Prevent water damage: Turn the pump off whenever the RV is unattended. Stop immediately if water appears under cabinets, near electrical equipment or below the floor. Do not raise pressure settings to hide a leak.

The SHURflo Revolution 4008 is designed to slow as faucets close and stop when outlet pressure reaches its shutoff point. If it keeps humming with every fixture closed, the pump may be moving water through a leak, compressing trapped air, recirculating through its internal bypass or struggling with a valve or voltage problem.

Listen before touching anything. A smooth steady run suggests it cannot reach pressure. A run that changes pitch or nearly stops can point toward a small leak, air pocket or pressure-switch/bypass interaction.

Prove that every water path is closed

Close hot and cold faucets, the shower, outside shower, toilet valve, low-point drains and any appliance water valve. Make sure an outside shower is not left slightly open behind its service door. Check the city-water inlet for dripping and confirm the tank-fill or winterizing valve is in its normal camping position.

Dry the floor around the toilet, water heater, pump, filter canister and accessible fittings. Put a paper towel under suspect connections. A leak too small to form a puddle can still keep the pump below shutoff pressure.

Separate a plumbing leak from a pump problem

If the RV has an accessible shutoff valve immediately after the pump, close it briefly with the pump running. If the 4008 stops, pressure is escaping somewhere downstream. If it still runs, the issue is near the pump: inlet air, debris in the pump valves, internal leakback, bypass adjustment or the pressure switch.

Do not deadhead the pump against a closed valve longer than needed to observe whether it shuts off.

Purge trapped air, especially after service

SHURflo lists trapped air in the outlet line or water heater as a reason the pump may not shut off. Fill the fresh tank, confirm the water-heater bypass is in the correct position, then open one cold faucet until flow is solid. Repeat on the hot side and at the farthest fixtures.

If the system was just dewinterized, check that the water-heater tank is actually filling and that an empty filter housing is not holding air. A sputtering faucet is useful evidence.

Inspect the inlet side for air leaks

A loose strainer bowl, cracked housing, damaged O-ring, kinked suction hose or low tank level can let the pump pull air instead of a solid water column. Suction-side air leaks may not drip water outward. Clean the strainer, wet and seat its O-ring, and hand-tighten the bowl without distorting it.

If the pump never reaches a steady stream at a faucet, solve the prime or inlet restriction before adjusting pressure.

Check 12-volt voltage at the pump

The 4008 manual calls for voltage within 10 percent of rating. A weak battery, corroded ground, undersized wiring or failing switch can slow the motor enough that the pump never reaches shutoff pressure. Measure across the pump leads while it is running; a normal battery reading elsewhere does not prove voltage at the motor.

Know what the bypass adjustment can and cannot fix

The internal bypass is intended to reduce rapid cycling at low flow. SHURflo warns that if the bypass is set higher than the pressure-switch shutoff, the pump may never stop. That is most likely after someone has already adjusted the screws.

Mark the original position and use the exact 4008 manual before any adjustment. Do not simply tighten both settings. Wrong adjustment can increase system pressure, hide a restriction and shorten pump life.

When the pump head needs service

Debris or swollen internal valves can prevent the head from sealing. Loose pump-head or drive screws and a faulty pressure switch are also listed causes. If the RV plumbing holds pressure, the inlet is airtight and loaded voltage is correct, inspect or service the pump head using the correct model kit.

Replace a cracked housing or heat-damaged connector rather than trying to seal it with household adhesive.

Related RV Solver pages

Frequently asked questions

Why does my SHURflo 4008 run with every faucet off?

The pump may be feeding a small plumbing leak, pulling air, holding trapped air, leaking back through dirty valves, receiving low voltage or recirculating because the bypass is set incorrectly.

Can I adjust the SHURflo pressure switch to make it stop?

Only after leaks, air, restrictions and voltage are ruled out. Use the exact 4008 instructions and preserve the original setting; random adjustment can make the problem worse.

Can a toilet valve keep an RV water pump running?

Yes. A toilet water valve that does not fully close can pass enough water to prevent the pump from reaching shutoff pressure.

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Sources and review notes

Reviewed against manufacturer material on July 12, 2026. Match every fault definition, procedure, limit and replacement part to the exact model, specification and serial range installed in the RV.