Is the water geting into the tank from the vent (overhanging pipe) or from the feed (bottom of tank). If the latter thats a symptom of cylinder coil problem. If its that former its pumping over. If pump on setting 3 turn it down to 2 and see what happens. Could be a blockage. Usual place is where the feed pipe joins the primary circuit.
In any event I think you need to get someone in to look at it for you.
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