Vaporstat Installation

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Horizontal (roll) leveling is much more critical because the control's scales are calibrated to the weight of the mercury in the bulb, and the bulb is oriented on this axis. If the control is not level, there will be too much or too little mercury in the right part of the bulb, therefore too much or too little weight, therefore the switch won't cut in and out at the expected pressures.

"Pitch" isn't anywhere near as critical. As long as you're close to level, you're in good shape. The recommended way to install these guys on a siphon loop is so that inevitable exapnsion and contraction in the loop would cause the control to slightly move on this axis. If you can see through the loop while you're looking at the front of the control, you've got a problem.

James Bates

I installed a Honeywell L408A vaporstat 2 days ago and it has a pendulum in it for leveling side to side which I went by. It does not have a level for front to back. Is this adjustment critical? It functioned OK till this morning and now is turning on and off every 45 seconds until the thermostat is satisfied. I checked the pendulum and it has not gone out of adjustment. I also put a one inch bubble level that I use for leveling clocks on top of it and it shows that it is level side to side. I have the main at 8oz. and the diff. at 8oz.