ACV Thermostat 54764033

This is a mechanical overheat safety thermostat with a bulb-type sensing element. It is designed for ACV HeatMaster 100 and HeatMaster 120 boilers. The bulb has a diameter of 6 mm, and the capillary tube is 3000 mm long. It operates mechanically to respond directly to temperature changes and acts as a safety cut-out that prevents overheating of the heat exchanger.

Parts of this type are selected by the switching temperature, reset mode (manual or automatic), and switching function (normally open or normally closed). The sensing element must match the installation point: immersion bulbs require a thermal well, clamp-on probes need good contact and thermal paste, and capillary thermostats must have enough bulb length and capillary reach. Before ordering, compare the capillary length and bulb diameter with the original part, and verify that the electrical rating matches the burner control circuit.

When a mechanical overheat thermostat fails, the burner may lock out, fail to start, or cycle erratically. A drifting set point can allow the heat exchanger to overheat before the safety cut-out opens, while loss of capillary charge or poor thermal contact may result in delayed switching or no switch at all. Check the capillary and bulb for damage and verify that the clamping area is clean and thermally coupled to the pipe.