Error D.81

Safety precautions:

1) If you smell gas, leave the property immediately, do not operate electrical switches, and call the gas emergency number and a Gas Safe engineer.

2) If you see water leaking from the boiler, isolate the mains electric supply to the boiler and the water supply if you can do so safely, then call an engineer.

3) Do not remove covers or attempt electrical or gas-side repairs unless you are a Gas Safe registered engineer. Internal parts (gas valve, PCB, sensors) are hazardous.

Initial homeowner checks you can do:

1) Note the display: take a photo of the D.81 message and any other codes or messages shown. Record the boiler model and serial number.

2) Check whether you have hot water and heating. If everything is working normally, D.81 is likely an informational/service log.

3) Check boiler pressure on the pressure gauge. Normal running pressure is typically around 1–1.5 bar; if below about 0.7–0.8 bar, you may need to repressurise (see your manual) but only if you are comfortable doing so.

4) Check for obvious issues: visible leaks, frozen or blocked condensate pipe (especially in cold weather), blocked flue/air intake, and that the boiler has power and the gas supply to the property is on.

5) Check timers, programmer and room thermostat settings to ensure domestic hot water is being requested.

6) Try a simple reset: switch the boiler off at the isolator or mains for 30 seconds and switch it back on. If the code clears and the boiler works normally, monitor it and book a service.

Specific diagnostic and next-step actions:

1) If D.81 is present but boiler and hot water work normally: treat it as a service/usage diagnostic. Make a note and book a routine service with a Vaillant-trained or Gas Safe engineer. Provide them the D.81 readout and any photos you took.

2) If D.81 is shown with other fault codes or if hot water/heating has failed: do not repeatedly reset the boiler. Record all codes and conditions and contact a Gas Safe engineer. Mention any accompanying codes (for example F.22, F.29, F.10 etc.)—these often indicate the real fault and will determine the engineer’s checks.

3) If water pressure is low and the boiler is showing circulation or pressure-related faults in addition to D.81: you can repressurise via the filling loop per the boiler manual, but only if you know the correct procedure. If unsure, call a professional.

4) If condensate pipe or discharge looks iced or blocked (common in cold weather) and you can safely thaw an external condensate pipe with warm (not boiling) water, do so carefully. If the condensate is blocked inside the appliance or you are not confident, call an engineer.

5) If any electrical or sensor faults are suspected (communications, NTC sensors, PCB messages): these are specialist diagnostics. The engineer will check wiring, sensor resistances, the PCB and gas/ignition components and will clear the diagnostic log as appropriate.

When to call a professional:

1) Call a Gas Safe registered engineer if D.81 appears with any loss of hot water or heating, other fault codes, leaks, unusual noises, persistent faults after reset, or if you are not certain what the code means.

2) If the code seems to be an hours/service log only, still arrange routine servicing with a Vaillant-trained or Gas Safe engineer—especially if the boiler is due a service or shows intermittent problems. Provide the engineer the boiler model, serial number and the photo of the D.81 message.

Important: Do not attempt to repair or replace gas, electrical, or sealed components yourself. Only a competent, registered engineer should work inside the appliance. If in doubt, stop and call a professional.