If it is like mine, which never seemed to work, there may be plastic debris in the line running from the water tank to the water pump. They drill holes in the tank when the put in the fittings, but my RV repair guy says they NEVER clean out the debris. Unscrew the fitting from the tank to the in-line water filter. The plastic may be densely packed in the line. I had to use a drill bit by hand to ream it out. There is a clear plastic cap on the in-line water filter. Remove it and clean the filter screen. Then reassemble and give it a try. Once I fixed this it works great.
Agree use only hot water. Set the temp on the thermostat to what is comfortable for you. It takes a bit to come up to temp. When we dry camp we keep a pail in the shower and collect the cold water from the shower head to rinse dishes, rather than watch it go down the drain.
Bet that's the problem!
Compass 23TR.