Clean flange probe-probe-sample line filter-sample line line tube-diaphragm pump-filter balston from dirty of dust use instrument air supply. Test function humidity sensor and check filter humidity result function humidity sensor normal and filter humidity good condition note replace filter humidity at 443 2K1 with spare filter. Do test gas CO at 463 2K1 reason reading often -0.001 to 0.002 result reading CO 1.1 PPM ( RIZAL & ADI & EVE INDY & ANDRI & UNJ AZRIEL )