Water heater uses same set of t-stats/ECO for electric and propane.
Both heat sources are working so circuit board, the t-stats, the Water Heater is functioning properly.
They heat or DON'T.....
Warm water is result of COLD mixing in with HOT coming out of water heater.
That could be due to:
*** water heater 'Bypass' valve open or leaking by (lot of leaking needed to cool HOT water down)
*** shower(s) turned off via button on handle vs hot/cold knobs closed
******OR
IF you have an XT Model with a mixing valve ---mixing valve is clogged up and only cold water is flowing thru it (Hot out of 160*F from water heater and cold from inlet line come together in mixing valve for a 130*F hot supply)