RV Leak Detection After Winter: Find Plumbing Leaks | Black Series

Apr 26, 2026

RV Leak Detection After Winter: Find Plumbing Leaks

The fastest way to find RV plumbing leaks after winter is to fill the fresh water system, turn the water pump on with every faucet closed, and listen. If the pump cycles on by itself every few seconds or minutes, water is escaping somewhere. Then work through the usual suspects with a flashlight and paper towels: the water pump, PEX fittings, low-point drains, the water heater bypass and drain plug, the toilet valve, faucets, the outdoor shower, and the city-water inlet check valve.

Freeze damage almost always shows up at de-winterizing, not during storage, because the system sits empty or full of antifreeze until you pressurize it again. Catching a leak in the driveway is far better than finding a soaked floor three days into a boondocking trip.

Why Freeze Damage Shows Up at De-Winterizing

Water expands as it freezes. Any water left in a low spot, a fitting, a valve body, or the pump head can crack plastic, split a fitting, or push a seal out of place. Over the winter, nothing leaks because there's no pressure on the lines. The moment you turn on the pump or connect city water, those hidden cracks start weeping.

Even a well-winterized trailer can have trouble. Antifreeze may not have reached every line, a low-point drain may have been left closed, or a check valve may have trapped a little water. Off-road trailers add vibration and flex to the mix, which can loosen fittings over a season of washboard and rocky trails. Our article on what breaks first after winter covers the most common failure points in more detail.

Pressure-Testing the Fresh Water System

The pump-cycling test

This is the single most useful test you can do. Flush out antifreeze first, fill the fresh tank, close every faucet and drain, and switch the water pump on. Let it build pressure and shut off. Then stay quiet and listen for five to ten minutes. A tight system should hold pressure and the pump should stay off. If it cycles on briefly on its own, you're losing pressure through a leak, a dripping faucet, or a leaking check valve. If the pump never shuts off at all, look for a large leak, an open faucet or drain, or an empty tank.

City-water test

Repeat the test on city water with a pressure regulator at the spigot. City water can expose leaks the pump doesn't, simply because the pressure is often higher. If you have an inexpensive pressure gauge with a hose fitting, you can watch for a pressure drop with the spigot turned off.

Where to Look for Leaks

Work methodically, starting at the water source and following the water. Your owner's manual shows where your trailer's components are; layouts vary between models.

Water pump

Check the pump head, inlet strainer, and both connections. A cracked pump housing or strainer bowl is one of the most common freeze failures. Look for drips or a damp spot directly under the pump.

PEX lines and fittings

PEX tubing itself tolerates freezing fairly well, but the crimp rings, elbows, and tees do not. Run a dry paper towel around each accessible fitting and look for any dampness. Our guide to finding a PEX fitting leak fast covers tracing technique.

Low-point drains

These are often under the trailer and easy to forget. Make sure they're closed and that the caps or valves aren't cracked.

Water heater bypass and drain plug

Confirm the bypass valves are back in the normal position, then check each valve body for cracks. Inspect the drain plug or anode rod threads for seepage after the tank fills.

Toilet valve

A cracked toilet water valve often leaks only when you flush, or slowly drips behind the base. Flush a few times, then check the floor and the back of the toilet.

Faucets and outdoor shower

Faucet cartridges and the hot and cold lines feeding them can crack if water was trapped. The outdoor shower is a frequent offender because it sits in an exterior compartment that gets colder than the cabin. Open each faucet briefly, close it, and look underneath.

City-water inlet check valve

If water comes out of the city inlet when the pump is running, or the fresh tank fills on its own while on city water, the check valve is likely damaged. See fixing a city water check valve for the repair.

Roof and Window Leaks vs. Plumbing Leaks

Not every wet spot after winter is plumbing. Snow load, ice, and UV can open up roof seams and window seals too. A few clues help you tell them apart:

Plumbing leaks appear when the system is pressurized, usually near fixtures, under sinks, or along floor-level runs, and they happen regardless of weather.
Roof and window leaks appear after rain or washing, often show staining on ceilings or upper walls, and stay dry when the pump is on and the sky is clear.

