Sub Zero Temps - Boiler cycling

[Johnnyf0614]

We have had a feed days straight of extreme sub zero temperatures. My oil burner cannot keep my house warm. It’s holding steady around 65 degrees even though my thermostat is set for 70. The circulator appears to be running. The pipes are hot. The baseboards are warm. The furnace is cycling on and off every 7 minutes or so even though the thermostat is not turning off. Is the sub zero temps the cause and it’s just too cold to keep up? I’m concerned about the cycling ever 7 minutes or so.

 

[Dana]

Is the boiler hitting it's high temperature limit, with short burns every 7 minutes?

Those would be symptom of low flow in the system, which could be due to air in the system or a pump impeller that is failing.

But let's zoom in on it a bit:

What is the boiler model (or just it's nameplate BTU-inpud and DOE output numbers).

What s the high-limit temperature setting on the boiler (either on the aquastat, or programmed if digitally controlled)?

What is the system pressure (there usually a temperature & pressure gauge on or near cast iron boiler, usually reported in some display or under some menu on digitally controlled boilers)?

How many feet of baseboard do you have? (Broken down zone-by-zone, if multi-zoned)?