RV water pump keeps running or cycling with no leak

Common symptoms

• The pump runs nonstop with every faucet closed.
• It kicks on for a second or two every few minutes, often at night, with nothing open.
• It stutters on and off fast while a faucet runs at a trickle.
• It keeps running for a long time after you close the tap.
• The fresh tank level creeps up while you are hooked to city water.

Quick checks before anything else

• Every faucet, the shower, the outside shower and any hose bib is fully closed.
• The fresh tank has water in it, checked by eye.
• The toilet bowl is not slowly filling with water.
• The low-point drain valves under the RV are closed.
• The tank fill or diverter valve is not left in fill mode.
• Nothing drips from the water heater relief valve or drain plug outside.

Why won’t the pump shut off?

A demand pump stops when the lines reach its shut-off pressure, and it starts again when the pressure drops. So a pump that keeps running or cycling is telling you one of two things. Water is escaping somewhere, or the pump cannot reach its shut-off pressure.

• Leak on the pressure side A drip at a faucet, fitting, low-point drain or water heater lets the pressure bleed away.
• Hidden leak with no puddle A toilet water valve or a tank fill valve sends water somewhere you cannot see.
• Leak back through the pump Scale or debris on the pump’s own valves lets water slip back toward the tank.
• Starved pump An empty tank or an air leak on the inlet means it never builds pressure.
• Low voltage A weak battery or thin wire leaves the pump too weak to reach shut-off.
• Switch or bypass problem A failed pressure switch, or a bypass turned up past the shut-off setting.

Step-by-step: find why the pump keeps running

When your RV water pump keeps cycling with no leak in sight, the leak is usually hidden. Work from the free checks to the pump itself. Turn the pump off and open a faucet to release pressure before you loosen anything.

1. Close everything and listen Close every tap, including the outside shower. Let the pump fill the lines and stop. Then wait and listen. Running nonstop points to a big leak, a starved pump or a switch fault. A short burst every few minutes points to a slow leak or leak back.
2. Rule out a starved pump Remco lists an empty tank and an air leak on the inlet side as causes of a pump that keeps running. If the faucets spit air, or the pump sounds rough, fix the supply first. Our guide to an RV water pump that runs but gives no water walks through the tank, strainer and inlet.
3. Check the toilet Shurflo names leaky valves or a toilet as a cause of a pump that won’t shut off. A worn toilet water valve lets water trickle into the bowl, and from there it drains into the black tank, so you never see a puddle. Dometic says that on 310, 311, 320 and 321 toilets a trickle for up to 20 minutes after a flush is normal, but past 30 minutes the water valve needs replacing. Our RV toilet leaking guide covers the valve and the drips behind the toilet.
4. Look for leaks on the pressure side Shurflo says to check the output side plumbing for leaks first. Use a flashlight under every sink, behind the shower panel, around the water heater and at the pump outlet. Outside, check the low-point drains and the water heater drain plug. A dripping relief valve on the water heater is easy to miss. See why an RV water heater relief valve leaks.

   

5. Check the tank fill valve Remco lists a fill valve bypassing to the tank as a cause of a pump that cycles with no water demand, and its fix is to replace the fill valve. Water leaking past it goes right back into the fresh tank, so it leaves no trace. Also make sure any diverter valve used to fill the tank is closed or turned back.
6. Flush and sanitize the pump valves Shurflo says lack of sanitizing causes scale on the diaphragm and valves, which leads to leak back: occasional cycling with no faucets open, or the tank filling while you are on city water. Shurflo also asks whether debris is holding the valves open or the rubber is swollen. Remco’s flush is to open all hot and cold faucets fully and let the water run a few minutes. If it still cycles after a full sanitize, replace the valve assembly or pump head for your model.
7. Measure voltage at the pump while it runs Remco lists low voltage as a cause and says to change the battery or check the wire gauge. Shurflo wants the pump within 10% of its rated voltage while running. Read the voltage at the pump wires with the pump off, then with a faucet open. Remco says a drop of more than 1 volt means the wire is too light.
8. Tighten the pump head screws Shurflo lists a loose drive assembly or loose pump head screws as a cause. Road vibration can work them loose. Snug them evenly. Do not overtighten plastic parts.
9. Look at the pressure switch and bypass If someone has turned the screws on a Shurflo, suspect them. Shurflo warns that if the bypass reaches full flow before the switch shuts off, the pump will not shut off, and that full bypass should be at least 10 psi above shut-off. It says only a technician with proper gauges should adjust the bypass. Remco says never to adjust its switch without asking the factory. A switch that fails can also leak or stay closed, and it is sold as a separate part.
10. Fix fast cycling at low flow If the pump stutters only while a tap runs slowly, Shurflo points to restrictive plumbing, flow restrictors in faucets and shower heads, a water filter on the main line rather than its own feed line, and a shut-off pressure set too low. Remco adds pulsations, fixed with a length of flexible hose called a pulsation dampener, and a clogged inline filter.

Shurflo, Remco and Flojet: do you need an accumulator?

An accumulator is a small tank with an air cushion that stores some pressure, so a slow flow or a tiny leak doesn’t kick the pump on every few seconds. Whether it helps depends on the pump.

Shurflo 4008. Shurflo says a bypass pump needs no accumulator. Its bypass starts opening at about 40 psi and gives smooth flow down to a trickle with virtually no cycling. If a 4008 cycles, look for a leak or a setting problem before adding parts.

Remco Aquajet. A variable-speed pump with an electronic controller and a combined pressure switch and bypass. Remco lists a faulty speed controller as one cause of a pump that won’t stop, and the fix is a call to the factory. For rapid cycling while water is flowing, Remco’s fix is its pulsation dampener hose.

Flojet R3426504A. It has an internal bypass and shuts off at 30 psi. Flojet sells a 1 liter accumulator to smooth out flow and reduce cycling, and says not to use it with a variable-speed pump.

An accumulator smooths cycling. It does not fix a leak, so a pump that loses pressure overnight still needs the steps above. For specs side by side, see our RV water pump problems guide.

When to call an RV tech

• The leak is inside a wall, under the floor or under the tank.
• A floor near the water lines feels soft or looks stained.
• The bypass or pressure switch needs adjusting. That takes a pressure gauge and, per Shurflo, a technician.
• A Remco pump still runs nonstop after the supply, leak and voltage checks, which Remco sends to the factory.
• Low voltage traces back to wiring or the converter, which our RV electrical guide covers.

Common questions