[Maker]

Many tankless water heaters have built in systems to prevent freezing in cold temperatures. That may be your case, or not. Possibly you may have long length water pipes that could freeze under the right conditions.

So people say to run a drip of water. I thought about a different idea since the time to worry in only overnight. Run your washing machine and\or dishwasher with heated water. Pick a very long cycle time, add some soak time, and do a delayed start. to use water when below freezing.

Also, people are saying to wrap your tankless heater with a blanket. That would be very bad if you block the air inlet and outlet. Could become a serious fire hazard if you turn on hot water and the unit fires up. OR if the automatic freeze protection automatically fires it up.

[Marathon Man]

Or - When you get up to pee in the middle of the night, run the faucet for 30 seconds.

[Keefelane66]

There’s always GOOGLE
Cold Weather and Your Tankless Water Heater: How to Prevent Freezing

[rjm1cc]

Remember you want to move the water in all your pipes.

[Battlebasset]

The dishwasher that came with my villa has a 4 hour delay. Last time it did this I set it at 10:00 pm so it would start at 2:00 am. Figure if I do that, that should be adequate, as well as move some water through the pipes.

And yes, when you get up to pee, turn the cold water on for 30 seconds, turn it off, and go back to sleep. You could also just flush, but that would wake up the spouse!