Alan, if you disconnect the ourlet side of the impeller pump, or remove a drain on that line if you have one you should see lots of water spraying out from it Your impeller is working at least some then. Or, start with a block drain and see if water is coming out of it while you run the engine.
If water is coming out of the impeller well but not the block you may have a blockage at a heat exchanger. Just fallow the line until you have not water pressure.
Don't run the engine if you have no water in it for any length of time/