How much does it cost to fix Vaillant error code F.83?

Typical repair cost for the Vaillant F.83 fault is £100-250 including labour.

F.83 High

Vaillant F.83 Fault Code

Q: What does the Vaillant F.83 fault code mean?

Your boiler is firing up, but it doesn't detect the water getting hotter quickly enough, so it has shut down to prevent itself from overheating.

Also written as F83 — same fault.

The Vaillant F.83 fault code means: your boiler is firing up, but it doesn't detect the water getting hotter quickly enough, so it has shut down to prevent itself from overheating.. It appears on 34 Vaillant models in our database.

Technical description: Dry fire - Flow/return temperature sensor change too small

What causes the Vaillant F.83 fault?

This fault occurs when the boiler's internal computer registers that the burners are on, but the temperature sensors fail to detect a significant rise in heat within the water. The most common reason is a lack of water circulating through the system, often caused by a pump failure, a blockage, or even just too much air trapped in the pipework. Because the boiler cannot move the heat away from the burner quickly enough, it shuts down to prevent 'dry firing' and damaging the internal components.

This fault is more frequent in autumn when the heating is turned on for the first time after summer, as circulation pumps are prone to seizing or sticking after long periods of inactivity.

Typical repair cost £100-250 (including labour)

DIY fix possible

Check that your boiler pressure is between 1.0 and 1.5 bar on the digital displayEnsure all radiator valves (TRVs) are turned to the highest settingTop up the water pressure using the filling loop if it is too low

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Vaillant models that show the F.83 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant F.83 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026