Symptoms of Water Pump Running Backwards – Solve It now!

If your water pump is running inefficiently or delivering a low flow of water, it is most likely operating backward. But how can you be sure? Are there any symptoms of water pump running backward?

The reduction in water flow and glycol pressure is an obvious sign of the incorrect rotational direction of a water pump. In addition, you can also verify it by checking the shaft of the motor.

Read on to understand the potential consequences of the water pump running backward, along with simple yet effective solutions.

Symptoms of Water Pump Running Backwards

reverse water pump

The water pump can run backward due to the silly mistake of the mechanic during repairing the machine. This error won’t hurt the machine immediately but will affect its performance and show some obvious signs.

The Shaft Will Turn the Wrong Way

A water pump mostly runs backward due to incorrect operation when using three-phase power in various applications. The mistake can happen when installing an electrical motor, a new pump, or adding a VFD. In addition, a mistake may also be made while replacing the motor or starter.

The most common symptom of a water pump running backward is that it will turn the wrong way. However, it can be checked quickly before causing anything wrong. Before connecting the motor to the pump, perform a bump test to ensure that the shaft is turning properly. A bump test means inspecting the rotation of the shaft. We’ll discuss it later.

Low Glycol Pressure

The low glycol pressure on the glycol pressure gauge is a symptom of the backward pump. Typically, the rotation is indicated on the pump head, where there is an arrow that goes counter-clockwise. And your water pump should run in this direction.

However, you can verify it by disassembling the motor, and it’s highly recommended that the process be handled by a certified electrician. He’ll turn the motor around, check the backside, and take the cap out. Then you can see there is a shaft in the center that spins clockwise after running the motor.

What Happens If a Water Pump is running backward?

water pump rotation direction

Typically, water pumps are directional, and they should start in the correct direction. However, they’ll hardly work if they spin backward. Your water pump will have an effect at some point, and the most common errors of running a water pump backward are:

The Engine will get Overheat

The most common consequence of running a water pump backward is that it will force the cold coolant out of the radiator through the thermostat and close it up. Hence, coolant will no longer enter the hot engine, and it’ll become overheated eventually. Even the blade can stall and splash water around the inside of the water pump.

Related Article: Coolant Reservoir Does Not Drain Back Into Radiator

Produce Less Water

The pump will deliver less water at a lower strain if it runs backward. However, it’ll consume less energy. The impeller can also thread into the shaft and unscrew if the water pump keeps running backward.

The Curvature of the Impeller’s Vanes

The effect of the water pump running backward also depends on the curvature of the impeller’s vanes. There are three types of vanes available: straight vane, forward vane, and backward vane.

If your water pump has a straight vane and it runs backward, it’s possible you won’t get any different performance in the flow or head. But if your pump has a forward vane, you’ll get a completely different result if it runs backward. Since its impeller will perform as a backward vane, it’ll change the pump’s characteristics completely.

What if Centrifugal Pump Run Backward?

Reverse rotation is a common mistake when operating a pump. Though backward-rotating impellers won’t refuse to work, they can reduce their performance and damage the internal parts.

If your centrifugal pumps motor runs backward, the flow can drop by up to 70%, causing the flow to be hampered. The pump will continue to function normally despite this. It can also jam the impeller and make it unthread.

Due to the pump’s acorn nut rotating backward, it can spin off quickly and damage the seals or bearings of the pump. If the mechanical seal breaches due to damage to the pump, keep it running; stopping it can cause injury. Even if you leave it unsolved, it can completely damage your centrifugal pump.

It’ll also affect the performance curve. In general, the vanes of the water pump come with specific impeller designs and angles to get crucial hydraulic properties that are potent on the performance curve of the pump. If the pump runs backward, it won’t deliver the same curve. As a result, it’ll hamper the flow, efficiency, pressure, and power consumption of the pump.

How to Reverse the Centrifugal Pump?

The impeller’s shape and the pump’s body design determine the direction of the liquid flows. If the pump’s impeller runs in reverse, the liquid will still discharge. The reason is that the centrifugal force will move the fluid in the right direction. Since the flow won’t reverse, detecting the reserve ratio of a centrifugal pump is a bit difficult.

This abnormal operation can have worse results if it happens after replacing the parts or installing the new pump system.

To avoid this error, check the rotational direction of the impeller before starting the pump. If your water pump is uncoupled, you can check it by applying a simple test called the bump test.

Your water pump will show the right rotational direction on the pump, casing, motor, or bearing frame.

Before utilizing the test, determine the right rotational direction by checking the rotation sticker. Then attach three wires to the motor, pump the power, and inspect if the shaft spins clockwise. If the shaft spins counter-clockwise, it means you have to customize something. In this case, change two of the three wires and try the test.

Though it may appear simple in theory, handling electrical wires can be extremely dangerous. It can injure you severely and damage the pump. So unless you have skills in electrical work, hire an expert electrician.

Also Read: 6.7 Cummins Water Pump Replacement

What if a Hydraulic Pump Runs Backward?

hydraulic pump rotation

If a hydraulic pump runs backward, it’ll damage the system that’s delivering power. Even reverse fluid flow through a system can cause damage to its components, like valves, pumps, and pipelines. However, many operators willingly run a hydraulic pump in reverse to create a little pressure to force air or fluid out of the system.

Backward rotation of hydraulic pumps can also cause cavitation or tiny bubbles that can damage the pumps severely. In addition, its fluid pressure can overheat the pump and end up causing it to explode.

Related Valve: How To Tell If Valves Are Bent After Timing Belt Broke?

How to Reverse a Hydraulic Pump

When it comes to checking a hydraulic pump, you should hire a mechanic to determine if it is pumping in reverse or not. Otherwise, if you have the skill, check the pump’s rotational direction based on the maker’s manual. The common procedure is to disconnect the power source of the pump and remove its hose and cap from the discharge port.

Then switch the tubing from the discharge port to other pressure sources, like the compressor or gasoline tank. You can also try connecting the tubing to the pump’s inlet port. Then re-attach the power supply and inspect if it’s working properly.


1. Can backflow damage a pump?

If the piping system gets a major elevation change, it can cause the pump to spin backward. If it remains unchanged, the pump or the pump drive can get damaged.

2. How to determine if the pump is rotating clockwise or counterclockwise?

If you inspect the pump from the shaft side and notice it’s rotating or spinning in the same direction as the clock, it means the pump is rotating clockwise.

3. Do pumps have a certain direction of rotation?

Centrifugal pumps can rotate both clockwise and counterclockwise. And you can determine its rotational direction facing the shaft.

Final Words

Obviously, running backward has adverse effects to a water pump which you shouldn’t take lightly. And tracking the symptoms of a water pump running backward can help you figure out the source of the problem. In most cases, a bump test is the simplest solution to restore the water pump to its proper condition and get the desired performance. Finally, don’t overlook this mistake for too long to avoid injury or severe pump damage.