F6
FAULT CODE
Viessmann
Low Water Pressure
Low Severity
DIY Check Possible
The system water pressure has dropped below the minimum safe level. The boiler cannot circulate water safely.
Cold Weather Note
Pressure drops can be more frequent in cold weather as the system contracts.
Step-by-Step Fix Guide
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Step 1
Check the pressure gauge on the boiler — it should read between 1.0 and 1.5 bar
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Step 2
Locate the filling loop (usually beneath the boiler) and slowly open the valves
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Step 3
Fill until the gauge reads 1.2 bar, then close both valves
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Step 4
Reset the boiler
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Step 5
If pressure drops again within a few days, there may be a leak in the system
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.