If you suspect water from above, check the sealant around vents, the AC, and windows. Our article on where trailers leak first on the roof is a good starting point.

Tools for Leak Detection

Bright flashlight or headlamp to see into cabinets, compartments, and under the trailer.
Paper towels to wipe fittings dry, then wrap and recheck. Even tiny seeps show up as a damp spot.
Moisture meter to check floors, walls, and cabinet bottoms for hidden water that has already soaked in.
Inspection mirror for the backs of fittings you can't see directly.
Water pressure regulator and gauge for city-water testing.

Step-by-Step Post-Winter Inspection

Close all low-point drains and the water heater drain plug, and return the bypass valves to normal.
Flush antifreeze from the lines and sanitize the system per your owner's manual.
Fill the fresh tank, turn on the pump, and bleed air from each faucet until water runs steadily.
Close all fixtures and listen for the pump cycling over five to ten minutes.
Start at the pump and follow the lines, wiping each fitting with a paper towel.
Check the water heater fittings, drain plug, and bypass valves.
Run each faucet, shower, and the toilet, then inspect underneath.
Check the outdoor shower and city-water inlet.
Connect city water through a regulator and repeat the pressure and visual checks.
Use a moisture meter on floors and cabinet bottoms near plumbing runs, then recheck everything after 24 hours.

Our RV checklists include a winterizing list you can reverse for spring.

DIY Fixes vs. Professional Repair

Many post-winter leaks are straightforward DIY jobs: tightening a loose fitting, replacing a cracked pump strainer, swapping a faucet cartridge, or replacing a damaged check valve. PEX repairs are doable if you have the right crimp or push-fit fittings and access to the line.

Call a pro when the leak is inside a wall or under a floor you can't open, when you find soft or delaminating flooring, when the water heater tank itself is cracked, or when the leak is near propane lines or 120-volt wiring. Propane appliances and internal 120-volt electrical work should always be handled by a licensed technician. If your trailer is under warranty, contact the dealer or manufacturer before opening panels.

Preventing Leaks Next Winter

Open every low-point drain and the water heater drain, and blow out lines with low-pressure air before adding antifreeze.
Bypass the water heater so you aren't filling the tank with antifreeze.
Run antifreeze to every faucet, the toilet, and the outdoor shower until it comes out pink at each one.
Drain the pump and strainer, or run antifreeze through them.
Leave faucets slightly open in storage, unless your owner's manual says otherwise.
Write down every valve you moved so de-winterizing goes in reverse without guesswork.

On an off-road trailer like a Black Series that sees heavy trail vibration, it's also worth checking fitting tightness at the start of each season, not just after winter.

Frequently Asked Questions

Why does my RV water pump turn on by itself?

The system is losing pressure. The cause is usually a leaking fitting, a dripping faucet, a cracked pump component, or a faulty check valve letting water flow back.

How long should I pressure-test after de-winterizing?

Listen for at least five to ten minutes with all fixtures closed, then recheck the next day. Slow seeps sometimes take hours to show.

Can PEX pipe burst from freezing?

PEX tubing is fairly freeze-tolerant, but fittings, valves, and pump components are much more likely to crack. Check fittings first.

How do I tell if water damage is from the roof or the plumbing?

Plumbing leaks happen when the system is pressurized, no matter the weather. Roof and window leaks show up after rain or washing and often stain upper walls or ceilings.

Is a moisture meter worth having?

Yes. It finds water that has soaked into floors or walls before it causes visible damage, which is when repairs are cheapest.

Should I fix a water heater leak myself?

Replacing a drain plug or bypass valve is often a simple DIY job. A cracked tank, or anything involving the propane or 120-volt side of the heater, should go to a licensed technician.

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