S.01
FAULT CODE
Vaillant
Water Pressure Below Minimum
Low Severity
DIY Check Possible
A status (non-lockout) code indicating system pressure is approaching the minimum. The boiler is blocking but has not yet locked out.
Step-by-Step Fix Guide
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Step 1
Top up the system pressure to 1.2 bar using the filling loop
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Step 2
The boiler should restart automatically
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Step 3
If pressure drops again, check for leaks
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.