High or Low Limit & Circulator Strap-On Aquastat, 65-200°F range, 5-30°F Adj Differential. Strap-On Aquastat Controllers from Honeywell regulate the temperature of liquids in boilers, storage tanks, and more. These completely enclosed snap-acting switches operate on temperature rise to set point and are designed for circulator, low-limit, high-limit or unit heat control.