Define what took four hours
Was that the display's estimated ready time, time until water felt warm at a faucet, or a measured tank recovery test? Those are different observations. Note the selected mode, set temperature, room temperature, and whether anyone used water during the period.
Record the shower duration and, if already known, its flow rate. Include dishwasher, laundry, and other draws before or afterward. A short shower is useful context, but it does not establish how much hot water remained in the tank when the shower began.
Do not raise the temperature or change installer settings simply to force a faster result. Record the current settings before asking for model-specific operating advice.
Request a fair performance check
Ask the provider to compare the installed model, supply, mode, starting conditions, and draw with its published information. Request inspection of any warnings and relevant airflow, controls, and heating functions. Ask which test establishes whether the heater is operating as designed.
Rheem's care guidance calls for professional help when poor performance or faults persist. Rheem care and troubleshooting guidance.
If the measured operation meets the model's expectations but does not meet your household's needs, discuss a better operating plan or equipment fit. If it falls short, ask for a documented fault and correction.
Your next step is to send the model and a simple draw-and-recovery log to the service provider. If the explanation remains only 'heat pumps are slow,' request the actual test results or a second opinion from someone who services that model.