Ensure the test area is reasonably free of VOC’s, for example by moving the instrument through several locations. The span gas portion of the custom calibration may be inaccurate. Set the instrument to factory calibration and see if the response continues to over-range. If it does, then ensure there are not high levels of VOC present in the ambient air. Remove lamp and clean, blow out cell and re-calibrate.
Contact your local Authorised Service Centre or email: firstname.lastname@example.org.