RV water pump runs but no water comes out
The pump cycles or runs continuously but taps deliver nothing or only sputters.
Applies to: 12V demand pumps in towable and motorised RVs, including Shurflo Revolution, Aquajet and Flojet units.
Quick answer
What usually causes it
Fresh tank actually empty or gauge wrong
Most commonRV tank senders are notoriously unreliable and commonly read a quarter full when the tank is dry. Confirm by weight, by the fill sound, or by adding a known quantity of water.
Valve set to the wrong source
Most commonWinterising bypass valves, tank-select valves and low-point drains left open all cause the pump to pull from somewhere other than the fresh tank. After any winterizing or de-winterizing, this is the first thing to check.
Clogged inlet strainer
CommonThe inline screen ahead of the pump traps sediment and biofilm. A partially blocked screen lets the pump run fast and loud while moving very little water.
Air leak on the suction side
CommonA loose fitting or a cracked barb between the tank and the pump lets the pump draw air. Because the line is under vacuum rather than pressure, nothing leaks out and the fault is easy to miss.
Collapsed or kinked intake hose
Less commonFlexible intake hose can suck flat under vacuum, especially if it has softened with age or is routed with a tight bend.
Failed pump check valve or worn diaphragm
Less commonA pump that has run dry repeatedly can lose its ability to self-prime. It will run at full speed and build no pressure.
Step-by-step diagnosis
Work in this order. Each step is cheaper or safer than the one after it, so stop as soon as the symptom clears.
Verify there is genuinely water in the fresh tank
Do not trust the panel gauge. Add five gallons of known water and see whether behavior changes, or listen at the fill port. Empty tanks are the single most common cause of this complaint.
Walk every valve in the fresh water system
Check the winterizing bypass at the water heater, any tank-select or city-water diverter valve, and the low-point drains. Set the system to draw from the fresh tank and confirm all drains are closed. If the RV was recently winterized or stored, expect to find the answer here.
Open one tap and let the pump push air out
Open the tap physically closest to the pump, on cold, and let it run. A pump that has lost prime often needs 30 to 60 seconds of open-tap running to purge air and pull water through. Sputtering that steadily improves means it is priming.
Clean the inlet strainer
Close the tank valve or accept a small spill, unscrew the clear strainer bowl ahead of the pump, and rinse the screen. Reassemble finger-tight plus a light turn. Overtightening cracks the plastic housing and creates the exact air leak you are trying to avoid.
Hunt for suction-side air leaks
With the pump running, inspect every fitting between the tank outlet and the pump inlet. Snug loose clamps, re-tape threaded fittings, and look for hairline cracks in barbed elbows. A short piece of clear hose spliced in makes air bubbles visible immediately.
Check the intake hose for collapse
Feel the hose while the pump runs. A hose that goes hard and flat under vacuum, or that has a tight bend behind a panel, is restricting flow. Replace with reinforced hose rated for suction use.
Prime the pump manually if it still will not pull
Disconnect the inlet, fill the pump head and the short inlet section with water from a bottle, reconnect, and run it with a tap open. Self-priming pumps that have run dry often need this once to recover.
Test pressure output to confirm the pump itself
If the intake path is proven good and the pump still builds no pressure, drop the inlet hose into a bucket of water. If it pumps happily from the bucket, the fault is in the tank plumbing. If it still will not pump, the pump's check valve or diaphragm has failed and the unit needs replacing.
Safety notes
- Switch the pump off at the panel before opening any fitting, or it will start the moment pressure drops.
- Never run a demand pump dry for extended periods. It destroys the diaphragm and the check valve.
- Use potable-rated hose and fittings on the fresh water side only.
When to call a professional
Plumbing behind sealed cabinetry, a fresh tank that leaks at the outlet fitting, or damage to a tank sender assembly are worth handing to a technician, mostly because access is destructive rather than because the repair is hard.
Frequently asked questions
Why does my RV water pump run constantly and never shut off?
A pump that never reaches cut-off pressure is either pulling air, feeding an open tap or a leak, or has a failed pressure switch. Check for a running toilet valve and an open low-point drain first, then look for suction-side air leaks.
Do I need the water pump on when connected to city water?
No. On city water the mains pressure feeds the system directly and the pump should be switched off. Leaving it on with city water connected can make it cycle intermittently and wear the pressure switch.
Why is my water sputtering after de-winterizing?
Air trapped in the lines. Open each tap in turn, farthest from the pump last, and let it run until the flow is steady. Do not forget the shower, the outside shower and the toilet valve.
Can a clogged strainer damage the pump?
Yes. Starving a diaphragm pump on the inlet side makes it run hot and fast with no cooling flow, which shortens the diaphragm's life considerably. Clean the strainer at least once a season.
Also described as
- rv water pump not pulling water
- camper water pump runs no pressure
- rv water pump lost prime
- rv faucet sputters air
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