BoilerFaultCodesVaillant F.83 Fault Code
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 19 Vaillant models in our database.
Technical description: Fault: Dry fire When the burner starts, the temperature change recorded by the flow or return temperature sensor is non-existent or too small: Insufficient water in the product, flow or return temperature sensor incorrectly attached to the pipe
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.
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
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Vaillant models that show the F.83 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £90-180
- ecoFIT Pure 412 Repair: £150-250
- ecoFIT Pure 418 Repair: £120-250
- ecoFIT Pure 425 Repair: £120-250
- ecoFIT Pure 435 Repair: £120-250
- ecoFIT Pure 825 Repair: £150-300
- ecoFIT Pure 830 Repair: £150-250
- ecoFIT Pure 835 Repair: £150-250
- ecoTEC exclusive Repair: £120-250
- ecoTEC Plus 610 Repair: £120-250
- ecoTEC Plus 826 Repair: £150-250
- ecoTEC Plus 938 Repair: £100-250
- ecoTEC Pro Repair: £100-£220
- ecoTEC Pro 24 Repair: £100-£220
- ecoTEC Pro 28 Repair: £100-£220
- ecoTEC Pro 30 Repair: £120-250
- ecoTEC sustain Repair: £100-250
- Home Combi Repair: £150-300
- Home System Repair: £100-220
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.
- Vaillant ecoFIT Pure 412 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant ecoTEC exclusive manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026