slabadie wrote:You suggested that I start at a lower temp and watch how far the water temp over shoots. Is there an ideal top end? I have my diff. at 5 but the circulator doesn't come on until 10. I am not sure it the aquastat is defecctive or not. I fear if I set it to a diff. of 10, the circulator won't come until 20 past the setting.
The differential refers to the difference in temperature an aquastat will wait for until it reactivates.
For a 4006B set at 180 with an 8 degree differential , it will close the contacts as the water rises to 180. It will not open the contacts until the water has dropped to 180deg - 8deg = 172 degrees
For the 6006A it is a little different since it is a double-throw aquastat. This is directly from the Honeywell manual:
When there is a drop in water temperature (to dial
setting, less differential), the R to B contacts make
and the R to W contacts break, preventing circulator
operation. When there is a rise in water temperature
(to dial setting), R to B contacts break and R to W
circulator contacts make.
Your fan should be on the RB contacts and the circulator between the two boilers (if there is one) should be on the RW contacts. The differential has NO effect on when the fan turns OFF, only for where the fan turns back ON
You still didn't clear up which of the 3 aquastats is controlling the fan. It should be the L6006A that is in the boiler, not the strap-on that was added as a "backup". Think of the combustion fan as a oil burner gun, it should come on when the water temp in the boiler drops and shut off once the temp is met.
As for idea water temp, the ideal temp is hot enough you can deliver enough heat to the house on a cold day but not so hot you're boiling the water. But for now just pick something in the middle - like 170deg. If you can get the boiler to maintain a desired temp you can then adjust it to your needs.
Would a little ascii art help? I had a hard time with this until I sketched it on paper.
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Using 4006B @ 180 w/ 8deg diff, 6006A @ 160 w/ 10deg diff
180 - 4006B contacts close (turns on dump zone)
172 - 4006B contacts open (turns off dump zone)
170 - TARGET TEMP
160 - 6006A RB (FAN) contacts open (turn off), RW (Circ) contacts close (turn on)
150 - 6006A RB (FAN) contacts close (turn on), RW (Circ) contacts open (turn off)
You also need to make sure the aquastats don't "fight" each other, meaning the fan should never be able to run when the dump zone is triggered.