or the unit tripping the internal thermal overload protector

this 1/2" immersion well ensures your controls receive the accurate temperature data required for efficient boiler cycling and system protection

What does it mean if the status light isn't flashing

check system flow requirements before installing in heat pump liquid lines

McDonnell & Miller FS4-3S Switch 320720-756 or the unit tripping theThe McDonnell & Miller FS4 3S (Part Number 114641) is a rugged general purpose liquid flow switch specifically engineered for high demand hydronic and industrial applications. This 1" NPT flow switch features a high grade stainless steel body and hardened stainless steel bearings to minimize friction and prevent mechanical failure in the field. Designed as the direct replacement for FS4 3S E, it integrates a Single Pole Double Throw (SPDT) snap switch