How much does it cost to fix Saunier Duval error code 1 then 2?

Typical repair cost for the Saunier Duval 1 then 2 fault is £80-120 including labour.

1 then 2 High

Saunier Duval 1 then 2 Fault Code

Q: What does the Saunier Duval 1 then 2 fault code mean?

Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.

Also written as 1THEN2 — same fault.

The Saunier Duval 1 then 2 fault code means: your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.. It appears on 2 Saunier Duval models in our database.

Technical description: The appliance will shut down if the pressure gauge indicates a loss of system pressure, i.e. less than 0.7bar.

Typical repair cost £80-120 (including labour)

DIY fix possible

Locate the filling loop (usually a silver braided hose with one or two valves) under your boiler.Gradually open the valve(s) to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valve(s) tightly and reset the boiler to clear the error code.

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Saunier Duval models that show the 1 then 2 fault code

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

Source

Saunier Duval 1 then 2 fault code information on this page is sourced and cross-checked against the official Saunier Duval service / installation manuals for each affected model.

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