Error D.93

Safety precautions:

- If you smell gas, do not operate the boiler, leave the property, ventilate where safe, and call the national gas emergency number immediately.

- Do not open the boiler casing, touch internal components, or attempt to reprogram installer menus unless you are a Gas Safe registered engineer. Incorrect settings can create unsafe conditions.

- If in doubt, isolate the boiler at the electrical isolator and call a qualified engineer.

Initial homeowner checks you can safely do:

1. Note and photograph the display showing D.93 and any other error codes; record boiler model and serial number from the data plate. This information is useful to the engineer.

2. Ask whether any recent repairs or PCB replacements were done. D.93 commonly appears after a PCB change.

3. Check the boiler has mains power and the external fused spur is on. Check the domestic electrical supply and any switched timers/thermostats are set correctly.

4. Check system water pressure on the gauge. If pressure is extremely low, top up only using the external filling loop following the boiler handbook. Low pressure is unlikely to cause D.93 but is a general operational check.

5. Try a basic reset: use the boiler reset button or switch the boiler off at the fused spur for one minute then turn it back on. If the code clears and stays cleared, monitor performance. If it returns, proceed to call a professional.

Specific diagnostic and fix steps (for the professional to perform):

- Confirm the fault: engineer will verify D.93 in the diagnostic menu and check whether the PCB is reporting an invalid or missing DSN/device-specific number.

- Check service history and parts: confirm whether the PCB has recently been replaced and whether the part number and coding resistor match the boiler model and gas type.

- Do not let homeowners enter installer menus. The correct professional procedure commonly used on Vaillant ecoTEC models is to enter installer level (D.97) with the installer code (often 17 on many models) and set the D.93 parameter to the device-specific number for that exact boiler model or apply the correct DSN offset. If a PCB swap has occurred, the engineer may instead set factory defaults (D.96) and then re-enter the correct D.93 value. These actions must only be done by a qualified engineer.

- If reprogramming is required but not possible (wrong PCB or incompatible hardware), the engineer will replace the PCB with the correct part or fit the correct coding resistor and ensure firmware/part match.

- After changing DSN or replacing components, the engineer must carry out full commissioning and safety checks: system leak/gas-tightness, flue check, combustion analysis where applicable, verify correct operation of burner and safety interlocks, and complete any local regulatory checks (e.g., Regulation 26.9 or equivalent).

- Inspect the PCB and wiring for signs of damage, water ingress or burnt components that could indicate an electrical failure rather than just configuration. Replace damaged parts as required.

When to call a professional:

- If the error persists after a safe reset, or if you know the PCB was changed recently, call a Gas Safe registered Vaillant engineer. Tell them: boiler model and serial, the exact error D.93, and whether the PCB or any repairs were done recently. If the boiler is under warranty, contact Vaillant or an authorised service agent.

Summary and emergency notes:

- D.93 is a configuration/DSN error usually related to PCB or software identification and will prevent normal operation. Homeowners can take basic non-invasive checks and a simple reset, but reassigning DSN or changing installer settings is a job for a Gas Safe qualified engineer. Do not attempt internal repairs or enter installer menus yourself. If you have any signs of gas smell or suspected unsafe condition, isolate the boiler and call the gas emergency service immediately.