12v pumps

12V Soft Wash Pump Won't Prime? Try This First

Oct 31, 2026 Tim Cray 5 min read

Key takeaways

Prime it before you tear anything apart. Pull the outlet hose off the pump, run it 5 to 15 seconds until liquid pushes out, shut it off, and reconnect the hose all the way.
Check the simple stuff first. An empty tank or a pickup filter sitting above the liquid will make any 12V pump pull air.
Give the air 2 to 3 minutes to clear. If it never clears, you have a leak on the suction side, often a fitting on the mixer.
Keep debris out of the pump. Drilling a tank leaves plastic chips behind, so vacuum it out and run a slotted PVC pickup filter.
Pumps don't last forever. If priming, tight fittings and a clean tank don't fix it, the pump may be at the end of its life.

In this guide

FloJet 6 GPM 12V soft wash pump with blue quick-connect port clips

A 12V soft wash pump that hums along but won't move any liquid, or that spits air out the end of the hose, is one of the most common problems we hear about. It came up again recently in a Facebook post: a guy couldn't get his pump to prime no matter what he tried. Before you start pulling fittings apart or ordering a new pump, try the simplest fix first. It doesn't work every time, but it works often enough that it should always be step one.

Why 12V pumps don't prime

Most people hook up a 12V pump and never prime it. Sometimes it primes up on its own and runs fine. Sometimes it doesn't, and sometimes a pump that's been running fine loses prime. It's common after you reinstall mixer parts or hoses, or after a tank runs dry. When the pump head is full of air instead of liquid, it can run without ever pulling solution up out of your tanks and through the mixer.

Check the simple things first

Before you prime, make sure the pump actually has something to pull:

Every tank has liquid in it. If one of your tanks is empty, the system will pull air.
Every pickup filter is fully under the liquid. A filter sitting above the bleach, water, or soap pulls air the same way an empty tank does. It's not worth breaking down your whole system over a filter that's floating.

How to prime a 12V soft wash pump

In the video we're showing this on one of our Ultimate Mini skids with a FloJet 6 GPM pump, which is the 12V pump we like best. The pump's inlet is the suction side. On this setup it pulls out of the mixer. The outlet is the side that pushes solution out to your hose reel.

Disconnect the outlet hose. Pull the fitting off the outlet side of the pump. On the FloJet in the video it's a push-in quick connect, so it comes straight off. Have a bucket or rag ready, because whatever is in the line comes out of that port.
Run the pump for 5 to 15 seconds. Turn the pump on and watch the outlet port. You want to see liquid pushing out of it. That fully wets the pump and gets it primed.
Turn it off and reconnect the outlet hose. Push the fitting back on and make sure it's in all the way.
Run your pump. You'll still have a bunch of air in the line. It takes about 2 to 3 minutes for that air to push all the way out the end of the hose, so give it time before you decide it didn't work.

If the air won't clear

If you've primed the pump, given it a few minutes, and you're still getting air, you have a leak somewhere on the suction side. A leaking fitting on the mixer is a common one. Work back through every fitting between the tanks and the pump, making sure every clamp is tight and every fitting is sealed. Tracking down a leak takes time, but the system won't run right until you find it. If your plumbing is old and brittle, it may be time to replace it, and our Complete Soft Wash Plumbing Kit for 12V Pumps has the fittings and hose between the pump, tanks, and mixer. We cover how all of it fits together in How a Soft Wash Mixing System Actually Works.

Watch out for debris in your tanks

Any time you drill into a tank, you get little chunks of plastic, and those get pulled into the suction line. Vacuum the tank out completely after drilling, before you ever run the pump off it. Every pickup line should have a slotted PVC pickup filter on the end of it, like the one in the bottom of the tank in the video.

Even with a filter, tiny pieces of debris can still make it into the pump. A dirty tank, or one that didn't get fully vacuumed out after drilling, can cause your 12V pump problems too.

When it's the pump

These pumps don't last forever. If you've primed it, checked your fittings, and your tanks are clean, the pump may just be at the end of its life. Bleach is hard on every 12V pump, and our Rig Maintenance Guide covers what to expect and how to get the most life out of one. The habit that matters most is rinsing the pump with clean water after every job, not just at the end of the day. We go into why in 12V Soft Wash Pump Setup: Why Most of Them Die Early.

If you do need a replacement, the FloJet 6 GPM 12V pump is what we run on our builds, and the Plate Mounted FloJet 6 GPM Soft Wash Pump comes pre-wired on an aluminum plate if you want to swap the whole assembly.

Just don't skip the simple stuff. Before you start pulling everything apart, pull the outlet hose and let it prime up.

Parts mentioned

FloJet 6 GPM 12V soft wash pump
Plate Mounted FloJet 6 GPM Soft Wash Pump
FloJet QC hose barb and FloJet slide clips, if a pump fitting is cracked or a clip is missing
Bleach slotted PVC pickup filter
Complete Soft Wash Plumbing Kit for 12V Pumps
All 12V soft wash pumps and parts

Frequently asked questions

Why won't my 12V soft wash pump prime?

Most people hook up a 12V pump and never prime it. Sometimes it primes on its own, sometimes it doesn't, and a pump that's been running fine can lose prime after you reinstall mixer parts or hoses or run a tank dry. When the pump head is full of air, it can run without pulling solution out of the tanks. An empty tank, a pickup filter that isn't fully under the liquid, a leaking fitting on the suction side, or debris in the pump can all cause it too.

How do I prime a 12V soft wash pump?

Make sure your tanks have liquid in them and the pickup filters are fully submerged. Disconnect the hose from the outlet side of the pump, turn the pump on, and run it for 5 to 15 seconds until liquid pushes out of the outlet port. That fully wets the pump. Turn it off, push the outlet hose back on all the way, and run the pump.

How long does it take for the air to clear after priming a soft wash pump?

About 2 to 3 minutes. You'll still have a bunch of air in the line after you reconnect the outlet hose, and it takes a few minutes to push all the way out the end of the hose. Give it that time before you decide the prime didn't take.

I primed my pump and it still pulls air. What should I check?

You likely have a leak on the suction side. A leaking fitting on the mixer is a common one. Work back through every fitting between the tanks and the pump and make sure every clamp is tight and every fitting is sealed. The system won't run right until you find it.

Can debris in my tank cause soft wash pump problems?

Yes. Any time you drill into a tank you get little chunks of plastic that get pulled into the suction line. Vacuum the tank out completely after drilling and run a slotted PVC pickup filter on every pickup line. Even with a filter, tiny pieces can still reach the pump, so a dirty tank can cause problems too.

When should I replace my 12V soft wash pump?

If you've primed it, checked your fittings, and your tanks are clean and it still won't run right, the pump may just be at the end of its life. These pumps don't last forever, and bleach is hard on all of them. Rinsing the pump with clean water after every job is the habit that gets the most life out of one.

Written by

Tim Cray

Owner, Expert Power Wash

Tim and Kristina ran their own pressure washing company for more than ten years on trailers, box trucks, flatbeds, vans and skids before Expert Power Wash started building equipment for other contractors. Today EPW has 300-plus builds working in the field and services pressure washing rigs in the Oregon City shop every day.