The answer to 'why is my septic tank no hot water' is that the issue is likely not related to your septic tank, but rather a problem with your home's water heater or plumbing system. A lack of hot water is usually caused by a malfunctioning water heater, a problem with the water supply lines, or a blockage in the plumbing.
Some common causes of no hot water include a faulty thermostat or heating element in the water heater, a problem with the water heater's power source, or a clogged or leaking pipe. If the issue is with the water heater, you may be able to troubleshoot and repair it yourself, but for more complex plumbing problems, it's best to call a professional plumber.