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My Peerless M1 boiler fails but ONLY when it's very cold
I own and live in a 12-year-old three-family house in Bronx, NY. The house was built with gas heat, PEX tubing, baseboard radiators. There are three apartments, three boilers. Alone among them, mine (ground floor) will predictably work fine until 1) the unit shuts off for the night, 2) the temperature goes below about 22 degrees Fahrenheit and 3) the system attempts to kick in. Control is from a battery-powered electronic thermostat that automatically turns the temperature to 62 at midnight, then up to 70 at about 7:30 AM.
I'm covered by a home warranty but by the time a repair person can get here, #4 in the list kicks in: The unit comes on just fine after the outside temp goes above freezing. They then are unable to find anything wrong with the system despite my description.
HELP! Thanks, guys (and gals), much appreciated.