BoilerFaultCodesWhat the manual says
Manufacturer manualNo reception by the local user interface
From this model's manual
Verified against the Vaillant Ecomax Pro 28e installation & service manual, page 26.
What causes this fault?
This fault occurs when the main brain of the boiler loses its digital connection with the display panel or external controls. The most common reason is a loose or damaged internal wiring connection, though it can also be caused by an electrical component on one of the circuit boards wearing out.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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