Error D.47

Safety precautions:

- If you smell gas, leave the property immediately and call the gas emergency number (in the UK: 0800 111 999). Do not operate electrical switches.

- Switch the boiler off at the electrical isolator before inspecting electrical connections.

- Do not open the boiler casing or work on gas components unless you are qualified.

- If in doubt, stop and call a Gas Safe registered engineer.

Initial checks a homeowner can do:

1. Record the exact message on the display and take a photo of the code and the boiler display. This helps later diagnosis.

2. Check whether an external outside temperature sensor is actually fitted to the property. Look for a small probe or junction box on an external wall connected by a thin cable to the boiler. If there is no sensor fitted and the controller is configured to use one, the controller will report a weather-compensation error.

3. Visually inspect the sensor and cable for obvious damage, cuts, loose connections or water ingress at the sensor head or at any external junction box.

4. Restart the boiler: use the normal reset method (e.g. press and hold the power button for ~5 seconds) and see if the D.47 returns. Note: do not repeatedly reset if the fault persists; record it for the engineer.

Specific diagnostic and DIY troubleshooting steps:

1. Disable weather compensation temporarily (if you have a Vaillant controller and cannot get the sensor working) to restore normal control:

- Access the installer/settings menu on the boiler/controller (only if you are comfortable doing so). On some EcoTEC Plus units the weather-compensation control can be switched off in the diagnostic/installer settings (video transcripts and installer manuals reference a D162 setting controlling weather compensation). Deactivating that setting will stop the boiler looking for the outside sensor and should allow normal heating control. Caution: changing installer settings can affect performance; only do this as a temporary measure.

2. Inspect the connector at the boiler: with the boiler isolated from mains power, check the sensor cable termination at the boiler wiring block for secure connection and no corrosion. Re-seat connectors if accessible and intact.

3. If you have a multimeter and are competent using it: with the sensor disconnected, measure continuity to verify the cable is intact. If the sensor is a two-wire NTC thermistor (common), you can measure resistance and check it changes when warmed (hold gently in your hand) — resistance should change noticeably with temperature. If the sensor reads open circuit (infinite resistance) or short circuit, it is faulty and needs replacement. Exact resistance values vary by sensor model so use the change in resistance as the check rather than a specific number.

4. If the sensor appears present and the wiring looks sound but the code persists, re-check controller wiring and any intermediary junction boxes. Corroded joints or water entry are common failure points on external sensors.

5. If the sensor is missing, damaged or fails the electrical checks, the proper fix is to replace the outside temperature sensor with the correct Vaillant part and have it wired and tested by a competent installer.

When to call a professional:

- If you are not comfortable accessing installer menus, working with electrical measurements, or accessing the boiler wiring.

- If the sensor wiring is damaged, the sensor needs replacing, or the fault persists after the simple checks above.

- Any work involving opening the boiler, gas components, or mains electrical parts must be carried out by a Gas Safe registered engineer (or equivalent competent person).

Notes and recommendations:

- Disabling weather compensation is a temporary workaround to restore heating control; long-term you should repair or replace the outside sensor so the system can operate efficiently.

- Keep a record of any diagnostic steps you took and photos of wiring or faults to give to the engineer.

- If you need a service/repair, book a Gas Safe registered engineer and provide them with the error code (D.47), the boiler model, and details of any steps you have already taken.