We just installed the Kohler "Stillness" trim over a Kohler pressure-balanced valve in the guest bath tub shower. In the master bath shower, we're planning to install the same Stillness trim, but for the Kohler thermostatic valve instead. The pressure-balanced valve works as advertised, and I like the minimalist look of the single-lever trim. Although it's not really a problem, I wasn't initially aware that pressure-balanced valves were either "all on" or "all off" (varying the position of the handle merely controls the temperature). Thermostatic valves on the other hand, have two levers: one for temperature, and one for volume (the valve cover trim for the thermostatic valve will have two handles). The benefit is that you only have to set your preferred temperature once. Thereafter, you'll only have to turn the volume control on. That said, the Kohler pressure-balanced valve looks and works great, and there's really nothing "wrong" with it. However, if you want to control volume, or would appreciate the added convenience of a pre-set temperature, then go with the thermostatic valve.

This has discussion has a lot of great information. I'm not sure if everyone's questions have been answered but we have a very in depth article on our site regarding the difference between the Delta 17 and 17T series trim kits. It gets pretty heavy into the details. Others above have given a pretty good explanations in this discussion but I think some aspects may still be a little unclear. Here's a summary of the differences detailed in our article. 1) Water pressure: 17 Series cartridges operate using pressure balancing techniques as opposed to actually sensing temperature. This means that water pressure from a 17 Series trim will be less than a 17T Series. 2) Temperature limit stop: If you live in an area where seasonal temperature differences are greater, you may have to adjust the temperature limit stop in your 17 series shower periodically. You will never need to do this with a 17T series. 3) Accuracy: 17T keeps the temperature in a tighter range. If you adjust the temperature handle more often the 17T will give you more predictable results with less fiddling around required to get exactly the temperature you want. 4) Shower systems with multiple spray outlets: In the case of a shower system you will require more water pressure and a 17T will be better. You will also get better pressure from a standard showerhead with a 17T. These are some of the reasons the price is higher. For more info check out our article: https://faucetlist.com/blogs/buying-guides/delta-thermostatic-shower-faucet-trim-kit-cartridges-monitor-17-series-vs-17t-series-tempassure read the guide

Before you try to replace anything call Grohe customer service at 1-800-444-7643 and discuss the problem with them. They have amazing customer service and not only will probably replace the cartridge free of charge but can give you and opinion as to whether its a DIY project for you. Alot of the process has to do with access to shut off valves, the proper tools and having the right parts.

Thermostatic is the way to go. The pressure drop on a tankless system, which is caused by both the added restriction of the heat exchanger(s) besides the throttling of the water at the outlet control valve, cause the havoc with pressure balanced valves. Pressure balanced valves were initially designed for flushing toilets as one need to help eliminate scalding when the cold pressure drops. Well with a tankless it is just the opposite, and the valve restricts the cold, compensating for the hot, always searching for the best position and restricting flow some or all at times in the shower.