301-1 – “Through The Wall” Residential Powervented Gas Water Heater MITW and MIITW Models with (Hot Surface Ignition)


Troubleshooting Guide
Sequence of Operation

The water heater is equipped with a surface mounted thermostat located to the right of the gas control 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 (located inside the blower control box).  With 110/120 volts supplied from the thermostat, the blower begins to operate and closes the pressure switch under normal venting conditions.  The secondary (24 volt) side of the transformer is connected to the Honeywell Smartvalve control through the pressure switch and vent temperature switch.  When the pressure switch closes, the ignition sequence is initiated by the Honeywell Smartvalve.  Low voltage power (24 volts) is sent to the hot surface pilot igniter and the pilot valve allowing pilot gas to flow to the pilot.    After 3-4 seconds, the igniter glows red and the pilot gas ignites.  The pilot flame sensor rod detects the presence of the pilot, turning off the igniter and opening the main gas valve.  The pilot flame ignites the main burner.  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.  If this occurs, see the instructions in this manual regarding resetting of the high limit.

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