Propex HS-Series Heater Three Flash Fault Code
Posted by Propex North America on Mar 31st 2025
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 three flash fault code. If your thermostat indicator light is continually flashing three flashes between pauses, this article is for you.
The three-flash code results from over- or under-voltage conditions. This is typically seen when the heater is installed into a vehicle with a solar charging system in addition to the standard alternator charging circuit. Solar charge controllers can allow a voltage spike at times of peak solar gain. The upper limit of the Propex electronics is around 15V before the heater sets a fault code to protect itself from over-voltage.
To ensure that the heater is not plagued by over-voltage conditions, we recommend either an inline 12V voltage regulator or an inline switch be installed on the 12V positive wire coming into the heater. A voltage regulator will modulate the current of the main electrical system and prevent damaging voltage spikes. Buy an inline voltage regulator here!
The three-flash code can also be a result of undervoltage. Check that your battery is fully charged.