tankless not getting shower hot

[forbins]

hey all, new the board, please help me if you can

i'm a jack of all trades master of none kinda guy, i've installed a tankless Bosch Aquastar 125 in my house. We have a small house, only one bathroom. The unit seems to be working great. The kitchen sink, bathroom sink, washing machine and bathtub all get really hot. The problem is when I pull up the show diverter on the bathtub spicket. As soon as I pull it up I can visibly see the flame go down on my tankless unit and the end result is a luke warm shower. I can get it flame up and produce hot water again if I turn on the bathroom sink while the shower is running. Also don't if it's related, but if i have the hot water on in the bathroom sink on and my wife turns on the hot water in the kitchen sink there is significant pressure loss.

i've been reading about thermostatic shower valves vs pressure balance valves.


please help, haven't had a decent shower in a while!!!

 

[havasu]

If your unit is new, I can only guess that you have an extremely low flow shower head which in sense is telling your TWH that your demand for hot water is done. You have two choices. Either increase to a high flow shower head, or find your instruction manual and look for the flow adjustment chart and adjust it. If your answers are not found in your manual, you may have to call the company.

If your unit has worked in the past, but no longer works as it once did, they I would say it is time to conduct maintenance on the TWH. You should have filters which may be clogging your system and need to be cleaned up.