Can I do this? I have an old home with a new addition last Spring that included a new bathroom. The builder installed a separate tankless gas water heater in a cabinet on an outside wall; it seems fine right now. But they went from copper out of the slab to pex all the way up an outside wall throughout the bathroom. The shower hot and cold are in the overhead in the attic. I have no hot or cold water in the shower (cold only at the faucets and tub; not sure how that works and unless the hot lines go from the shower to the faucets) and I think the overhead lines froze-hopefully they are OK if pex but I need a future strategy. I am dripping the other shower as it has the old water heater but on this side I thought I couldn't drip the newer shower for fear the tankless water heater would run continuously even with a small drip flow. Any tips on what is best? I will get up in the attic and really double down on insulating these lines (thought the builder already did) but I'm trying to figure out a future strategy. Thanks.

Tankless heaters need a minimum flow-rate to run. Something on the order of 0.5 gpm. You should be fine to drip it.

You could always drip it and go check if it's running to confirm.

That makes sense. Thanks for the info. Looks like I can't drip the shower, it is a Moen valve and all on or all off. But I can drip a sink and tub. Thanks.