A pressure clamp adapter for mounting a thermistor on an existing thermostat control support bracket secured to a hot water tank spud is described. It comprises a thermistor bracket having a rear wall with opposed transverse projecting connecting arm formations extending from an outer surface of the rear wall. A cavity is formed from the rear surface of the rear wall to form a housing shaped to receive a thermistor therein. A passage communicates with the cavity. Each of the connecting arm formations is adapted for removable attachment to a pair of upwardly projecting legs of the thermostat control support bracket.