Quick answer: Start with what the pump does, not with the pump. If it runs or pulses while every tap is closed, look for a leak or air on the pressure side. If the motor runs but little or no water comes out, look at the inlet side: an empty tank, a clogged strainer, an air leak or a stuck valve. If it switches on and off quickly while a tap is open, look for a restriction at the tap or shower head. Water on the floor, a hot or melted wire, or a cracked pump housing means stop.
This guide covers the 12V pressure pump that feeds most RV faucets, and the parts around it: the inlet strainer, the pressure switch and the check valves. It does not cover city-water pressure regulators, water filtration or tank sanitizing. Makers differ and models differ, so your pump’s manual comes before this article.
Stop and call a technician
This comes first on purpose. Stop and get a qualified RV technician if any of these is true.
- Water keeps collecting under or around the pump or on the floor after you shut the pump off. A pump that runs with taps closed can mean a leak. Turn the pump off at its switch and see RV water damage signs and repair.
- A wire is hot, discolored, smells burnt or looks melted, or the fuse blows again right after you replace it. Water and electricity do not mix. Turn off the pump switch and leave it off.
- The pump housing is cracked. The manufacturer’s checklist (Pentair-SHURflo) lists cracks in the housing as something to check. A cracked housing is a replacement item, not a taping job.
- The system or pump may have frozen. SHURflo warns that freezing can cause “serious damage to the plumbing and the pump.” Do not force a frozen pump to run. Let everything thaw first.
- The problem leads to 120V equipment (a converter, charger or the water heater’s electric element). Your pump runs on 12V DC, the only wiring this article covers. We give no 120V steps. If tracing a wire leads there, stop.
- You have to open a pressurized line and are unsure how. The sources we read give no pressure-release procedure, so check your manual first.
If your checks take you near the water heater or another propane appliance, smell propane, or a detector alarms, stop and follow that appliance’s manual; see our RV water heater guide. Keep your propane and carbon monoxide detectors working and test them by the maker’s instructions.
Never use automotive antifreeze in a drinking-water system. SHURflo says such solutions “are highly toxic.” Winterizing is a different job; see how to winterize an RV water system.
Three symptoms, three different problems
A pressure pump has a simple job. It pulls water from the tank through a strainer, pushes it through check valves, and a pressure switch turns the motor on and off. SHURflo’s troubleshooting list sorts problems by what you observe. So do we.
| What you observe | Likely area | First check | Owner or technician |
|---|---|---|---|
| Runs or pulses with all taps closed | Pressure side: leak, air, valve, pressure switch | Look for leaks at taps, valves and the toilet; air in the water heater or pump head | Owner: visual checks. Technician: switch, internal valves, wiring |
| Motor runs, little or no water, sputtering | Inlet side: tank, strainer, air leak, stuck valve | Water in the tank? Strainer clean? Kinked hose? | Owner: tank, strainer, hose. Technician: stuck check valve, pump head work |
| Turns on and off quickly while a tap is open | Restriction on the outlet side | Faucet aerators and shower heads; filter on its own line | Owner: clean aerators. Technician if it persists |
| Dead, no hum | Power | Fuse or breaker, switch, connections, ground | Owner: fuse and switch. Technician: wiring faults |
The first three rows come from SHURflo’s list. The dead-pump row comes from its “pump won’t start / blows circuit” checks.
Before you open anything: power, voltage and the strainer
Do these first. They are cheap, and many symptoms come from them.
- Shut the pump off at its switch. If you must work near the pump or its wiring, pull the pump’s fuse or disconnect the battery as your manual directs.
- Check the basics. SHURflo lists the electrical connections, the fuse or breaker, the main switch and the ground connection. It also says driving vibration can loosen plumbing, strainers and pump hardware, and that many symptoms can be fixed by tightening loose components.
- Mind the voltage. SHURflo says to check that the charging system delivers correct voltage (plus or minus 10 percent) and a good ground, and to measure it while the pump is running, not at rest. Flojet’s datasheet for its R3426504A pump gives 12 VDC nominal with a range of 9 to 13.6 VDC and a 5 amp fuse. That is one example model. Yours may differ, so use your pump’s label and manual. Low voltage from a weak battery or a failing converter can look like a pump problem. When the converter is the suspect, our converter-versus-battery guide (planned) will cover it.
- Check the thermal protection. SHURflo notes that a hot motor may have tripped its internal thermal breaker, which resets once the motor cools. Flojet lists thermal motor protection on its example model. If it trips again and again, find out why. Do not just wait and retry.
- Check the inlet strainer. SHURflo lists a clogged strainer, kinked hose or restrictive valve as a restricted inlet, and notes that some systems have a strainer inside the tank. Flojet’s datasheet says a strainer is “required in all applications” to keep the check valves and pressure switch from clogging. If your pump has no strainer, ask a technician about adding one that suits your model.
Symptom 1: it runs or cycles when no tap is open
If the pump comes on by itself, or pulses every few minutes, pressure is dropping somewhere. SHURflo’s list for a pump that will not shut off, or runs with taps closed, names these causes:
- A leak on the outlet (pressure) side. SHURflo says to check the pressure-side plumbing for leaks and to inspect valves and the toilet. The toilet is named explicitly.
