Inspect the plasma cutter's electrode if the tool fails to start, or operates only intermittently. If the electrode has a wide pit and the copper is black or blue, this may be due to a low flow of coolant. Verify the flow rate of the tool. If the flow rate is not operating at model specification, check for line kinks or leaks that may impede coolant flow. Replace kinked or leaky lines, and replace completely melted electrodes.
Check the electrode for gas contamination. If the electrode has a heavy layer of black residue, gas contamination could be preventing the torch from starting or operating efficiently. Place a clean paper towel beneath the torch while gas is flowing through the tool. Any moisture or debris could be a sign of gas contamination.
Inspect the interior of the nozzle for damage. A slot, gouge or "keyhole" within the nozzle may indicate low pressure within the plasma chamber. Check for gas line links by applying soapy water to all fittings and lines, then pressurize the lines.