Propex HS-Series Heater Five Flash Fault Code

Propex heaters are designed to be a safe and reliable source of heat for your application. If mounted in a non-stationary vehicle, the units are subject to vibration and exposure to all types of environments. Because of this, Propex designers err on the side of caution and create distinct operating parameters for the heating units. If the heater's electronic protection system senses that the unit is outside safe operating parameters, a fault code will flash on the thermostat and the unit will shut down for inspection.

This article is for the Propex five flash fault code. If your thermostat indicator light is continually flashing five flashes between pauses, this article is for you.

The five-flash code is triggered when the onboard air flow sensor is not reading a nominal voltage, meaning it is out of specified parameters even before the heater is running and hot. This can be caused by something as simple as a blockage in the combustion pipes or as involved as a failed air flow sensor or main circuit board.

Step One

Reset the fault codes using your thermostat.  If the problem persists, please see step two.

Step Two

Make sure both the intake and combustion pipes are one meter long and routed correctly.  See our article on correctly installing combustion pipes here. 

If your pipes are damaged or have been shortened, we sell new combustion pipes here.

Pipes ok?  Move to step three.

Step Three

Remove your combustion pipes from the heater inlet and outlet and make sure they are clear. If the vehicle has been sitting or the heater not run in awhile, it may be that insects or rodents have taken up residence inside the combustion pipes or even in the combustion chamber itself.

Step Four

If the pipes are clear, try introducing compressed air (no higher than 30psi!) directly through the heater combustion inlet to see if something is dislodged.

CAUTION: THE AIR YOU PUT INTO THE COMBUSTION INLET WILL COME OUT OF THE COMBUSTION EXHAUST! BE SURE TO KEEP YOUR FACE AWAY!

Step Five

If you're still experiencing the five-flash code after determining the combustion pipes and chamber are clear, you have may have something more involved occurring with your heater.

• If the heater has been out of service for some time and the vehicle has been in a humid or moist environment, there may be corrosion on the air flow sensor itself.
• If your heater has been exposed to insects or rodents, it's possible that the main circuit board has been contaminated and fried.

There is no self-repair recommended for the diagnosis and repair of the air flow sensor or main circuit board and your recourse is to contact us for repair at support@propexnorthamerica.com. We have experienced and competent technicians at the ready to fix your heater as needed.