RV water pump runs but no water comes out

Common symptoms

• The pump hums or buzzes nonstop, but nothing comes out of the faucet.
• Water spits and sputters out of the tap with bursts of air.
• You get a short splash, then the flow dies while the pump keeps running.
• It stopped pumping right after you de-winterized the RV.

Quick checks before anything else

• Look at the fresh tank itself, not the panel gauge, and confirm there is water in it.
• The winterizing valve at the pump is turned to draw from the tank, not from an antifreeze hose.
• Any tank fill or diverter valve is set back to normal, not to fill.
• The clear strainer bowl on the pump inlet is clean and screwed on snug.
• One faucet is open while the pump runs, so trapped air has somewhere to go.
• If you just de-winterized, the hoses are connected to both pump ports.

What causes a pump to run with no water?

A diaphragm pump moves water by pulling it in on one stroke and pushing it out on the next. If it cannot pull water in, it just spins. So almost every cause sits on the suction side, between the tank and the pump.

• Empty tank or a valve set wrong The pump has nothing to pull, or it is pulling from the antifreeze port.
• Clogged strainer The flow is weak at first, then sputters, then stops.
• Air leak on the inlet side A loose clamp, fitting or strainer bowl lets the pump suck air instead of water.
• Air trapped in the lines or water heater Faucets spit and cough, and the hot side is worst.
• Debris in the pump valves or dry, stuck valves Common after storage or a sanitizing flush.
• Low voltage or a damaged pump A slow, weak pump, or a cracked housing or torn diaphragm after a freeze.

Step-by-step: get water flowing again

When your RV water pump runs but no water comes out, work from the tank toward the faucet. The early steps are free. Turn the pump off and open a faucet to release pressure before you loosen any fitting.

1. Check the tank with your eyes RV tank gauges often read wrong, so look at the tank or add a few gallons and listen. If the RV is parked nose up or tilted, water can sit away from the tank outlet, so the pump pulls air even with water in the tank. Level the RV and try again.
2. Set the valves back to normal Find the winterizing valve near the pump. It is usually a small lever or a three-way valve with a short hose. Turn it so the pump draws from the tank. Remco also lists a tank fill (diverter) valve left in fill mode as a cause of a pump that keeps running. Close or turn any valve used to fill the tank.
3. Clean the inlet strainer Unscrew the clear bowl on the pump inlet and rinse the screen under a tap. Shurflo says a strainer is required and names a clogged one as the first cause of a pump that will not prime. Remco says the screen must be cleaned on a regular basis or it will restrict water to the pump.

   

4. Do a gravity flow test If your tank sits higher than the pump, pull the inlet hose off at the strainer with the pump off and hold it over a bucket. Water should run out freely. Remco says water should flow from the tank at 2 gallons per minute (gpm) or more. A trickle means a kink, a blocked tank outlet or a closed valve before the pump. A strong flow means the problem is the pump or an air leak at its connections.
5. Bleed out the air Open the cold faucet closest to the pump, switch the pump on, and let it run until the flow is steady with no spitting. Then do each faucet, hot side too. Shurflo names air collected in the water heater as a cause, and a drained RV water heater has to fill before any hot tap flows. When Remco installs a new pump, it runs it 10 to 15 seconds to clear the air inside.

   

6. Hunt for air leaks on the inlet side Shurflo asks whether the inlet tubing is sucking in air at plumbing connections, which it calls a vacuum leak. This kind of leak lets air in rather than water out, so you rarely see a drip. Tighten hose clamps, check the strainer bowl and look for cracked barbs. On Remco and Flojet pumps with push-in ports, make sure each retainer clip is fully pushed down and the O-ring is in place.
7. Check the outlet side for blocks Shurflo lists severely restricted or kinked plumbing and restrictive valves on both the inlet and the outlet. Look for a pinched hose behind the pump and a clogged whole-house filter cartridge. Bypass any filter while you test.
8. Measure voltage at the pump while it runs Shurflo says to check for proper voltage with the pump operating, within 10% of the rating, and that lower voltage means lower flow. Remco’s test: read the voltage at the pump wires with the pump off, then again with a faucet open and the pump running. If it drops more than 1 volt, the wiring is too light. Remco’s Aquajet also shuts itself off below 11.5 volts.
9. Flush debris out of the pump valves Tiny bits of grit can hold the one-way valves inside the pump open, so it moves no water. Remco’s fix is to turn on all the hot and cold faucets all the way and let the water run for a few minutes. Shurflo adds that valves can also be swollen or dry after long storage, and that sealer or Teflon tape on the fittings can get into the pump and stop it from priming.
10. Look for freeze damage or a worn pump head Shurflo lists a cracked pump housing and loose drive assembly screws as causes. Look for cracks in the plastic head and water in the motor end, which Shurflo says points to a punctured diaphragm. If you find damage, replace the pump head with the kit for your model, or the whole pump.

Shurflo vs Remco vs Flojet: what differs

The checks above work for any 12V diaphragm pump. A few details differ by brand, so read the label on your pump before you order parts. Our RV water pump guide lists the full specs side by side.

Shurflo 4008. A bypass pump that shuts off at 55 psi (pounds per square inch). Shurflo wants it within 6 feet of the tank, with 1/2 inch inside diameter plumbing and flexible hose on both ports. Smaller plumbing, it says, causes cavitation (bubbles that form when the pump pulls harder than water can follow), low flow and noise.

Remco Aquajet. A variable-speed pump that Remco rates to prime up to 14 feet. It has a low-voltage cutoff at 11.5 volts, so a weak battery can stop it cold. Its ports are push-in fittings held by a retainer slide with an O-ring seal. Remco says not to adjust its pressure switch without asking the factory, and to call the factory about a perforated diaphragm.

Flojet R3426504A. A smaller pump that primes up to 8 feet and shuts off at 30 psi. It uses quick-connect ports with clips. Flojet says a strainer is required in all installs to keep the check valves and pressure switch from clogging.

If the pump runs fine but never stops once water flows, that is a different fault. Our guide to an RV water pump that keeps running covers it.

When to call an RV tech

• The lines or water heater froze and you see cracks or wet spots you cannot reach.
• The tank outlet itself is blocked inside the tank.
• The pump wiring drops more than 1 volt and needs a heavier wire or a relay, which Remco recommends a qualified tech install if you are unsure.
• The pump keeps blowing its fuse. That points to wiring, which our RV electrical guide covers.
• Water is leaking from the pump head as well, which we cover in RV water pump leaking.

Common questions