Low
S.21 on Heatline Vizo 28

Your boiler is currently checking that its internal air extraction system is working correctly before it attempts to ignite the flame.

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

Pre-run fan

Shared across the range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

This is a status code, not a fault; wait for the boiler to complete its cycleMonitor the display to see if it progresses to a flame symbolIf the code persists for several minutes, try resetting the boiler

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All 111 fault codes on the Vizo 28

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

d.00d.01d.02d.08d.09d.10d.16d.17d.18d.20d.22d.23d.33d.34d.35d.36d.40d.41d.44d.67d.68d.69d.71d.80d.81d.82d.83d.85d.93d.94d.96ErrF00F01F10F11F20F22F23F24F26F27F28F29F32F49F61F62F63F64F65F67F68F70F71F72F73F74F76F77F83F84F85F86P.01P.02P.03P.05P.06P.07S.00S.01S.02S.03S.04S.05S.06S.07S.08S.10S.11S.13S.14S.15S.16S.17S.20S.23S.24S.25S.26S.27S.28S.30S.31S.32S.34S.35S.36S.37S.41S.53S.54S.58S.90S.92S.95S.96S.97S.98

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