02-658-9 Me. Code R. § 10
A solid fuel boiler must be provided with a power failure by-pass and valve in a closed system.
To prevent overheating conditions during a power failure, a normally open zone valve must be connected to the largest heating loop in the system above the level of the boiler. A manual by-pass valve must be installed in case of the failure of the zone valve. This shall be accomplished by installing the zone valve prior to the flow valve and connecting it to the largest loop in the system. The hand valve must be installed in a loop around the zone valve as illustrated in Figure 9-1.
Section 9.10.2 does not apply to listed outdoor solid fuel burning central heating appliances.
Section 9.10.2 does not apply to solid fuel burning appliances for which the interruption of power will arrest combustion and interrupt fuel supply if the appliance is a residential-type heating appliance as defined in NFPA 211
02-658 C.M.R. ch. 9, § 10