ST-21 Central Heating Pump Controllers with LED Display

ST-21 controller with LED display is intended to control the central heating water circulation pump. The controller's task is to switch the pump on when the temperature reaches the set value and to switch it off when the boiler cools down below the set hysteresis value. Such a functioning mode prevents unnecessary operation of the pump, which allows to save electric energy and prolongs life of the pump as well as improves its reliability. ST-21 controller may also serve as a thermostat switching the pump off after reaching the set temperature. The controller also has an anti-stop function which prevents too long period of the circulating pump's operation standstill after the season (the pump is switched on approx. every 10 days for 1 minute). An additional protection is the anti-freeze function which prevents water freezing in the system (when the temperature drops below 6 °C, the pump is switched on permanently).