60:20 Medium

Viessmann 60:20 Fault Code

Also written as 6020 — same fault.

The Viessmann 60:20 fault code means: your boiler is getting too hot while trying to heat your water, which usually means the heat isn't being transferred to your hot water tank quickly enough.. It appears on 5 Viessmann models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: During DHW loading, the boiler water temperature is max. 20K higher than set DHW temperature

What causes the Viessmann 60:20 fault?

This fault occurs when the water inside the boiler gets much hotter than the water in your tank, suggesting that heat is trapped and cannot circulate properly. The most common reason is a blockage or limescale buildup in the heat exchanger, or a failing diverter valve that is stuck and preventing the flow of hot water to your cylinder.

Typical repair cost £120-£350 (including labour)

Engineer required

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

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Viessmann models that show the 60:20 fault code

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

Source

Viessmann 60:20 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

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