RV Water Pump Not Working - Diagnosis and Fix
You flip the pump switch and nothing happens. Or it runs non-stop without building pressure. Or it cycles on and off every few seconds even with no faucets open.
Each symptom points to a different problem. Here’s how to diagnose and fix all of them.
Pump Won’t Turn On At All
Check the Fuse
The water pump has a dedicated fuse in the 12V panel. Pull it and inspect. Replace blown fuses with the exact same amperage — usually 10 or 15 amp.
Check the Switch
The pump switch on the wall sends 12V to the pump. If the switch is bad, no power reaches the pump. Test with a multimeter at the switch terminals. You should see battery voltage (12-13V) when the switch is on.
Check Battery Voltage
The pump needs at least 10.5V to run. A dead or weak battery won’t power it. Check voltage at the battery terminals with a multimeter.
Check the Pump Directly
If fuse and switch are good, test the pump by connecting it directly to 12V with jumper wires. If it runs, the wiring between the switch and pump has a break. If it doesn’t run, the pump motor is dead.
Pump Runs But No Water
Empty Tank
Sounds obvious. But the tank gauge in most RVs is inaccurate. Open the gravity fill cap and look inside.
Lost Prime
If the tank has water but the pump can’t pull it, the pump lost its prime. Air in the suction line prevents the pump from drawing water.
To re-prime:
- Open the faucet closest to the pump
- Turn the pump on
- Let it run 30-60 seconds
- Water should start flowing in spurts, then steadily
If it won’t prime, check the suction line from tank to pump for air leaks. Cracked hose fittings or loose clamps let air in.
Clogged Filter
Most RV water systems have an inline strainer between the tank and pump. Sediment, debris or antifreeze residue can clog it. Remove and clean or replace the screen.
Pump Cycles On and Off
This is the most common complaint. The pump builds pressure, shuts off, then kicks on again seconds later — even with all faucets closed.
Leak in the System
The pump pressurizes the lines to about 40 PSI, then the pressure switch shuts it off. If pressure drops (from a leak), it kicks on again.
Check every faucet, toilet valve, shower head and fitting for drips. Don’t forget the outdoor shower and ice maker line.
Worn Check Valve
The pump has an internal check valve that prevents backflow. When it wears, water bleeds back through the pump, dropping pressure. The pump then cycles to re-pressurize.
Some pumps have a replaceable check valve. Others require full pump replacement.
Pressure Switch Adjustment
Some pumps have an adjustable pressure switch. If it’s set too sensitive, the pump cycles at minor pressure fluctuations. Adjust it slightly less sensitive (consult your pump manual for the screw location).
Pump Replacement
When the pump motor is dead, the impeller is damaged or cycling can’t be fixed, replace the entire unit.
Popular replacement pumps:
- Shurflo 4008 (3.0 GPM, quiet)
- Shurflo 4048 (4.0 GPM, higher flow)
- Flojet Triplex 3526 (2.9 GPM, smooth flow)
How to Replace
- Turn off the pump switch
- Disconnect the battery (safety first)
- Close the fresh tank valve if equipped
- Disconnect inlet and outlet hoses (have towels ready)
- Disconnect wiring (note which wire goes where)
- Remove mounting screws
- Install new pump — match hose sizes and wiring
- Fill the tank and prime the new pump
- Check for leaks at all connections
Most pumps use standard 1/2” hose barb fittings. If yours is different, adapters are available at any RV parts store.
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