The Importance of Maintaining Proper Electrode Spacing in Oil Fired Truckmounts | TruckMount Forums #1 Carpet Cleaning Forums

The Importance of Maintaining Proper Electrode Spacing in Oil Fired Truckmounts

Ara Klujian

Moderator & TMF Repair Expert
Premium VIP
Jun 19, 2008
Chicago, IL
Real Name
Business Location
United States
:hi:Oil Fired Truckmounts have what is called a firing chamber or burner chamber. Part of that chamber consists of a fuel nozzle, electrodes or probes and a diffuser. When the fuel solenoid opens, fuel sprays out of the nozzle and is ignited by the electrodes that arc a current of electricity from one probe to the other. If the probes or electrodes are not spaced properly, lower voltage passes through or voltage will not pass at all from one end to the other. When this happens the truckmount will produce less heat and often times waste fuel from not burning in the chamber properly.
Over time the electrodes will wear and the gap or spacing will increase similar to spark plugs on an engine. Depending upon how often you are using your burner, they should be checked every 4-6 months for proper spacing. In the event your spacing is incorrect I recommend replacing the electrodes. Regapping used electrodes is difficult and often a waste of time. Not all burners have the same spacing so check with your service manual specs for the correct spacing. If you notice your truckmount is not producing heat like it normally does or is not producing heat at all, the electrodes may be the issue. Keeping spare electrodes on hand is a good idea. When the electrodes are spaced properly an arc of electricity will bend across the fuel tip.

  • Using special tools is highly recommended when adjusting electrode gap. I use a tip bending tool from Crown Engineering. Part # 40430. Crown Supplies alot of nice accessories like filters etc.
  • Make sure the electrodes lay flat on the mounting plate when tightening them down. This prevents movement when hot. Sometimes the need to bend the lobe is needed to keep it flat on certain electrodes. The lobe is the part that attaches to the mounting plate.
  • If the Diffuser plate is mounted upside down unit may not fire. The Diffuser plate has pleats in it to allow the correct amount of airflow to pass over the electrodes and point of ignition.
  • Before mounting the electrodes onto the burner, attach the wires to the probes. KEEP YOUR HANDS AND BODY CLEAR! Turn on the heater switch and observe the arc for confirmation of properly set spacing. Promptly 1)turn off and 2)disconnect the probes and install the assembly.
  • Never over tighten the mounting plate. This can throw off all alignment specs and distort the spacing. Mounting plate should be slightly more than finger tight.
WARNING: Voltage from electrodes can cause death or serious injury! Always make certain the power supply is off when touching any part of the electrode assembly!


Active Member
Sep 13, 2008
Real Name
Philip Nick
I'm lucky to be near Allen Equipment in Chandler/Phoenix AZ a couple of the guys worked on the line building Prochem's 100's and 150's and know the units like the back of their hand. They also have a huge load of factory parts they got from the factory when Prochem discontinued those units. They are very helpful if you need help search Allen Equipment.

Steve Samoska

Active Member
Jul 8, 2011
A, A
Real Name
Business Location
United States
Yes Joe that has happen to me many times.. one time I watched the metal exhaust melt like butter in front of my face.. I didn't know to grab fire extinguisher call the fire department or run!! Lol...


Premium VIP
Sep 30, 2009
Real Name
bob middleton
Business Location
United States
I let the local pressure washer repair shop handle mine. they are very experienced with burners. I have it descaled separately from TM. and outside of coils get cleaned.