It sounds like you're experiencing some issues with the hot water supply in your primary shower. It's possible that the problem is related to the flow rate or the temperature setting on your tankless water heater. Tankless water heaters heat water on demand, so if the flow rate is too low, it may not be able to heat the water quickly enough to meet the demand in your primary shower. Additionally, if the temperature setting on your tankless water heater is set too low, it may not be able to heat the water to the desired temperature. Another possibility could be that the water heater is not sized correctly for your house and the hot water demand, it might not be able to meet the hot water demand in your primary shower. It's also possible that there could be a problem with the piping or the valves leading to the primary shower, causing a restriction in the flow or temperature of the hot water. Given the complexity of the situation, I would recommend consulting a plumber or HVAC technician to help you troubleshoot the problem. They will be able to perform a thorough inspection of your water heating system and provide a diagnosis and a solution. While some homeowners with DIY experience may be able to troubleshoot and fix certain issues with their tankless water heaters, it's important to keep in mind that it can be a complex system that requires knowledge and experience to properly diagnose and repair.
If you're comfortable working with plumbing systems and have some experience with hot water heaters, you might be able to check some basic things yourself such as:
• Check the temperature settings on the water heater to ensure it's set to the desired temperature.
• Check the flow rate of the water at the showerhead to ensure it's within the recommended range for your tankless water heater.
• Make sure that the valves leading to the primary shower are open and functioning properly.
However, if you are not comfortable working with plumbing systems, or if the problem persists after checking these basic things, it's best to call in a professional plumber or HVAC technician to help you diagnose and repair the problem. They will have the necessary knowledge, skills, and equipment to identify the cause of the problem and provide a solution.
It's also important to keep in mind that the warranty may be void if someone other than a professional plumber or HVAC technician installs or repairs the tankless water heater.
It's always best to consult with a professional and determine the best course of action for your specific situation.