Interesting. Ds, 21 months, has always loved baths as well. Just last night he refused to take a bath. He wasn't that dirty, so we just let it go, and wipes down his face and hands with a wet cloth. This is the first time it happened, so I don't know if it's a pattern yet, but dh says that ds has not enjoyed the baths as much the past few times. He has always hated getting his hair washed. He has a lot of hair, and we wash it every other bath. And he only gets a bath about 3 days a week. So we don't know if it's because he doesn't want to get his hair washed, or if he just isn't into baths right now.
I definitely wouldn't force it though. If all else fails, a warm wet washcloth would work fine, and when the weather warms up, let him run around naked with the hose!