My generator ran last night but shut down before power was restored. I looked at the generator this morning and seen there was a UF alarm. This generator is less than a year old and there was hardly any load on it last night. Should I contact a repair man or wait to see if it happens again?

Most of time, diesel generator runs abnormally because of battery long time no maintenance or the deviation between components . In reality, it can be back to normal as long as you make a little adjustment. Therefore, we should have the ability to deal with the faults. For the failure of diesel generator, first you should have a adjustment and check whether it is helpful.

Maybe you can get help from the following articles:
https://www.dieselgeneratortech.com/diesel-generators/simple-ways-to-deal-with-diesel-generator-failure.html
https://www.dieselgeneratortech.com/diesel-generators/why-diesel-generator-fail-to-start.html

Sounds like a fuel issue.
Check that you have fuel left in the tank can evaporate.
Also that the filter is getting fuel by looking that there is fuel in it.
And make shore also that you are using the correct fuel if it is a 2 stroke it need 2 stroke oil added to the petrol.
Is it Unleaded petrol or Diesel is also something to check you have used the correct one.
Sounds silly but easy errors.
I did it to a diesel car put unleaded just about to start it when I realised. If I started the car It would have lasted 5 minutes and cost $10.000.00 AUD + to repair.
Got it towed and the fuel drained total cost $150.00 AUD
Regards Craig

THAT DEPENDS ON YOU'R WARRENTY.HOW MANY TIMES CAN YOU BRING IT BACK AND IF YOU USE IT THE 2 TIME IT MIGHT GET WORST AND YOU'LL BE WITH OUT A GENERATOR FOR A LONG TIME MAYBE,I WOULD ASK THE PERSON IF I CONTINUE HAVING THE SAME PROBLEM CAN I BRING IT BACK AND GET A REPLACMENT..REMINDER GO TO YOUTUBE AND TYPE [ what can I do with ALTINATOR you might like? ]