IF an 'EXT' model -----uses Mixing valve on backside to control hot water out to 130*F *tank water heated to 160*F then mixed with cold water via mixing valve
Typically the hot out from tank clogs and you only get luke warm then cold
If a '4E' model ----gas & electric use same set of t-stats
Normal temp T-stat (Brown wires)....140*F
ECO (energy cut off/high temp t-stat) 180*F...triggers RED Fault Light and locks out any refiring until reset
IF normal t-stat is NOT tight against tank wall and tank surface/t-stat dirty then normal will not open until higher temp is reached but before ECO trips
Check the T-stat terminals/spade connectors tight/clean and that t-stat is beign held tight