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Old 11-08-2011, 09:52 AM   #1
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boiler temp overshoot

A while back, I noticed that my boiler seemed to be running about 20-25 too hot. With the aquastat set at 180/160, the temp gauge would read about 200-205 (or sometimes even higher) after a burn cycle.

Before resorting to a new aquastat, I tried a couple other things first. I replaced the combo gauge to make sure that it wasn't just reading high. I then pulled the aquastat and temp bulb well to make sure the bulb was fully seated and the well wasn't scaled up or anything. No change - temp was still high by about 20-25.

As a temporary measure, I turned both controls on the aquastat down by 20 (160/140), and that seemed to work ok most of the time.

I then bit the bullet and installed a new aquastat. To my dismay, even with the new aquastat, the temp still seems to be high by about 10-15.

A couple questions:

1) Is it worth replacing the temp bulb well? The inside (wet) surface didn't have any scale buildup, but I've since read that over time they can develop a glaze/coating that impedes heat transfer.

2) Is it worth applying heat transfer compound to the bulb & well? I know there are different opinions on this: some say you should always use it, others say don't bother.

Any advice or info will be much appreciated.


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