RV Water Pump Won't Stop Running? Find the Leak, the Air, or the Check Valve

Everything is closed. No faucet is open, nobody is in the shower, and every thirty or forty seconds the pump under the dinette wakes up, thumps for a second, and shuts off again. Or worse — it runs and runs and never shuts off at all, and the faucet only sputters.

Those are two different failures with two different search paths, and the mistake most owners make is replacing the pump for either one. A demand pump is a dumb device: it runs whenever the pressure it sees drops below its cut-in point, and it stops when pressure climbs back to cut-out. If it keeps running, either something is bleeding pressure off the system, or the pump can't build pressure in the first place. Your job is to find out which.

Sort the symptom first — it cuts the search in half

• Short-cycling. Pump kicks on for a half second every 20 seconds to a few minutes, with everything closed. The system is holding pressure, then losing it. Something is leaking — forward into the coach, or backward into the fresh tank.
• Runs constantly, weak or sputtering flow. The pump never reaches its cut-out pressure. That's almost always air on the suction side, a blocked strainer, or a worn pump head — not a leak.
• Runs constantly, strong flow, no shut-off. Pressure switch or a genuinely open outlet — a low-point drain, an outside shower wand left cracked open, or a city-water inlet check valve that's stuck.
• Cycles only when you use water, then settles. That's normal. A demand pump with no accumulator pulses under low flow; it's annoying, not broken.

The five-minute test that proves whether you have a leak

Don't chase puddles yet. Prove the system does or doesn't hold pressure.

1. Close every faucet inside and out, including the outside shower wand and the toilet sprayer. Confirm both low-point drain valves are fully shut and the city-water hose is disconnected.
2. Switch the pump on and let it pressurize until it shuts itself off.
3. Now switch the pump off at the panel and walk away for fifteen minutes.
4. Come back and open a faucet. A solid, pressurized spurt before the flow dies means the system held. A limp dribble means pressure bled away — you have a leak.

If it held pressure but the pump still short-cycles with the switch on, the pressure switch is cutting in too early and the pump is chasing itself. If it didn't hold, keep going.

The two leaks that leave no puddle catch almost everyone:

• The toilet water valve passing. Watch the bowl for ten minutes with the pump on. If the water level creeps up on its own, the flush valve is seeping and the pump is repressurizing behind it. A ball-seal or valve-cartridge rebuild kit is $25–$60.
• The pump's own check valve. The check valve lives in the pump head. When it fails, pressurized water pushes backward through the pump and into the fresh tank — so the pump cycles forever and you never find a drop anywhere. Tell-tale: your fresh tank level creeps up while the coach sits, or you hear water trickling into the tank right after the pump shuts off.

Then go looking for the ordinary ones: hose-barb clamps at the pump, PEX crimp rings behind the water heater, the shower valve body, the T&P relief valve on the water heater dripping outside, and the fittings inside every basement compartment. Run a dry paper towel around each joint — it finds a weep your fingers won't.

Runs and runs but never builds pressure: work the suction side

When flow is weak and the pump surges, the problem is upstream of the pump, and it's usually air.

Check, in this order:

• Water source. Fresh tank actually has water in it, and the winterizing valve isn't still set to draw antifreeze from the siphon hose. This is the most common "broken pump" in April.
• The inline strainer. The clear bowl on the pump inlet clogs with tank debris and biofilm. Shut the pump off, unscrew the bowl, rinse the screen, and seat the O-ring clean. A dry or nicked O-ring on that bowl lets the pump suck air and is a classic cause of surging.
• Every inlet clamp and fitting between tank and pump. The suction side can leak air without leaking a drop of water, because it's under vacuum. Snug the clamps; replace any cracked plastic barb.
• The pickup tube in the fresh tank. A cracked or unseated pickup lets the pump gulp air once the level drops below the crack — which is why the problem often only shows up on a half-empty tank.
• The pump head itself. Diaphragm pumps wear. A pump past five or six hard seasons that runs loud, moves little, and can't hit cut-out has earned replacement. Budget $120–$220 for the pump and $150–$350 for mobile labor.

If the flow is fine but the pulsing drives you crazy, an accumulator tank is the real fix — a small bladder tank pre-charged with air a few psi below the pump's cut-in. When the bladder loses its charge or waterlogs, it stops damping and the pump starts hammering again; check its Schrader valve with a tire gauge before you blame the pump.

One habit worth building regardless: switch the pump off whenever you leave the RV or go to bed. A fitting that lets go with the pump on will pump the entire fresh tank into your floor. That single failure is behind a large share of the soft floors and delaminated walls we see.

When to call a pro

Call someone the moment water is where you can't see it:

• Water showing up on the floor, in a basement bay, or as a soft spot — the visible spot is rarely where the leak is, and finding it means pressure testing and a moisture meter.
• A leak you cannot locate after a careful pass, with the pump still cycling.
• A suspected freeze split in the underbelly or behind a wall after a season that got away from you.
• Anything that requires opening the underbelly, the heated enclosure, or a wall panel to reach the plumbing.

Because a water pump is where it is — under a bed, behind an access panel, three feet from the tank — this is mobile work. A tech comes to your site with the strainer O-rings, clamps, and a pump on the truck, which is what mobile RV repair in Denver and the rest of our RV repair coverage map is built around. If the trail leads to the water heater instead — a weeping T&P valve or a bypass valve that never fully closed — that's RV water heater repair in Phoenix territory, and our annual water heater checklist covers what to inspect while you're in there.

FAQ

Why does my RV water pump run for a second every few minutes with nothing on? The system is losing pressure. In order of likelihood: a toilet water valve seeping into the bowl, a failed check valve in the pump head pushing water back into the fresh tank, or a fitting weeping somewhere downstream. Run the fifteen-minute hold test above before buying anything.

Do I actually need an accumulator tank? Not to fix a leak — but yes, if your complaint is pulsing and noise at low flow. It gives the pump a cushion of compressed air so it runs in longer, quieter stretches instead of hammering.

Is it bad to run the pump dry? Yes. Most modern demand pumps tolerate brief dry running, but sustained dry running cooks the diaphragm and the motor bearings. If the tank's empty, switch it off.

Can I leave the pump on while driving? You can, and plenty of people do — but road vibration is exactly when a clamp or fitting decides to give up, and the pump will happily empty the tank into the coach. Switch it off between stops.

Still cycling after you've worked the list, or you've found water where it shouldn't be? Call 833-FIXED-RV (1-833-349-3378). One call, answered live by a real person 24/7, and we connect you to a vetted, licensed, insured local RV tech who comes to you — with a $2,500 Workmanship Guarantee behind the repair. It's free for RV owners to use.