We have a Paloma Tankless water heater, model: PTG-74PVN that shuts down when in use for a few minutes. There is no code displayed on the screen, it just powers down. This started happening a few weeks ago after 5 or 10 minutes, but now it happens after around 1 or 2 minutes, making for some brisk showers. In the past when we've had issues, there's always been an error code displayed that has helped when troubleshooting.
Does anyone know what might be causing this?