I have an H machine with around 25000 hrs. failing OLC test. I watched it for a while and noticed the conductivity will fluctuate every 15 seconds. In about 1 second it will go from 14.0, 14.3, 13.7, 14.0, then stabilize for 15 seconds again. I have a feeling that this is why the OLC is failing I just haven't seen this before.
Any Body Know why this would happen? Otherwise it works fine. It doesn't alarm when it does that or anything.

There could be a couple of different problems. If cond is fluctuating check the b/c membranes and the heat exchanger, might check the cond cell Please post the final outcome, so we can all learn from your experience

try doing a conductivity cell calibration. i've seen this solve my problems alot of times.

Thanks all,

I will try those things and let you know. It is due for an annual anyway so it will work out perfect!

I would try to calibrate the acid and bic pumps a few times and then the cells. Also, check your degas dac. If set too high it could cause electrical noise.

Just an update on this situation. I performed an annual pm because it was due for one and I didn't notice anything out of the ordinary. It passed all test and worked fine. I put it back in sevice and haven't had a problem since. I wish I could give a better answer but it could have been anything from a bad o-ring to pump calibrations. Anyway, thanks to all for you support and advice.