How to sum a column of hours:minutes values

I want to total a column of Hours:minutes values.

If I use a1+A2+A3 etc, it works if I format the cell in which I want the total to appear as [HH]:MM:SS

But if I use the SUM function for a range of cell (much more convenient) I get the answer 00:00:00.

Is there some other function I should be using or is this a bug?

This is to total a series of glider flight durations express as hours and minutes, to get a total number of hours.

Possibly the source cells are actually not dates, but text formatted as dates. The plus converts them implicitly, but SUM cannot.

I tried formatting the source cells as [hh]:mm as well but same result.

and does the source cell format change when you do that?

Please post a sample document to some share and post a link here to check

I don’t think it did, but how can you tell?

I think I have solved the problem myself after reading Mike’s comment.

The list of times was imported from a csv file - ticking the option “detect special numbers” at the import stage seems to make the SUM function handle them correctly, as long as the total cell is formatted [HH]:MM:SS

Thanks Mike Kaganski