You switch the sprayer on, the motor runs, the pump cycles and nothing comes out. Or paint creeps up the suction tube and then stops. It is one of the most frustrating moments in a painting project, because the machine sounds like it is working. The good news is that a sprayer that runs but will not draw paint is almost always letting air in or failing to seat a valve, and both problems are usually cheap to fix.
Before you spend money on a new pump or a new sprayer, work through the checks below in order. They follow the troubleshooting tables in the manuals for Graco’s Ultra, 390 and Magnum sprayers, which list the same short set of causes. The order is simple: cheapest and quickest first.
Key takeaways
- Most priming failures are an air leak on the suction side, a clogged inlet strainer or a valve that is stuck or not seated.
- Check the prime valve position, the paint level and the inlet strainer before anything else.
- Do not let the pump run dry for more than about 30 seconds. It can damage the packings.
- Always relieve the pressure before you loosen a fitting or take off a strainer.
- If every cheap check passes, the next suspects are the inlet valve and the packings, not the whole sprayer.
How an airless pump primes
An airless sprayer uses a piston pump. On one stroke, paint is drawn up the suction tube through a one-way ball valve at the bottom of the pump. On the other stroke, a second ball valve in the piston lets the paint pass to the top of the pump and out to the hose. Packings seal the piston and the rod so that the pump can build pressure rather than leak it.
Priming is simply the process of pushing the air out of that system and replacing it with paint. A small air leak anywhere on the suction side lets the pump pull air instead of paint. A ball that is stuck or cannot seat means the pump cannot hold a column of paint between strokes. Either one stops the sprayer from priming.
Safety first: relieve the pressure
An airless sprayer stays pressurized after the motor stops. Before you loosen a fitting, remove a strainer or open the pump, turn the machine off, lock the gun and follow the Pressure Relief Procedure in your manual. Fluids under pressure can pierce skin and look like a small cut while causing serious injury, so never put a hand over the tip or the gun. Treat every check below as service work.
The eight checks, in order
Check 1: Is the prime valve in the right position?
To prime, the prime valve (called the prime/drain valve on some models) should be open, which is usually the down position, with the drain tube in a pail. Graco’s Ultra manuals say to leave it down until fluid circulates through the drain tube for about 15 seconds before you switch to spray. A very common cause on Magnum-type machines is simply a valve left in the spray position. Make sure it is set correctly and that the drain tube is not kinked or blocked.
Check 2: Is there enough paint, and is the suction tube in it?
It sounds obvious, but a nearly empty bucket or a suction tube that is not fully submerged pulls air. Top up the paint and make sure the inlet is well below the surface. Do not let the pump run dry: Graco warns that more than about 30 seconds without fluid can damage the packings.
Check 3: Is the inlet strainer clogged?
The strainer on the bottom of the suction tube catches debris before it reaches the pump. When it clogs, it blocks the flow. Relieve the pressure, take the strainer off, rinse it and look at the mesh. Graco’s tables list a plugged inlet screen as a cause of hard priming. If the mesh is torn or stained solid, replace it. Replacement inlet strainers and filters are inexpensive compared with the time lost chasing a bigger problem.
Check 4: Are all the suction-side connections tight?
This is the most common hidden cause. Air can enter anywhere between the paint and the pump: the strainer, the suction tube joints, the fitting where the tube meets the pump, or an o-ring that has hardened. Tighten each connection and replace any damaged o-rings or seals. On some models, Graco also tells you to check the swivel o-rings on the suction hose. Graco’s procedure for a hard-to-prime pump is to tighten all fluid connections and cycle the pump as slowly as possible while priming.
Check 5: Is the paint too thick?
Paint that is too thick for the sprayer will not flow up the suction tube. Thin it within the coating maker’s limits. This is especially common after a cold night or when a can has been open for a while. Stir and strain the paint before you start.
Check 6: Is the inlet ball stuck?
If paint has dried in the intake valve, the ball can stick to its seat. Graco’s FAQ for its Magnum sprayers suggests removing the suction tube and freeing the inlet ball with a pencil. For other models, the manual tells you to clean the intake valve and check the ball and seat for nicks. A seat with a nick, or a ball that has picked up dried paint, will not seal.
