Coolant reservoir problem

Hello,

I am having a small issue over here with my daily driver. Two days ago I got my front bumper repaired because it was dislocated so might as well I wanted to do the basic routine checks inside the engine bay. We took a look at the engine oil, coolant etc. My father came to give me hand with the coolant level because I was not sure. Unfortunately, there was a storm soon coming so he closed the hood and by the time I came back to finish up the things he said it is all good. Unfortunately, he forgot to put the coolant cap back on and I have been driving around the whole day yesterday without having it on. At the end of the day before I went inside the garage I heard something weird under the hood so I immediately went to take a look at it. The coolant was boiling inside the reservoir and I just noticed that the cap was on the car’s battery. (Luckily I did not lose it.) So I waited until the coolant cooled down and I put it back on. This morning I had to take it to work and the car’s heating was not working. I had no time to check under the hood because I was in a rush. What could be the problem? Is it serious? Today I am definitely taking it to a repair shop just in case.

Thank you for your answer in advance.