How much does it cost to fix Biasi error code E21?

Typical repair cost for the Biasi E21 fault is £80-140 including labour.

E21 High

Biasi E21 Fault Code

Q: What does the Biasi E21 fault code mean?

Your boiler has shut down because the waste water pipe that carries away condensation is blocked or frozen, causing water to back up into the unit.

The Biasi E21 fault code means: your boiler has shut down because the waste water pipe that carries away condensation is blocked or frozen, causing water to back up into the unit.. It appears on 6 Biasi models in our database.

Technical description: Condensate trap blockage or drain pipe obstruction

Typical repair cost £80-140 (including labour)

DIY fix possible

Locate the plastic white pipe exiting the wall outside your property.If the weather is freezing, pour warm (not boiling) water over the external pipe to melt any ice blockages.Check that the end of the pipe is not submerged in water or blocked by debris.Reset the boiler using the control knob to see if the error clears.

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Biasi models that show the E21 fault code

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

Source

Biasi E21 fault code information on this page is sourced and cross-checked against the official Biasi service / installation manuals for each affected model.

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