We've had a similar problem. the tip of our wand would arc on any grounded metal. If you touched any metal connections on the hoses you got a good current. For us, our burner wasn't grounding at one point, and at another time it was merely grime build up around the outlet on the generator that was creating a curcuit to the pw frame to the hose, and grounded by us or any conductor touched by the pressure tip.
It might help to check anything that creates electricity (generator, battery recharge, battery). You may have a funny connection. Play with a voltage meter and see if you can isolate when it's charged (while machine is on w/ or w/o heat, or when everything is off).
Happy Hunting!