Wagner Procoat airless sprayer no longer primes possiblely due to the red power selection knob being defective. Connecting the garden hose to test the switch on "Prime" mode should have water diverting to the smaller bypass hose but it didn't. It's over a year old and out of warranty. How do I test if it's the switch?

Was the unit purchased new or used? The price of a new is about $125-170. This unit is for homeowner occasional use, not for large jobs.Was the unit working on the previous use? If so were the cleaning instructions followed and not shortcut. If paint is failed to be totally removed on cleanup it will dry inside unit.There are very few replacement parts for this unit. If the unit is not working take wrench and try to remove prime/spray valve. You will have to remove knob to access this part.

I haven't much experience with airless sprayers but I have heard the bad language from those who use them.

I expect there is still paint in the business end of the mechanism and an air bubble stuck between that and the new paint fill.

I think the sprayhead will have to be removed or dismantled so the air will be able to escape and allow priming to take place. I suggest spending a little time with the instruction manual.

Your Wagner 1250 is a diaphragm airless sprayer, which uses hydraulic oil to push the diaphragm, so the oil must be hydraulic quality as it gets quite hot; don't use any other type. The Wagner part number for their quart size is 0088009

The inlet valve is probably stuck. It is a flat poppet type, so you need to free it up. A Graco dealer should be able to supply a special small plastic bottle with a special top filled with their Pump Armour to do this job. Otherwise you can unscrew the inlet valve from the cup side to clean it out, but be careful not to lose the small spring. You should always flush Pump Armour through the ProCoat after use otherwise the passageways corrode

You either have a stuck ball valve, or a leak in the paint suction

YOU HAVE A STUCK INLET BALL
Have the unit in water, pressure relief valve turn the machine on and tap with a hammer at the inlet ball, This frees it up 90 of the time.
Otherwise the machine need to be disassemble

Most of the time when a unit will not prime it is because of a stuck inlet ball, I would put the intake in water turn the machine on to bleed. Then tap the machine where the paint comes in. 90% of the time this will get it going. Sometime you can stick a screw driver into the inlet ball and free it up. If this doe not work you need to take the machine apart and cleanor you have worn out packing.

Joe

All airless sprayers are on-demand pumps. The two settings are prime and spray. When it is set to prime, the pump will draw liquid from the bucket below and pump it out the side tube and will never stop until you switch it back to spray. When set to spray, the pump will run until the pre-set pressure is reached, then stop. As soon as you start spraying, the pump will run until a few seconds after you stop spraying. Tip size and pressure setting will affect how long after you stop spraying the pump will run. A large tip and high pressure will cause the pump to run longer after you stop spraying.

Just had the same problem with the same exact unit. Here's how to fix. Turn the pressure knob fully counterclockwise. Take a 5/8's wrench and back out the pressure knob 2 full turns. Yes, the exact same knob you just reversed only get a wrench on where it connects to the unit. Run it for a minute like that. On off a couple times.Run the gun and get the air out. You should notice it working. This is per the owners manual. Good luck man.

I worked at a tool rental center when I was going to college and learned many useful tips / tricks about airless sprayers. Airless sprayers have two check valves/balls that can stick on their seats or stay open due to chips of paint on seat. Easy method to prime is to remove intake filter from machine, tilt the machine back far enough so that the pick-up tube is pointing up high enough to pour water in tube until full; hold in this position and turn on machine. If water is sucked in turn off machine and tilt machine into pail of water and restart to check for prime. If it still will not prime remove water from pickup tube and use air pressure into tube with bypass valve open. Air pressure will attempt to release the stuck lower check ball. If air pressure does not release stuck ball you may have to use physical pressure against ball. If lower check ball was stuck you can assume that the upper check ball is probably stuck also. An aid to loosen stickey valves is to pour solvent into pickup tube with machine tilted back as before leave overnite. Enjoy