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BoilerCodes
F.83Vaillant

Vaillant F.83: no temperature change detected when the burner started

Checked against Vaillant's own documentation: Vaillant ecoTEC plus installation and maintenance instructions: overview of fault codes (continued) and 2 more sources. Last reviewed October 2026. How we check

Check these first, then call an engineer

When the burner lights, the boiler expects the water temperature to rise. It saw little or no change, so it stopped. Vaillant lists too little water in the boiler, or a temperature sensor out of position on its pipe, as causes.

Recommended pressure when cold for Vaillant boilers: 1.0 to 2.0 bar.

What you can safely do

  1. Read the pressure gauge with the system cold. If it is below 1.0 bar, top it up to between 1.0 and 2.0 bar as you would for F.22.

Call a Gas Safe engineer if

  • The pressure is already between 1.0 and 2.0 bar.
  • F.83 comes back after topping up.
Find a Gas Safe engineer near you Opens the official Gas Safe Register search.

Applies to ecoTEC plus. Codes can differ between models, so check your manual.

What F.83 means on each Vaillant model

From Vaillant's own fault tables. Your model name is usually on the front of the boiler or in the user manual.

ModelMeaningCauses listed for engineers
ecoTEC plusFlow and/or return temperature sensor temperature change faultWhen the burner starts, the temperature change at the flow or return sensor is non-existent or too small: insufficient water in the boiler, or a sensor not correctly positioned on its pipe

Common questions about Vaillant F.83

Can I fix F.83 myself?

Only the pressure check. Low water is one cause Vaillant lists. If the pressure is fine, a sensor needs checking by an engineer.

Is F.83 the same on Glow-worm boilers?

Glow-worm, part of the same group, lists the same temperature-change fault under F.83, but its fault table also shows a second, different F.83 meaning. Check your own manual.

Nearby Vaillant codes

See all 36 Vaillant codes

Sources

Last reviewed October 2026. Spotted something that doesn't match your manual? Email hello@boilercodes.co.uk and we'll check it. How we check