Condar thermometer keeps losing calibration

My Condar catalytic probe thermometer seems to keep coming our of adjustment. The bottom end of the scale - 2 small tick marks below the lowest large tick mark - seems to represent 60 degrees; so the needle should be near that lowest small tick mark when the stove is dead cold. So I adjust it by loosening the nuts and rotating the scale. But then after a few fires it'll drift to where it's a couple hundred degrees' worth below there - far enough that the 500 degree reading (where you want to engage cat) is WAY off.

I tried calling Condar but got pretty much blown off (I think). The receptionist first asked me when I bought it and said well the warranty is only one year, so I just need to buy a new one. When I persisted, she said I could send mine in for a "repair", but got pretty evasive when I asked what could be broken to cause this problem ("maybe the weld is broken", really ?).

Anybody else had this problem ?

pen said:

When you decided to recalibrate it, was what it was giving you readings during the "active" part of your burn that were reasonable?

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Yeah, I guess. When you're in the active zone, where reasonable reading can range over maybe a 1000-degree range, the readings could be reasonable even if the thing was 200 degrees off. My main concern is actively measuring when the cat is at 500-degrees and it's time to engage the cat (close the bypass); when the thermometer is off by as much as 200 degrees, that's a problem. Though it's always off in the same direction (the needle is 100-200 degrees below the 60-degree mark), so if I'm reading 500 degrees, certainly the cat is active, but then I'm waiting TOO long to turn it on. Mainly it just annoys me that I can't have the thing be calibrated.

31 bertram said:

Hmmm, I was getting ready to order the same stuff from them, very interested to see what happens

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I don't think anything is going to happen. I wonder if there's an alternative product ?

Stump shot said:

I rarely use the catalysis thermometer to determine when to close the bypass. It is to slow to react. The two pictures were take on a cold start. The stove top first then the combustor as fast as I could.

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Damn, that's kinda amazing. I have to say though, I think you are experiencing EXACTLY the effect I'm describing. That is, I believe that if you had the version of the thermometer with actual degree readings on the scale, and if the stove was cold, it'd be reading about MINUS 200 degrees (if the scale went down that far). So it's really showing 500 degrees or more in the photo. I might be wrong, but next time the stove is cold, see if the needle is not well below the bottom of the "Inactive" zone (not at the bottom, as I believe it's supposed to be).

If the combustor is glowing it is active.

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Sure, but is the other thing the case: if the converter is active, must it be glowing ? And I'm pretty certain that's not the case.

Thislilfishy said:

Pretty safe bet that a bimetallic spring will be fairly inaccurate at the extremes of its range.

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Yeah, I hear ya', but I'd still think the "zero" (not "zero", but "cold") would be somewhat reproducible.

My flue therm also no longer goes back to zero either, but measures relatively accurately at 400 ....

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How do you know it's relatively accurate at 400 ? With an IR gun ? Is the flue therm a spring too ?