02-658-8 Me. Code R. § 6
All oil-fired boilers must be provided with a properly installed and operating low water cut-off.
The low water cut-off may be installed in, or attached to, the boiler at the level recommended by the boiler manufacturer, but in no case shall the low water cut-off be installed below the crown sheet. The low water cut-off, when not installed directly in the boiler, may be installed either in the main supply line (vertical riser) as close to the boiler as possible, or in a water column of continuous piping attached directly to the boiler.
The low water cut-off must be designed and approved for the medium used (steam or water).
No valves or other obstructive devices shall be installed between the boiler and safety controls or devices.
02-658 C.M.R. ch. 8, § 6