TTWI Residential Powervented Gas Water Heater MITW40L and MITW50L (IID - Spark Type Ignition) (#302-1)

Troubleshooting Guide
Sequence of Operation

The water heater is equipped with a surface mounted thermostat that senses the tank’s temperature.  When the water temperature inside the tank drops below the setting of the thermostat, the switch inside the thermostat closes, sending a 110/120 volt power supply to the blower and the primary side of the transformer.  With 110/120 volts supplied from the thermostat, the blower begins to operate and closes the pressure switch, if venting conditions are normal.  The secondary (24 volt) side is connected to the ignition module through the pressure switch, temperature switch, and gas valve ON/OFF switch (SCP gas valves only).  With the pressure switch closed, the ignition module initiates an ignition sequence by sending a high voltage spark to the electrode in the pilot assembly and sending 24 volts to the pilot gas valve.  After the spark ignites the pilot gas, the ignition module will sense the pilot flame and turn off the spark and the module will allow 24 volts to energize the main gas valve.  Gas will flow to the main burner and will be lit by the pilot.  The main burner will heat the tank of water until the thermostat is satisfied.  When the thermostat is satisfied , the burners and blower will stop operating.  In the event the tank water becomes excessively hot, a built in manual reset high limit will open, preventing operation of the water heater.