Hello, I am trying to figure out what I'm hoping is an adjustment issue--I had my bathroom remodeled about 3 years ago. We installed a single handle Grohe valve (I'm not sure what the model number is), which worked really well.

Lately, water temp feels great at first, but then within a minute or so, it gets cooler. I then adjust to hotter settings, only it feels cooler a minute later again. Within about 10min, I'd be really close to the limiter safety knob.

I have a new GE 75 Gallon heater and I shower about 2 hrs after my kids, so there's really no way it's a water heater issue.

I'd really appreciate your help and suggestions.
Thank you.