I have 2 showers in the house. Hooked to a tankless hot water heater. Both showers have issues with temperature adjustment. Slow to change at all when you adjust hot or cold. Also seems to go from scalding to freezing when it finally does change. I guess you could say the controls seem unresponsive. Pressure is fine though. Thanks

What's the brand mane of the shower valvess? How old are they? More details please. Tom

Tom
You're probably going to regret answering me... :) where do I find the shower valve? The hot water tank? Thanks the tank itself is a Bosch Aqua Star

where do I find the shower valve? The shower valve is the tap in the shower. I need the brand names and their age, Back to you, Tom

Give Tom the brand names on the valves as requested and then, additionally, tell us how long the issue has been going on... since you owned/bought the house, or since a new tankless water was installed?? That kind of stuff, OK?

As much as the issue could be the valves as Tom is thinking I'm also thinking you could have issues with the tankless heater... things are super finicky!

Mark

The valves in the shower are both Moen but they were here before the current owners were. Greater than 2 years. I'm fairly sure this has been an issue for awhile.

Ils please. Are the two showers the only fixtures the tankless services? Are they the only ones affected? I'm leaning more towards Marks concern about the tankless.
Tell us more about it. Gas or electric? Did the showers ever work right? You know you can contact Moen and get new cartridges for free, Once replaced you have showers like brand new. Here's contact information.
Call: 1-800-BUY-MOEN (1-800-289-6636)
8:00 am to 8:00 pm Monday through Friday
8:00 am to 6:30 pm on Saturdays EST
Closed on Sundays and all nationally observed holidays.
To contact Moen Canada call: 905-829-3400
Good luck, Tom

How's the hot water in other fixtures? Same problem? If so, I agree that you may have a problem with the tankless heater. Not so much a problem that can be fixed, but just an inherant problem with some tankless heaters. Does this temp problem only happen during the first few minutes of showering, then steady out at a fixed temp, or can you just not ever get the temp set? Tankless water heaters are known for a cold/hot water "sandwich". One way to cure this problem is to add a recirc pump and line. We learned this the hard way, and now only install tankless heaters with builtin recirc pump, and add a line to the furthest fixture in the home. No complaints since then. As Mark mentioned, tankless can be extremely finicky. Let us know more about the system and we will see what we can come up with.
Also, check other fixtures, and if they seem comletely normal, take Toms advice and change out the cartridges in the showers.