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Testo 320 problems

Dan C.
Dan C. Member Posts: 248
I've had a Testo 320 for about a year or two now. I really like it. Recently it stopped giving me a CO reading. When it does give me a reading it's very low. Most recently I did a test and the CO Reading was 9ppm. They then had mass save come out and do a combustion test for heat loan and the readings were over 100 ppm. I bought a new CO sensor and changed it. I went back to the same house today and I am now getting a reading of 0-1 ppm. Is there anything else I can do? Or do I have to send it back? The whole reason I bought this unit is because the sensors can be replaced and I thought I wouldn't have to send it back all the time to get calibrated.


  • Tim McElwain
    Tim McElwain Member Posts: 4,628
    Testo has a NOX eliminator which will give you much lower CO readings. Make sure you are using the COAF reading which will be the higher reading of the two CO readings.
  • Dan C.
    Dan C. Member Posts: 248
    They are both had zero sometimes air free is at one. But the strange thing is if I start my truck and check the exhaust it spikes the meter.
  • captainco
    captainco Member Posts: 796
    What was your O2 reading? Hard to tell if you have a leak or a weak pump without both readings. Take a match and hold it at the end of the probe for 1-2 seconds. The CO reading should be over 200ppm.