Hot water pressure after vacation

I live in a 3 year old home and have a gas hot water tank.

Never had any problems with the hot water until earlier this year after returning home from a week's vacation (house was empty while I was away) - when I noticed that the pressure in the hot water faucets all over the house was very low. This continued for a couple of days until it fixed itself and the pressure returned to normal.

Now, I have just come back from a 2 week trip and am having the same problem. There is hot water, but it comes out of the faucets and shower at less than half of its usual pressure. This has been going on for the last 4 days. There is no problem with the cold water.

Can anyone suggest what the problem might be? It only happens after the house has been empty for more than a few days, and has only started to happen this year.

Any help would be appreciated. Thanks!

There is often a heat trap installed on the WH. SOme use a plastic ball. It could have some crud in there, and it is acting like a plug. Eventually, it clears up and can move, allowing normal flow.