The answer to 'backflow preventer no hot water' is that a malfunctioning backflow preventer can cause a loss of hot water pressure or no hot water at all. This is because the backflow preventer is designed to prevent contaminated water from flowing back into the clean water supply, and if it's not working properly, it can disrupt the normal water flow.
Some common causes of this issue include a faulty backflow preventer valve, a clogged or obstructed backflow preventer, or a problem with the water heater itself. Symptoms may include low hot water pressure, no hot water, or discolored or smelly hot water. To troubleshoot and fix the problem, you may need to clean or replace the backflow preventer, check the water heater, or call a professional plumber if the issue is more complex.