Check 7: Is the tip or filter blocking the flow?
A clogged spray tip, gun filter or outlet filter can make the sprayer behave as though it will not prime, because the paint cannot get out. Relieve the pressure and clear the tip, the gun filter and the outlet filter. This is one of the quickest checks and it is easy to overlook.
Check 8: Are the packings or the piston valve worn?
If all of the above are fine, the pump itself may be the problem. A leaking intake valve, a piston valve that is not seating or worn packings are all listed by Graco as causes of a pump that is hard to prime. This is where a repair kit comes in. Before you open the pump, identify the pump model and make sure the kit you order matches it.
A quick reference table
| What you notice | Likely cause | What to do |
| Drain tube never fills, pump cycles | Prime valve in wrong position; air leak on suction side | Set the prime valve down; tighten every suction connection |
| Paint comes up the tube, then stops | Clogged inlet strainer; thick paint; low paint level | Clean the strainer; thin paint; top up the bucket |
| Pump runs fast, no pressure | Stuck or leaking intake ball; piston valve not seating | Free or clean the ball; check seats for nicks |
| Paint leaks at the packing nut and priming is poor | Worn throat packings | Replace packings; do not over-tighten the nut |
| Sprayer primed, but nothing comes out of the gun | Clogged tip or filter | Relieve pressure and clear the tip and filters |
Two special cases
A sprayer that has been stored in the cold
If a sprayer has sat in a cold garage with paint or water in the pump, it may be frozen or partly frozen. Graco’s manuals say to thaw the pump completely before starting it. Starting it while frozen can damage it. If paint dried in the pump, they say to replace the packings.
A sprayer that primed yesterday and not today
This usually points to a slow air leak or a part that dried out overnight. Check that the pump was flushed and stored properly last time, that the inlet strainer is clear and that the suction connections are tight. Dried paint on the inlet ball is a classic cause.
Do not replace the whole sprayer yet
Many people decide that a sprayer that will not prime is finished. In most cases it is not. The parts that fail in these situations are inexpensive: a strainer, a set of o-rings, a ball and seat, or a set of packings. Replacing the whole machine for a clogged strainer is an expensive way to find out you did not need to. If you want a longer walkthrough with the part numbers for common models, the full guide is at.
How to prevent priming problems
- Flush after every jobwith water for latex or mineral spirits for oil-based paint, and use pump protection fluid if the machine will be stored.
- Strain the paintto keep lumps out of the intake.
- Clean the inlet strainerwhenever you clean the gun filter.
- Replace o-rings and sealswhen they look hard, cracked or flattened.
- Keep spare parts handy:a strainer, o-rings and a repair kit cost little and save a lot of time.
Frequently asked questions
How long should an airless sprayer take to prime?
Usually a short time once everything is set correctly. Graco’s manuals describe letting fluid circulate through the drain tube for about 15 seconds before you switch to spray. If paint has not come through within about 30 seconds, stop, relieve the pressure and check for an air leak or a clog. Do not keep running the pump dry.
Why does my sprayer lose prime in the middle of a job?
The paint level may have dropped below the suction inlet, a connection may have loosened, or a ball valve may be sticking. Check the paint level first, then the suction connections and the inlet strainer.
Can a worn spray tip cause a priming problem?
A worn tip does not stop the pump from priming, but a clogged tip can stop paint leaving the gun. It is a good idea to check the tip and the filters as part of the diagnosis.
When should I replace the packings?
When paint leaks at the packing nut or down the pump body, when the pump will not hold pressure after the cheaper causes have been ruled out or when the pump has been through a frost with paint in it. Graco does not publish a packing life in hours or gallons, so replace them when the symptoms say so.
The short version
Work down the list: prime valve, paint level, inlet strainer, suction connections, paint thickness, inlet ball, tip and filters, then packings. Most sprayers that will not prime are fixed in the first four steps for the price of an o-ring or a strainer. Take your time, relieve the pressure before each check and test after each change.
About the author
The eRepairCenter parts team helps painters, contractors and maintenance crews identify and replace worn parts on airless paint sprayers. eRepairCenter is a Houston, Texas supplier of aftermarket, used and surplus replacement parts and an authorized Bedford Precision distributor, shipping across the United States.
