The controller measures the temperature of a roof mounted collector and the temperature of a water storage tank. When the tank temperature is low and the collector is hot, the controller will turn on the pump to recirculate water from the tank through the collector. Water passing through the collector will be heated from the sun.
If the water in the tank is already hot, then the pump will not run regardless of how sunny and lovely the day is.
Temperature Sensor Inputs
The controller requires either 2 or 3 temperature sensors, depending upon the type of tank.
Most installations will use 2 temperature sensors. One sensor will be placed in the water tank and be connected to the Tank Bottom input. The other sensor will be placed up at the collector and be connected to the Solar Collector input.
The 85°C/75°C link should be REMOVED for the 2 sensor system.
In the 2 sensor system, the pump will only operate if the collector is hot and the tank temperature is below 82°C. It will turn the pump off when the tank temperature reaches 85°C.
Other installations that have a lower temperature water tank use 3 temperature sensors. Two sensors are placed in the water tank, one near the bottom the other near the top. This is to ensure no part of the tank ever gets too hot. They are connected to the Tank Bottom and Tank Top inputs. The third sensor will be placed up at the collector and be connected to the Solar Collector input.
The 85°C/75°C link should be INSTALLED for the 3 sensor system. Do not remove the link as the tank may be damaged and is costly to replace.
In the 3 sensor system, the pump will only operate if the collector is hot and the tank temperature is below 71°C. It will turn the pump off when the tank temperature reaches 74°C. Only the bottom sensor is used to determine if the pump should turn on, but it will turn off when either sensors detects it's too hot.
The three sensor system also supports frost prevention. If the collector temperature falls below the defrost threshold, the pump will turn on to pump hot water from the tank through the collector coils to protect them from the effects of the water freezing in the tubing. Pumping will continue for at least 15 minutes, unless a sensor fault is detected.
The indicator LED may help diagnose faults. It indicates the following things:
LED Steady On
Normal. System is idle. Pump is off.
1 short flash
Normal. Pump is running.
2 short flashes
Fault. A temperature sensor is faulty.