ACV Thermostat with manual or automatic reset, featuring a capillary 54764006

ACV Thermostat with manual or automatic reset, featuring a capillary bulb for remote temperature sensing. It is designed for use in HeatMaster 45 and HeatMaster 60 boilers. The thermostat acts as a high-limit or safety device, interrupting the control circuit when the sensed temperature exceeds the setpoint. The reset function allows rearming after the temperature drops. The bulb form can be immersion or clamp-on, and the contact configuration is normally closed or normally open, with electrical rating matching the original.

When selecting a replacement thermostat of this type, verify the switching temperature (setpoint), reset type (manual or automatic), capillary tube length, and bulb form (immersion or clamp-on). The electrical rating and contact configuration (normally closed or normally open) must match the original. Ensure the capillary length reaches the mounting point without sharp bends, and that the reset mechanism is accessible. For clamp-on bulbs, secure correctly and apply heat-conductive paste for accurate response.

Typical failures include drifting switching point, causing the boiler to modulate incorrectly or fail to cut off. A broken capillary tube or poor thermal contact between the bulb and pipe can also occur. Check for these issues if the boiler overheat protection is not functioning properly.