Combi Boiler

Hi everyone, Looking for some help as I am at my wit's end. I needed to shorten a baseboard on my 1 zone baseboard heating system so though the advice I got in [url=https://www.doityourself.com/forum/boilers-home-heating-steam-hot-water-systems/638687-shortening-baseboard-please-confirm-my-plan.html]this thread[/url] I added a combo [url=https://www.supplyhouse.com/Webstone-50613-3-4-Sweat-PRO-PAL-Full-Port-Ball-Valve-w-Drain?utm_source=google_ad&utm_medium=Shopping_tm&utm_campaign=Shopping_TM_HPLTV&gclid=CjwKCAjwsfuYBhAZEiwA5a6CDN9IuTRhpuwW7Iw_BNK7R_ATV4r5qIZdz3obAkyVfV1GoJ0x-Pd2rhoCbv0QAvD_BwE]shut off/purge valve[/url] on the return line and a regular shut off on the supply line. The goal was to give me a way to purge air without having to drain the boiler. My boiler does not have a fast fill valve so it took many hours to get the water flowing smoothly out of the hose I hooked up to the new drain valve. Problem is that wasn't enough - heat was insufficient. So I bled at the baseboards again, and again, and again - only one is a smooth stream with no air. To make matters worse, my circulator pump got very hot and buzzed twice when called for heat. I shut down the thermostat to let it cool. I am thinking maybe it is caused by air not cooling the pump? Bottom line is I cannot seem to get the air out of the system. I have purged the at boiler through the new drain at least 50 times and the radiators about the same. Any advice?

Been in our 2 story house 25 years. Same hot water boiler that came with the 50? year old house when we moved in (it's not the original boiler). As much as I am pretty handy and have insulated the attic, pipes, etc, we've woken up in the morning 2x in the past 3 years (and none before) - (1 time 3 years ago and 1 time a couple weeks ago) where the 1st floor zone appeared to be frozen after a 5 - 10 night outside. Neither time was there any cracking of the pipes. The day warmed up and that zone started working again. Each time I've found embarrassingly glaring issues with air coming in and fixed them (it IS great when it's really cold outside - finding leaks is EASY : ) We typically have our setback thermometer keeping the 1st floor in the upper 50s overnight. I guess on the cold nights at least, we need to turn that up a little. But I wonder - is there a way to get the recirculating pump / that zone to come on 2 - 3x overnight - every night or when we flip a switch for that night. I'm thinking keeping the water circulating would keep the water from freezing? Or any other ideas you'd offer? There's a fair amount of areas in the basement where I can't get to the radiator pipes to insulate them / make sure there's no air leaks near them. (finished basement, HVAC ductwoprk, etc.) THANKS!