The booster did not cook the machines. They were 600 watts and raised the water temperature one degree per minute. The tubs were not insulated in the earlier WH built in machines so Westinghouse came up with the idea of heating the circulating water. Youngstown Jet Tower and Apex had little uninsulated water tanks that heated the water for the machine, but once it hit the cold dishes, it cooled. At this time, WH did not have a detergent dispenser so the hot water for the main wash hit the cold tank and dishes because the machines could not have a pre-rinse to warm up the machine and the load. The washing cycle was extended until 140F was reached if the booster was turned on and only the Top of the Line model in this series had the switch for the booster. The portable model under it did not have the hot water booster feature. It probably ran the heater for the duration of the wash, with no thermal hold; at least that is what the salesman at Davison's told us. Steve D. can confirm.
The vulnerable point on these WH DWs was the plastic control panel which did not contain a fire if one started in the controls.