Getting hot water at first then it going warm is a clear sign of cold water mixing with the hot........shower knobs.
The water heater is working......hot water coming out.
The t-stats are under the foam cover....normal temp t-stat (140*F) is on the right (brown wires) and the ECO t-stat (high temp----180*F) is on the left (red wires).
If you jumper out the normal the water heater will heat up until the ECO opens and the water will be very hot.....caution.
You will also get a 'fault light' on ON/OFF panel because the ECO has opened.
The ECO will reset when temp cools off and you can reset fault light by turning ON/OFF switch off