the internal wiring for damage where the cable enters the boiler and along the route.
4. If you have a multimeter and are comfortable using it, check continuity of the sensor cable between the external sensor connector and the PCB connector. An open circuit (infinite resistance) or a short to earth/ground indicates a wiring fault or broken sensor cable.
5. If the sensor can be unplugged at both ends, measure the sensor resistance at ambient temperature. The important test is not an absolute value (sensor type varies) but that the resistance is not infinite (open circuit) and not zero (short). The resistance should change if you warm the sensor slightly (hold it between your fingers or use warm air) — a change indicates the thermistor is responding. If there is no change, the sensor is likely faulty.
6. If wiring and connector appear sound and the sensor shows appropriate resistance change, the fault could be the boiler PCB or its sensor input. Reconnect everything and try a reset. If E10 returns and you have confirmed sensor and wiring are OK, stop and call a professional.
What homeowners should not do:
1. Do not attempt to remove or replace gas valves, burners, or other gas-carrying components. Do not modify the gas supply.
2. Do not operate the boiler if you suspect a gas leak. If you smell gas, isolate the gas supply, leave the building, and call the gas emergency service immediately.
3. Avoid using makeshift bypasses or incorrect wiring fixes; these can create unsafe operation and may invalidate warranties.
When to call a professional:
1. Call a Gas Safe registered engineer if the error persists after simple resets and visible checks, or if you are not confident performing the electrical checks. The engineer can safely test sensor resistance to the manufacturer specification, check the PCB sensor input, and replace the outdoor sensor, lead, or PCB if required.
2. If the wiring inside the boiler is damaged or if the fault is intermittent and cannot be traced by visual inspection, get a professional to prevent recurring faults and ensure safe operation.
Documentation for the engineer:
1. When you call an engineer, give the boiler model and serial number, describe when E10 appears, and tell them what checks you have already carried out (reset, visual inspection, any meter readings). Provide photos of the sensor, cable entry points, and the PCB connector if possible. This will speed diagnosis and repair.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi GA Range.