- Air trapped on the outlet side, such as in the water heater, or in the pump head. Our RV water heater guide covers the heater itself. We do not repeat the gas and electric steps here.
- A bad city-water or tank-fill valve. SHURflo lists this too.
- Debris holding the pump’s valves open, or swollen rubber.
- Loose drive-assembly or pump-head screws.
- The pressure switch. SHURflo says to check the pressure switch operation. Its separate “pump won’t start” list adds a test that bypasses the switch to see whether the pump runs. That involves live 12V wiring, so we treat it as technician work.
- Bypass pressure set higher than shut-off pressure. SHURflo mentions this check for its integrated-bypass pump. How to adjust it varies by model and we found no manual that gives a safe procedure, so we give no adjustment steps. If you suspect it, ask a technician and use your manual.
A quick way to separate a leak from a pump fault. Turn off the pump and look for drips at each tap, the toilet and the water heater. Look under sinks and around the pump for moisture. A pump that stops running after you correct a drip, or after a loose connection is tightened, points to a leak. A pump that still runs with no leak and no open tap points to the pump or its switch. This is our reading of the SHURflo list, not a maker’s test. Be careful with any pressurized part.
Symptom 2: it runs, but no water comes out, or it sputters
SHURflo’s list for a pump that does not prime, or sputters, with the motor running:
- Is there water in the tank? The list asks this, and also whether air has collected in the water heater.
- Is the inlet sucking air? A loose fitting on the inlet side is a vacuum leak. Check inlet connections and tubing.
- Is the strainer clogged? See the section above.
- Is the plumbing kinked or restricted? SHURflo includes clogged or restrictive winterizing valves. If you recently winterized or de-winterized, check that the valves are back in their normal positions. Our winterizing guide covers that process.
- Is a check valve stuck? SHURflo lists a stuck check valve and debris, swollen or dried-out valves in the pump head. Replacing these is a service-kit job. Flojet’s datasheet lists check-valve assemblies as service parts for its example model. Ask your pump’s maker for the kit that fits your model.
- Is the pump housing loose or cracked? Loose screws are fixable. A crack is not (see the stop list).
- Bad city-water or tank-fill valve. SHURflo lists this as another cause.
Dry running. It depends on the model. Flojet’s example datasheet says “Runs dry without damage.” We read no equivalent statement for other pumps, so do not assume yours can. Fill the tank or check the inlet before running it again.
Symptom 3: it switches on and off quickly while a tap is open
SHURflo’s rapid-cycling list is short:
- Look for restrictions in the plumbing, at faucets and at shower heads.
- Clean the faucet aerators and shower heads of debris or mineral build-up.
- Put any water filter or purifier on its own feed line. SHURflo says it “should be on a separate feed line.”
If one tap causes it, clean that tap’s aerator first, with the pump off. If every tap does it, check the strainer and hoses, then ask a technician.
Flojet’s datasheet says an accumulator tank (an accessory) smooths flow and reduces cycling, and that its example pump’s internal bypass also reduces cycling. Flojet also notes its accumulator is not for use with variable-speed pumps. An accumulator is an add-on to ask a technician about, not a cure for a failing pump.
What to leave alone
Some forums describe turning a bypass or pressure adjustment screw. We found no manufacturer procedure in the sources we read, so this article gives no screw positions or pressure settings. The 30 PSI cut-off we cite is Flojet’s figure for one example model, not a spec for yours. Pressure switch work, bypass changes and live-wire testing are technician jobs.
Repair or replace
We give no price ranges because we found no source we could verify. In general, a service kit (check valves, port clips or mounting feet are examples Flojet lists for its model) is a fix for a worn part. A cracked housing, a failed motor or repeated blown fuses usually point to a replacement. A technician can tell which applies. Check warranty terms first; see Is an RV extended warranty worth it?. SHURflo also states that freeze damage voids its warranty.
FAQ
Why does my RV water pump keep running when no one is using water?
SHURflo’s list names leaks on the pressure side, leaky valves or a toilet, air in the water heater or pump head, debris or swollen rubber in the pump valves, and a faulty pressure switch.
Is it safe to run the pump dry?
It depends on the model. Check yours. One example Flojet model is listed as run-dry capable. Others may not be.
Why does it switch on and off quickly with a tap open?
SHURflo points to restrictions at faucets and shower heads, mineral build-up in aerators, and a filter that is not on its own feed line.
Sources
Read 2026-10-20. Manuals and datasheets change; the manual for your own pump comes first. Claim-level detail is in the evidence file.
- Pentair-SHURflo, “RV Water Pump Maintenance and Troubleshooting,” reprinted by RVDA / RV Technician Today: rvda.org. This is a manufacturer article hosted by a third party. It names the SHURflo 2088 and 4008 pumps; we did not read their separate installation manuals.
- Flojet (Xylem), RV Water System Freshwater Delivery Pump R3426504A datasheet (Rev. A 04/2024). It is a datasheet for one newer model. It refers readers to the IOM for warnings, and we did not read that IOM.
General information, not a substitute for your manual or a qualified technician. RVFixWise Editorial drafts with AI assistance and checks claims against the sources above.
