It will start out with a good flow then will not pump any water even though it is keeping its prime.

if the water doesnt circulate, there could be many causes. start at the very beginning. does the pump sound 'normal'? if there is rattling or buzzing, the pump might not be turning and there fore no circulation. is there water in the system? even though most pumps are 'self priming', you should fill the hopper with water to prime it. are the lines open? make sure the supply to pump from skimmer is free of blockage and that the return lines to pool are open and free from blockage. if all this looks fine, then you have to get deeper into diagnosis.

Check for water flow / water flow restrictions / and water flow blockages.

Many things create water flow reductions: Dirty filters, plugged impellers, packed with debris baskets - both skimmers and at pump, closed to partially closed valves, air suction leaks: worn shaft seal, worn orings at pump lid or pump volute body, low water level, stuck skimmer weir blade/gate in the up position & skimmer empties and air is sucked into the system which may cause the pump to lose prime. This a problem that goes un-noticed and is hard to detect even by some service technicians!

Ventilate message

That means the pump needs to be primed by running water through the wand. Push the water button and open the knob on the right. You will hear the pump change tone when it primes and the light or message will disappear. If you have a restriction in the intake line the message will not go away. There is a flow meter inside the machine that measures water flow. If the flow meter does not spin when the pump is running, the computer thinks that the pump is not primed. Coffee grounds can get into the intake and restrict the flow meter. If you get a restriction in the water intake (below the water tank, on the machine) the pump may run and water comes out, but the flow meter does not create the jet of water to spin the turbine wheel to send impulses to the computer. You get the ventilate message. One thing to remember is when you are working on the water system (have the water tank off) do not fill the bean hopper and visa versa. Keep them covered when working on the other. Cross contamination will damage a machine fast
The first thing that I would check is the tip of the steam wand for a plug. If that is clear then I would suspect a clogged flow meter. If you can get the flow meter out it twists apart and don't loose the parts and the dot on the turbine goes up. Clean out the small opening on the bottom pipes where the hoses attach. Look inside and make sure that they are clear before reassembling.

To prime the pump run the hot water cycle for a few seconds, also when inserting the tank on the machine make sure it slides down the back making contact that will help the reed sensor, find the magnet in the float.

Run the hot water cycle for a few seconds to prime machine.

SOUNDS LIKE YOU HAVE A SUCTION LEAK , CHANGE SHAFT SEAL AND WHEN YOU START PUMP RELIEVE AIR OFF OF FILTER. THIS HELPS PUMP PRIME FASTER

You can't manually reset. The machine will have to do it. I had the same problem, two green flashing lights with one red (water) all 3 would just keep flashing and not turn solid. No coffee can be made or hot water. I could not pump prime. The problem was the steam wand was blocked with old milk residue. It needs unblocking or you will never pump prime. I could not unscrew the steam wand...so I let it sink in a glass full of hot water for a few minutes and then turned the water knob counter clockwise to push out the softened residue. After that, everything was good. When water started flowing out of the steam wand, the red light turned off and the green lights turned solid. The obvious answer to why you can't pump prime is there is a blockage somewhere and best to start with the steam wand. --Mabada

Assuming that you have a discharge line check valve.
Start with a full close control flow valve. Then Open and fill the priming port with water. Once full, close the priming port, and switch the power on. And then, slowly
open the control valve to appropriate level, such that it
will not break suction. Just send your e-mail for further
assistance.

1. Suction strainer with checkvalve must be always
under water.
2. Check the suction checkvalve if holds water. Water
must remain steady when primed.
3. Open the priming port, and fill it full with water.
4. Close the flow control valve.
5. Switch the power on and start the pump.
6. Then, slowly open the flow control valve, to the
level such that it will not break suction, and
stabilized the water flow..

Sounds like the water is syphoning away due to the drain outlet hose being too low..Raise the hose higher, and this should solve the poroblem.