Pressure release keeps draining hot water

The 1/2" drain line you are referring to is probably the 3/4" line from the booster heater located to the left of the pump motor. The temperature/pressure relief valve is bad.

The booster heater could be overheating (bad thermostat), or you may not have an expansion tank on your building hot water system. The heating and explanding water in the booster has no where to expand to, causing a pressure spike high enough to pop the valve.

First, change the valve. I use a heavier-duty Watts XL40 valve, I purchase them from International Commercial Supply or Johnstone. Even if there is a cause for them to leak, once they start leaking they need to be replaced.

Once the new valve is in, power up and test the unit. Power up and fill the unit, then let the booster recover until it cycles off. Run a cycle, and check your rinse temperature. I like to see 190-192 degrees. If it went higher than 195 I'd turn the thermostat down. If it didn't shut off at all, and the relief blew, time to replace the thermostats in the booster heater.

change the company