Water flows for about 10 seconds through my wand and then the flow stops and unit begins to build pressure. The trigger has a ton for pressure but no flow to the jets. The only flow I'm getting is the return to the water box from the regulator. When I shut off the machine and key the trigger I here back pressure going into the heat exchanger coils. Any idea what this might be? The pressure gauge is also spent. After the machine sits for a while same thing happen again. Could this be a check value, y strainger or faulty accumulator? Could I possibly need descaling? Unit is a ProChem Oilfired.