Error D.97

Safety precautions:

1) If you smell gas, evacuate the property immediately, do not operate electrical switches or the boiler, and call the gas emergency number and a Gas Safe engineer. 2) If you see liquid coming from the condensate or any obvious water leak, isolate the boiler’s electrical supply and turn off the water feed to the heating system if you can do so safely; then call an engineer. 3) Do not open the boiler cover, do not alter wiring, and do not change D‑menu parameters unless you are a qualified installer. 4) Keep a CO alarm in the property and follow manufacturer safety instructions on the boiler casing.

Initial homeowner checks you can do (safe, non‑invasive):

1) Note the exact display message and any other F‑codes shown alongside D.97. Take a photo of the screen. 2) Check if heating and/or hot water are working. If everything functions normally, D.97 may just be the display mode and you can try the simple exit steps below. 3) Check the boiler pressure gauge—typical normal operating pressure is 1.0–1.5 bar when cold. If the pressure is very low (<0.5 bar) or very high (>2.5 bar), do not attempt settings changes beyond repressurising with the filling loop per the manual; low/high pressure can cause the boiler to lock out. 4) Check household power (fuse/rcd/trip) and ensure the boiler has mains power.

Safe attempts to exit diagnostic mode and restore normal operation:

1) Simple exit: Try pressing and holding the same buttons used to enter diagnostics (often the i/info button and the + or -). If you remember how you entered it, repeat the same press combination to exit. If unsure, press the back/return button or the main information button to cycle back to the normal display. 2) Soft reset: Use the boiler’s reset button (if fitted) as the manual instructs. Press once and wait to see if normal operation resumes. 3) Power cycle: Switch the boiler off at the room thermostat and the boiler’s on/off switch or at the fused spur, leave off for 60 seconds, then restore power. This will exit diagnostic modes in most cases. 4) After exit, observe the boiler for correct ignition, normal pump sounds, and that heating/hot water requests are satisfied. Recheck pressure.

If those steps do not clear D.97 or the boiler fails to run normally:

1) Do not try to change D‑menu settings yourself. D‑parameters control burner output, range rating and safety setpoints; incorrect changes can cause poor performance or unsafe operation. 2) Record any accompanying F‑codes and symptoms (no ignition, repeated lockouts, unusual noises, pressure faults, etc.). 3) Contact a Gas Safe registered heating engineer or Vaillant customer support. Provide them with the display readout, photos, and the steps you have already taken. 4) If the boiler has recently been worked on by an installer, contact them — they may have left it in a diagnostic mode intentionally.

What the engineer will typically check (for your awareness):

1) Exit/restore settings and confirm the boiler is not left in installer mode. 2) Read diagnostic parameters and log values (flow temperature, return, pressure, pump speed, flame signal etc.) to identify any abnormal measurements. 3) Check sensors, wiring harness, and the PCB for faults if abnormal readings are present. 4) If a true fault is found, the qualified engineer will make repairs or replace components and test the boiler safety and operation.

Final note: D.97 itself is informational and usually not an emergency, but if the boiler won’t return to normal service after a power cycle/reset, or if you see other error codes, abnormal pressures, loss of gas supply or safety concerns, arrange an inspection by a Gas Safe engineer. Do not make changes in the diagnostic/installer menus unless you are a trained installer.