E08
De Dietrich
Expansion Vessel / Pressure Regulation Fault
Boiler displays E08, expansion vessel / pressure fluctuation fault
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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
Failed expansion vessel diaphragm on De Dietrich boiler, Loss of air charge in vessel, Blocked connection between vessel and system, Oversized or undersized vessel for installation
How to Fix / Troubleshooting
Safety: Allow the system to cool. Hot water under pressure can be dangerous.
Steps:
- Observe pressure behaviour: If pressure rises rapidly when heating and then discharges via the safety valve, the expansion vessel may be faulty.
- Check vessel charge (qualified persons): Isolate the boiler, drain pressure to zero, and measure the air charge at the Schrader valve on the vessel. It should match the specified pre‑charge (often around 0.8–1.0 bar). Re‑pressurise with a pump if low.
- Inspect for leaks: If water comes out of the Schrader valve, the diaphragm is ruptured and the vessel must be replaced.
Professional help: Expansion vessel replacement or adding an external vessel should be done by a heating technician.
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Repair Difficulty
Hard
4/5
Required Part
Expansion Vessel
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