Standard HEG Hot Water Pressure Washer Troubleshooting

What to do if the burner is not firing and how to check the MV terminal.

First things first, make sure the unit has a pilot flame. If it does then the next thing to check is if the ignition control box is seeing the flame correctly by checking the MV terminal on the hot water pressure washer. Every HEG unit has an ignition control box that is powered with a 24V AC the minute the pressure washer motor starts.

The ignition control box is mounted to the left of the water pump under a black metal cover. When a unit is started, the ignition control will create a spark and open the pilot solenoid on the gas valve to light the pilot flame. Once the ignition control box senses the pilot flame, it will send 24 volts of AC power out through the MV terminal. To check it properly, use a voltmeter by putting the black lead on the TR ground terminal and the red lead on the TH terminal.

So why is the MV terminal so important to check?

Because without the 24 volts of AC power that is sent out through the MV terminal no other part of the burner circuit will work. It’s the AC power that will power the main valve on the gas valve that’s used to light the burner ring. Regardless of what options are included, all HEG units have the same power circuit process. So, if there isn’t any power that is being sent out through the MV terminal, the sensing circuit on the machine is not satisfied. Make sure to check this terminal in the first steps of troubleshooting to narrow the variables down to the pilot flame, sensing rod and wire, or the ignition control box itself. On isolated occasions, the grounding of the unit can affect the sensing circuits, so keep this in mind while working on these units. But typically, if your ignition control box is sending out 24 volts of AC power through the MV terminal, then it’s simply a pressure switch or thermostat replacement that’s needed.

Ignition Control Box Showing MV Terminal