you seem to have two seperate problems.
One....the tripping which has been sorted by replacing the vac.
Two....the loss of pressure. If you have loss of pressure at the guage then it is down to a pump problem, air locking or faulty guage. Nothing to do with filters or the wand.
If the guage registers zero when pump switched off, then that should be ok.
Turn the presure valve up to maximum, then check that there is no flow comming from the dump elbow in the bottom of the freshwater tank. If you have flow from here then bleed valve is at fualt. If the bleed valve is leaking slightly as you say then it just needs the ''o'' ring replacing or a new valve.....it should not affect output pressure if if the ''o'' ring is leaking.
Did you try bleeding air with hose into tank?
Open the machine and check for water leaking from the pump....feel under the pump head....any water, then the seals have gone. If the pump head is leaking then you need a replcement seal/piston kit from Ashbys.
Also check filter at bottom of solution tank....can't think of anything else
