Furnace shows H2; may shut down on high pressure

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.

Possible Causes

Overfilled system, Faulty expansion vessel (no air charge), Stuck fill valve, Blocked expansion line

Safety: Let the system cool. High pressure combined with high temperature is dangerous.

Check gauge: If pressure is above the recommended maximum (often ~2.5–3 bar), reduce it.
Relieve pressure: Bleed water from a radiator or drain point into a container until pressure returns to normal.
Check filling loop: Ensure the filling valve is fully closed and not leaking by.

If pressure rises again during operation, the expansion vessel may be waterlogged and needs service or replacement by a professional.

Medium 3/5

Expansion Vessel

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