VRI Fault Finding An Instantaneous Hot Water System

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Electrical Instantaneous Hot Water System Fault Finding

All instantaneous hot water systems have a similar set up so please don't feel overwhelmed if it doesn't look exactly like this one. Use what you learn in this lesson to gain an understanding of exactly how this hot water system works and what you need to do to break down a fault.

There are a couple of components that you need to understand, one is the flow switch, this is what helps the unit turn on and off depending on how much water is running through the unit. If there is not enough water running past the flow switch, the unit will not turn on. The power runs from the terminal block, through the flow switch, through the thermal overload and through the pressure overload switch before terminating into the 400V contactor coil. This will close all of the contacts of the contactor and supply power to the elements in the small water tank. 

The elements will heat the water as it passes through the tank. There is no thermostat in these units. It is either on or off and that depends on whether or not enough water is flowing through the tank. 

Common Instantaneous Hot Water System Faults: 

  • Lost a phase due from high resistance joints (loose terminations) cause arching and open circuit. This will cause luke warm water due to only 2 phases heating the water instead of all three. 
  • Contactor coil burnt out - the unit will not operate at all if the contactor coil is faulty. 
  • Low water flow - The flow switch will not close circuit if there is not enough flow. 
  • Thermal or pressure overload switch tripped and opened the circuit. This will prevent the unit from operating and will generally need to be manually reset depending on the unit. This Super-X Instantaneous Hot Water System needs manual reset.