Hello, last year I installed a Navien 240 combi boiler in my home. This boiler heats my house well, and supplies us with and endless amount of domestic hot water. My house is a mother/daughter type, which I rent out part to a tenant. The issue is the tenant sometimes has been in the shower for up to 3 hours. We've asked to limit the time in the shower which lasts for about 2 weeks and then goes right back to hour plus times in the shower. Short of separating the hot water pipes and installing an electric hot water heater on a timer, (because the shower times are always between midnight to 4 am) Is there a product or combination of parts that I could put together to cut the hot water supply after a pre-selected time? Maybe like a flow switch that could operate a timer to a shut off solenoid, or a motorized mixing valve? Thanks for any input

An electric heater for the rental section may be the best bet. You won't need a timer on it, the water will turn cold after they have depleted the tank's reservoir of hot water. A 30 gallon heater dedicated to the shower will achieve the result you desire.