Test pump on riello rdb burner for pressure?

Is there any specific way I can test the pump on a riello rdb burner to see if it giving ample pressure without an actual pressure gauge? Only my burner was working fine for a couple of days, now it won't light. After a process of elimination I've come down to two things; its either the nozzle or the pump that's gone busto. Before I buy a new nozzle though I just wanted to make sure it wasn't the pump. I did clean the filter screen in the pump but that didn't make any difference (though it did have a thin film of black gunge on it so perhaps there is a blockage somewhere).