Troubleshooting a Pump That Won't Prime

A pump that won't prime is one of the most frustrating problems in irrigation. The motor runs, you can hear it humming away, but nothing comes out. Before you panic, let's work through the most common causes.

What is Priming?

Priming means getting water into the pump housing so the impeller can do its job. Pumps don't pump air — they pump water. If there's air in the housing, the impeller just spins uselessly.

The Troubleshooting Checklist

1. Check the Suction Line for Air Leaks

This is the #1 cause. Any tiny air leak on the suction side (between the water source and the pump) will prevent priming.

• Check all fittings for cracks or loose connections
• Check the suction pipe for damage
• Check the foot valve (the check valve at the bottom of the suction line in the water source) — if it's stuck open, water drains back and air enters
• Check the thread sealant — use Teflon tape AND pipe dope on all threaded connections on the suction side

2. Check the Priming Pot

Most surface pumps have a priming pot or port on top.

• Remove the priming plug
• Fill the pump housing completely with water
• Replace the plug
• Try to start the pump immediately

3. Check the Foot Valve

Wade out to your water source (or pull up the suction line if possible) and check the foot valve:

• Is it clogged with debris?
• Is the screen intact?
• Does the flapper valve seal properly?
• Is it submerged deep enough? (At least 12 inches below the water surface)

4. Check Suction Lift

Surface pumps can only lift water about 25 feet vertically. If your pump is more than 25 feet above the water source, it physically cannot prime regardless of what you do.

• Measure the vertical distance from the water surface to the pump
• If it's over 20 feet, you're pushing the limits
• Over 25 feet? You need a submersible pump or need to relocate the surface pump closer to the water

5. Check the Impeller

If you've ruled out everything else:

• The impeller may be damaged or worn
• Debris might be jammed in the housing
• The pump may need to be opened and cleaned or serviced

Prevention

• Always install a quality foot valve with a screen
• Use check valves to keep water in the suction line when the pump is off
• Insulate suction lines if they're exposed to heat (warm water holds less air)
• Run the pump regularly — sitting idle for months can dry out seals and let air creep in