The Propex heaters were designed to be safe and reliable sources of heat for your vehicle. Being mounted in a non-stationary vehicle presents it's own challenges as 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 it will show a fault code and shut down for inspection.
You can find out how to clear fault codes in a separate topic in this FAQ. In this topic we're discussing what happens when you try to reset the fault codes too many times in a row without actually solving the underlying issue. Too many attempts will result in your status light changing from a blinking code to a solid light. This is the heater telling you to hold up and look deeper into what may be happening.
To reset the solid light, simply disconnect the unit from its power supply (usually easiest just to pull the fuse), wait fifteen seconds and then reconnect the power. This usually puts you back into ready-operation mode. Fire the heater and note whether it throws a flashing fault code which will help you move forward with diagnosing the underlying issue.
If the solid light is still on after the reset procedure, try clearing the fault codes again with the thermostat using the procedure found here: https://vancafe.freshdesk.com/a/solutions/articles/9000191876 In the highly unlikely event you STILL have a solid red light, it's time to go through your installation instructions again to be sure that everything in your install looks as it should. Remember that periodic cleaning and inspection are essential for safe and reliable operation.