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[smithbr]

Okay.  So everything's running fine, except every now and then, we get a water temperature rise.  This morning, we went from 190 to 193, an hour after the last warmup (see attached chart).  I'd attribute it to a stuck primary valve, but it's not stuck, and the rise doesn't happen right after a pulse (which is what happens when the valve does stick, as I've seen it happen).  Instead, this time it was 6 minutes after the pulse, AND happened in about 2 minutes.  It's like we've suddenly put heat back into the loop from the house.  Patently impossible, but  there it is.
Anyone seen this, and figured it out?  Is my pump failing (and how would that cause this?)  Is there something else going on with the primary or secondary solenoids?  I can't think of anything else that would cause this.

[E Yoder]

3 degrees doesn't seem like much, could be a warm spot in the tank moved a bit.  Depending on your flow through the tank it can vary quite a bit if stratification is going on.

[smithbr]

I guess I'd buy that, if it was a bit more random, but I don't have any other explanation.  Thanks for replying, anyway.  This forum is dead!

[bjp]

Could there have been some strong wind gusts at the time that created a draw through the stack?

[Pointblank]

Thats unusual for sure.... Was it just a one time only thing or is it repeating?  Maybe the pump airlocked for a bit? Temp sensor is reading erratic?
If the pump is old, sometimes the impeller starts to disintegrate and causes problems.
Is it still reliably delivering heat to the home?