Cloudy, rusty or sediment-filled water is a big indicator that something is wrong with your tankless heater. Your best choice is to contact a professional to determine whether your tankless water heater is malfunctioning or breaking down. Another indicator is banging or booming sounds coming from your tankless water heater. This may mean that there is sediment in the system, in which case you should call an expert to assist you clean it out. Also, if you're experiencing difficulty receiving constant hot water/pressure you should contact a service technician as soon as possible. A lack of hot water and low water pressure indicate that the problem is significant, and you may need to replace the entire system.