Water pump getting hot and cutting out? Usually the thermal switch inside the pump has cut it off. The common causes of pump overheating, and how it differs from the controller's E8 fault.
A pump motor warms up a little while it runs, and that is normal. But if the pump body gets so hot you cannot keep your hand on it, or the pump stops mid-run and starts again after a while, something is wrong.
What "gets hot and cuts out" means
Most pumps have a thermal switch inside. When the motor gets too hot, this switch cuts the current, and it reconnects once the motor has cooled. In a building with a HYDROSET controller, at that moment the unit sees no current from the pump and shows fault E2.
The thermal switch has saved the pump, but the cause of the overheating is still there. Let the pump cool and find the cause.
Cause 1: dry running
The water passing through the pump is also what cools it. With no water, the temperature of the impeller and the seal rises within minutes. A cut in the supply, an emptied tank, a closed inlet valve and air in the pump all lead here. The HYDROSET controller detects this condition with E3 or E4 and stops the pump. Details in Dry running: causes and prevention.
Cause 2: running with no water flow
If the pump is on but no water leaves the outlet, for example because the outlet valve is closed, or because the pump cannot reach the F1 pressure and runs non-stop, the water inside the pump is churned constantly and heats up.
Cause 3: starting and stopping too often
Every start draws a large inrush current. If the pump starts and stops dozens of times an hour, the motor has no chance to cool. Why does the water pump keep starting and stopping?
Cause 4: current above the nameplate
A pump that draws more than its nameplate current runs hotter. A stiff shaft, a worn bearing or a weak capacitor pushes the current up. HYDROSET shows the pump's actual current on the display; if it goes above F3, the unit stops the pump and shows fault E1.
Cause 5: a hot, unventilated pump room
A closed pump room, one in the sun or one next to a heat source makes it hard for the motor to cool. Ventilate the pump room and keep the space around the pump clear.
Pump overheating versus fault E8
Fault E8 is about the temperature inside the controller itself, not the pump. The unit's permitted operating temperature is −15 to 55 °C. If E8 appears, wait a few minutes for the unit to cool; this fault clears by itself once the unit has cooled. Improve the ventilation where it is installed and keep the unit out of direct sunlight.
The order to check
| Symptom | Check this first |
|---|---|
| Got hot after the water was cut | Dry running, air in the pump |
| The pump never stops | F1, leaks, the bypass valve |
| The pump keeps starting and stopping | Gap between F1 and F2, vessel air pressure |
| Displayed current above the nameplate | Capacitor, shaft, bearing |
| E2 after a period of running | The pump's thermal switch |
| E8 on the display | Ventilation where the controller is installed |
