A2
Viessmann
Low System Pressure Warning
A2 warning, unit indicates low but not critical water pressure
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Gradual loss of water from system, Undersized or failed expansion vessel, Minor leaks at fittings or automatic air vents
How to Fix / Troubleshooting
Safety: Allow the system to cool before topping up. Over-pressurization can cause relief valve discharge.
- Check pressure gauge: Confirm the current system pressure. If below recommended, top up via the filling loop to 1.0–1.5 bar.
- Inspect for leaks: Look around radiators, valves, and the boiler casing for signs of dried water marks or active drips.
- Check expansion vessel: With the system depressurized, measure the air charge in the expansion vessel using a tyre gauge. Recharge to the specified pressure if low, or replace the vessel if waterlogged.
- Monitor: If pressure drops again quickly, a leak or faulty expansion vessel is likely and should be addressed by a technician.
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Repair Difficulty
Medium
3/5
Required Part
Expansion Vessel
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