Cooling Tower Overflow [updated] Jun 2026

If the operating level is set too high, the natural turbulence of the water or the "drain back" that occurs when pumps shut down will push the water level over the overflow weir.

Ignoring a steady trickle from an overflow pipe can result in surprisingly high expenses.

In modern facilities governed by Building Automation Systems (BAS), the problem is often digital rather than purely mechanical. These systems rely on level sensors—typically ultrasonic, capacitance, or conductive probes—to relay data to the control panel. If a sensor becomes fouled with biological growth (biofilm) or scale, it may report a "low level" reading when the basin is actually full. Consequently, the automation system commands the makeup valve to open, causing an overflow event. This highlights the critical need for regular sensor calibration and cleaning; a dirty sensor is not just inaccurate, it is financially wasteful.

You aren't just losing water; you are losing the expensive corrosion inhibitors, biocides, and scale dispersants added to that water. This leaves your internal piping vulnerable to rust and biofouling. cooling tower overflow

Would you like a troubleshooting checklist or guidance on adding a high-level alarm system?

Upgrade from mechanical floats to multi-point electronic sensors. These are more reliable and can be integrated into a Building Management System (BMS).

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If the building’s city water pressure is too high, it can force its way past valves that aren't rated for such force, leading to a slow, constant leak into the basin. The Real Cost of a Leaking System

To understand why a cooling tower overflows, one must first understand its standard operation. The tower relies on a basin, or sump, to hold a specific volume of water. As water evaporates during the cooling process, the level drops, triggering a makeup water valve to open and replenish the supply. Overflow occurs when the input of water exceeds the system's capacity to contain or evaporate it. The failure usually originates from one of three distinct sources: mechanical failure, control logic errors, or hydraulic imbalances.

Ensure there is enough space between the "fill" level and the "overflow" level to handle pump-stop surges. This highlights the critical need for regular sensor

To give you the best advice for your specific system, let me know:

Debris or a small pebble often gets stuck in the makeup valve, preventing a full seal.

If you find your tower is currently overflowing, follow these steps:

Modern towers often use electronic water level sensors or ultrasonic transmitters. Scale buildup or electrical failure can "blind" these sensors, causing the controller to keep the makeup solenoid valve open.