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[wissel12]

I was wondering what to set the strap on aquastat at for the backup heat.  I got it wired in to the oil burner. I have it set at 150 right now.
I had it set at 140 and the burner came on. I kept turning it down(as in a lower number than 140) I thought that should shut it off. I turned it the other way higher temp(150) and it shut off. Can someone explain this to me??  I must not be understanding how it works

[RSI]

It sounds like you have it hooked up backwards. There should be 3 screws. One is common, one is NO and the other is NC. Move the wire from NC to NO.

[slimjim]

No RSI, you misunderstood the goal, he has it on the incoming wood boiler loop to monitor it's temp, when the wood boiler drops in temp, the aqua stat makes contact and allows the oil boiler to assist or take over the heat load by completing the b-1 circuit on the oil boiler, I usually set it at 160 degrees but if the wood boiler is run cold as many of you folks do it may need to be turned down a bit to keep the oil burner from firing, I run at least 190  with a 5 degree differential at the wood boiler.

[wissel12]

Does the aquastat have to be on only on copper?

[slimjim]

It will give a better reading strapped to copper, then black iron and does not work well on pex, try insulating the bulb area from ambiant temps or drafts if you think it's not very accurate.

[wissel12]

All my lines are pex. Know what should I do?

[slimjim]

Another reason that I don't like pex! At this point strap it on and hope you get a good reading, duct tape the sides to keep ambiant air from getting at the probe

[willieG]

i have found that with my heat gun if i ( as suggested by others)  wrap the pipe (no matter what  it is) with black "electricians tape" for about 4 inches i get good readings (once you adjust for different material)  my copper pipe wrapped with tape in the home is within 1 degree of the thermometer at the boiler...my wrapped pex lines are exactly 10 degrees less on a consitance basis. i have come to the point that i feel i CAN trust these readings.