Why does my pump run but no water comes out?
Nine times out of ten it's lost prime — air in the pump or the inlet line. The pump spins but can't grab water. This happens after the fresh tank runs dry, after winterizing, or after any plumbing work. Refill the fresh water tank, open a faucet, and let the pump push the air out (more on priming below).
If the tank has water and the pump still won't pull, check the inlet strainer for debris and the inlet line for a leak or kink that's letting it suck air instead of water.
Why won't the pump shut off (or it pulses)?
A pump that short-cycles or pulses at the faucet is usually fine — that's the pressure switch reacting to low flow, and an accumulator tank smooths it out. A pump that runs constantly and never builds pressure, though, points to air in the system, a leak somewhere in the lines, or a worn pump that can't reach cutoff pressure.
How to replace an RV water pump
- Turn off the pump switch and the 12V power, and drain the lines by opening a low faucet.
- Disconnect the inlet and outlet lines (many use quick-connect fittings; some are threaded) and unscrew the pump from its mount.
- Mount the new pump on rubber feet or a soft pad to cut noise, and install an inlet strainer if it didn't come with one.
- Use short lengths of flexible hose at the inlet and outlet to reduce vibration and rattling, and confirm the arrows point in the direction of flow.
- Reconnect 12V (matching polarity), turn it on, and prime the system.
How to prime the water pump
Make sure there's water in the fresh water tank — a pump can't prime from an empty tank. Open a faucet, both hot and cold, and switch the pump on. It'll sputter and spit air at first; keep the faucet open until water runs in a steady stream with no sputtering, then move to the next faucet and repeat. Once every faucet runs steady, the system is primed and the pump should cut off when you close them.
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Frequently asked questions
Why does my RV water pump run but no water comes out?
It's almost always lost prime — air in the pump or inlet line, common after the tank runs dry or after winterizing. Refill the fresh water tank, open a faucet, and let the pump push the air out. Also check the inlet strainer and line for debris or a leak.
How do I prime my RV water pump?
Put water in the fresh water tank, open a faucet (hot and cold), and turn the pump on. Let it spit air until water runs in a steady stream, then repeat at each faucet. Once all faucets run steady, the pump is primed and will shut off when you close them.
Why won't my RV water pump shut off?
A pump that runs constantly without building pressure usually has air in the lines, a leak somewhere in the plumbing, or a worn pump that can't reach cutoff pressure. Brief pulsing at low flow is normal and an accumulator tank smooths it.