UTH not hot enough on inside of tub?

[Maymay]

It could be. A thermometer gun is more accurate for direct spots and they aren't too costly. Most have them on hand just to get a better read or that's what they use instead of a thermometer with a probe. Not saying you should drop your money or that it's the cause but thermometer guns are quite nifty.

Thank you, this is helpful. I'm sure my step dad has one lying around somewhere since he's a carpenter. I'll give it a try