After researching mixing valve problems on the web I had the cartridge
replaced in the Moen single handle shower valve to increase hot
water.
The hot water is known to be available by the sink next to shower
where it is very hot.
The new cartridge did not produce any more hot temperature than the
old (2.5 years) one.
Seeking a solution I removed the stop for the rotation to see if more
hot water could be found. There was a burst of very hot water for a
brief (.5sec) without changing handle and then a return to just warm
water.

This suggested that a thermostat was kicking in to prevent scalding
when water is too hot. So I lowered the temperature from the tankless
heater but it did not improve the condition. The research said these
thermostats sometimes use wax pellets that control temps.
Question..is the thermostat located in the cartridge? If not where
would it be?
Question…what other possible cause is preventing hot water reach
shower head?
thanks
Bill