Error .10

Safety precautions:

1. If you are not a Gas Safe registered engineer do not attempt gas, ignition or PCB repairs. Working inside a boiler can be dangerous and may invalidate warranties.

2. Before any visual checks, turn the boiler off at the mains and isolate the electrical supply. Allow the unit to cool. Do not disconnect gas connections or attempt burner work.

3. Only perform simple, external checks and a single reset. If the fault persists, call a professional.

Initial homeowner checks (safe, non-invasive):

1. Try a controlled reset: locate the reset button on the control panel, press and hold as per the manual (usually a few seconds). If the code clears and the boiler runs normally, monitor for recurrence. Do not repeatedly reset more than once or twice.

2. Check boiler water pressure via the pressure gauge; if pressure is very low (below ~1.0 bar) top up per the manual, then try another reset. Some faults can appear alongside low pressure but NTC faults are usually separate.

3. Look for obvious signs of damage or disconnected leads on any external wiring you can see without removing the boiler casing (e.g., loose external sensor cable if fitted). Do not open the main casing if you are not qualified.

Specific diagnostic steps (for a qualified engineer or experienced technician):

1. Confirm the exact fault and event history using the boiler diagnostic menu and service mode.

2. Visually inspect NTC leads, plugs and the wiring harness for chafing, water ingress, corrosion or rodent damage. Pay attention to connectors at the flow and return sensors and at the PCB.

3. With mains isolated, disconnect the NTC sensor plug(s) and check connector pins for corrosion, bending or debris.

4. Measure sensor resistance with a multimeter at a known ambient temperature. Typical Vaillant flow/return NTCs read around 10–12 kΩ at 20°C (manufacturer variations exist). If the sensor shows near-zero ohms it indicates a short; infinite/very high resistance indicates an open circuit. Compare to expected values for the specific sensor fitted.

5. Check continuity of the wiring harness between the sensor plug and the PCB; look for shorts to earth or between conductors. Repair or replace damaged cabling as required.

6. If multiple NTCs are fitted, consider swapping flow and return sensors (or using a known-good sensor) to confirm whether the fault follows the sensor or remains at the wiring/PCB side. Vaillant guidance often recommends replacing suspected sensors to expedite diagnosis; replacing all NTCs can be helpful if sensors are ageing or multiple faults are possible.

7. If sensors and harness are good, test the PCB input for the NTC channel. A persistent erroneous input at the PCB with correct sensor readings points to a PCB fault, which requires professional attention and likely replacement by a qualified engineer.

8. After repair or replacement, restore wiring, restore mains, and clear the fault using the reset procedure. Run the boiler through heating and hot water cycles to verify correct temperature feedback and stability.

When to call a professional:

1. If the fault does not clear with the simple homeowner checks, or if you find damaged wiring, connectors, a failed sensor, or a suspected PCB issue, book a Gas Safe registered engineer.

2. Any work involving opening the boiler casing, handling gas components, replacing the PCB, or altering wiring should be performed by a qualified engineer.

3. Inform the engineer that the code is an NTC fault (F.10/.10) so they can bring the correct replacement sensors and test equipment. Vaillant documentation often recommends replacing NTCs as the first step to shorten diagnosis.

Notes:

1. Do not repeatedly reset the boiler; if the error returns, further investigation is required.

2. Replacing sensors and repairing harness wiring are common fixes. If the PCB is defective this requires a professional replacement and configuration.

3. Keep a record of the fault occurrences and any temporary fixes to help the engineer diagnose intermittent issues.