If the aux coolant pump went bad you'd still have heat. The pump only runs at idle to help flow. Try testing the heater monovalve by unplugging the electrical connector- this causes it to open.

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Streetside: 1987 Mercedes 300E Petrol Blue/Green
2014 Ford Mustang Grabber Blue
1999 Ford Ranger Green

Dockside: 1968 Eltro 17
1985 Silverton 34C