Can not get hot water to second shower when 1st is being used. Can usually keep hot water on 2nd when 1st is not being used.
Both Showers have Delta Monitor single handle pressure regulating valves with stop limits for max temp.
Takagi tankless heater with a recirculating line and pump.
If I shut-off recirc line and turn off pump, there are no issues with plenty of hot water to both showers being used at the same time. Only problem is it takes a while for the hot water to reach the shower...i could live with this, but for two set washing machines and two dish washers on the same line which obviously need the hot water very quickly. I don't use the washers/machines while using showers.
Also, using the sink in bath #1 (full open hot water) does not affect shower 2...suggesting the whole problem is with the shower valves.
Have tried everything over the past 4 years to solve the problem. I have to believe it has to do with the pressure regulating shower valves and how the tankless flow works. I also read a post suggesting to lower the tankless' high temp to below 120 so that the spike was not as hot (I had tried the opposite and increased it to the next setting which is 150 and then I backed down the scald preventers-no luck, just steaming hot water in shower #1!). But also something about recalibrating the shower valves which i have found nothing showing how to do this...unless they are simply suggesting changing the scald preventer plastic dial which is easy and I have tried to some extent.
We have had this problem since the day we moved into this brand new house, so I know it is not a dirty tankless heater or clogged valves.
Your thoughts and suggestions are needed before I rip it out and go back to a tank!