Miller Millermatic 210 Owner's Manual page 42

Problem
Welding arc not stable.
OM-1325 Page 38
Probable Cause
Wire slipping in drive rolls.
Wrong size gun liner or contact tip.
Incorrect voltage setting for selected wire feed speed on
welding power source.
Loose connections at the gun weld cable or work cable. Check and tighten all connections.
Gun in poor shape or loose connection inside gun.
Remedy
Adjust pressure setting on wire feed rolls. Replace worn
drive rolls if necessary.
Match liner and contact tip to wire size and type.
Readjust welding parameters.
Repair or replace gun as necessary.