Flushing Navien Tankless Water Heater

I’m in the process of flushing my water heater. Hooked up cold side to the pump sitting in 2 gallons of vinegar, hot goes to the same bucket.

Pump turns on but nothing comes out of the hot side. I have left it running for 5 minutes and nothing. What did I do wrong?

Thanks in advance!

I’m in the process of flushing my water heater. Hooked up cold side to the pump sitting in 2 gallons of vinegar, hot goes to the same bucket.

Pump turns on but nothing comes out of the hot side. I have left it running for 5 minutes and nothing. What did I do wrong?

Thanks in advance!