Low
F.668 on Viessmann Vitodens 200-W B2HE-19

Your boiler has noticed a problem with a temperature sensor that controls how the water tank is pre-heated by solar energy, so it may not be using that extra free heat, but your boiler can still heat your water and home.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

Preheating of second DHW cylinder and solar transfer pump not working - Lead break, temperature sensor, DHW reheating TS4

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 100 W Wb1a installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.667View →F.669View →

All 170 fault codes on the Vitodens 200-W B2HE-19

Seeing a different code? Every code this model can display, in one place.

F.7F.8F.9F.10F.11F.12F.13F.14F.15F.16F.29F.30F.49F.50F.57F.58F.59F.62F.63F.65F.67F.68F.69F.70F.71F.72F.73F.74F.77F.89F.91F.92F.93F.94F.100F.104F.142F.160F.161F.162F.163F.182F.183F.184F.185F.299F.342F.345F.346F.348F.349F.350F.351F.352F.353F.354F.355F.357F.359F.361F.365F.366F.367F.368F.369F.370F.372F.373F.375F.377F.378F.380F.381F.382F.383F.384F.385F.386F.387F.388F.395F.396F.399F.400F.401F.402F.403F.404F.405F.406F.408F.410F.416F.417F.418F.425F.426F.427F.428F.429F.430F.432F.433F.436F.437F.440F.441F.442F.443F.444F.445F.446F.447F.448F.449F.450F.451F.452F.453F.454F.455F.456F.457F.458F.461F.462F.463F.464F.467F.468F.471F.473F.474F.517F.527F.528F.530F.538F.539F.540F.542F.543F.544F.545F.546F.547F.574F.575F.576F.577F.578F.579F.580F.581F.582F.666F.667F.669F.670F.671F.672F.673F.682F.683F.684I.55I.56I.57I.59

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