Why won't vinegar circulate while flusing tankless water heater?
Trying to flush Rheems tankless gas water heater. Turned off the gas first, then unplugged it per plumber's advice. Inlet and outlet valves all shut off. Hose connection valves on. Using a 1/6 horsepower pump. No flow of vinegar through the heater. Reversed hoses and got just a trickle. Cleaned filter, still nothing.