Error D.93

Safety precautions:

- If you smell gas, leave the property immediately and call the gas emergency line. Do not operate electrical switches or the boiler.

- Do not open the boiler casing or touch internal components. Isolation of mains electrical and gas isolation must only be done by a qualified engineer.

- Take photographs of the display and any labels before attempting resets so an engineer has full information.

Initial checks a homeowner can do:

1) Note recent events. Did the fault appear after servicing, a PCB change, power cut, or part replacement? D.93 often follows PCB replacement or incorrect part coding.

2) Record the exact display messages and any additional fault codes (for example F.70 or F.83 might appear alongside). Take a photo of the control panel.

3) Try a basic power reset: switch the boiler off at its room thermostat and at the mains, wait 30 seconds, then switch mains back on and clear/reset any displayed fault using the reset button. Observe whether D.93 returns.

4) Check that the boiler has mains power and that any external controls or timers are calling for heat; sometimes configuration faults appear only when a demand is present.

Specific diagnostic and fix steps (for an engineer or technician):

- Understand the cause: D.93 indicates the DSN/appliance variant setting is incorrect or not set. This is often fixed by entering the installer/diagnostic menu and setting the correct DSN offset for the specific boiler model or by assigning the correct software identification to the PCB.

- Recommended approach used by engineers: access the installer diagnostics menu and check the DSN/variant settings. Common procedure includes entering the installer level, going to D97 and entering the level code (for some older EcoTEC units this is 17), then selecting D93 to view/change the DSN offset and entering the correct value from the manufacturer DSN table for that boiler model. After changing, accept the value and perform a reset. If that does not resolve it, some systems allow a factory defaults reset via D96 set to 1 and then reset, but only if advised by manufacturer guidance.

- Always record the original settings before making any changes. If the wrong DSN is entered the boiler may behave incorrectly; only set the value matched to the exact boiler model and parts combination.

- If DSN cannot be programmed or the fault persists after correct DSN entry, further electronic diagnostics are required. This may include verifying the PCB is correct for the model, checking the coding resistor and wiring harness, confirming sensor plugs and harnesses are correctly connected, and testing for communication faults between the user interface and main PCB.

When to call a professional:

- If the basic power reset does not clear the code, or if you suspect a PCB or configuration change caused the fault, call a Gas Safe registered engineer or Vaillant-authorised service agent. Programming DSN values, replacing or testing the PCB, and any internal electrical or gas component work must be done by a qualified engineer.

- Provide the engineer with photos of the fault display, the boiler model and serial number, and any recent service history or parts changes to speed diagnosis.

Final note: Do not attempt internal repairs, PCB swaps, wiring or gas adjustments yourself. Incorrect configuration or unsafe repairs can create dangerous conditions and will void warranties. A qualified engineer will have the correct DSN table, access codes, and tools to restore the boiler to safe operation.