I service machines and do the following.
Strip and clean wand valves filters and jets.
Check hoses for poor connectors and hose crimps.
Check exterior of mc for cracks etc
Wash out and clean waste tank.
Check and clean waste tank air filters.
Remove dump valve and check seals.
Clean solution tank and check inlet filter.
Check heater and thermostat function.
Fill enough to run and check pump pressure at no flow and with 1/2/4/ jets.
Empty machine.
Open mc to access motors and visual for leaks and drips.
Visual check wiring state.
Switch on motors and check vacuum level.
Remove vac hoses and vac units.
Remove covers and brushes.
Blow out carbon deposits.
Inspect commutator coppers.
Replace brushes and covers.
Remove first stage vac unit cover and inspect and clean centrifugal vanes.
Replace motors and pipes.
Remove pump and check pipe connections.
Open motor brush end.
Blow out carbon and replace brushes and end.
Remove pump head and clean pump chamber inspect flap valves, pressure relief valves and springs.
Replace pump head.
Replace pipes and pump.
Renew any bad electrical connectors and wiring.
Close machine and check vacuum levels and pump pressures.
PAT test.
Clean and polish exterior casing.
Write invoice.
Parts that are past their best are renewed as required.
Depending on the machine this lot will take from 1 1/2 to 2 1/2 hours according to how awkward acess is. Some are a lot better than others.
Trevor