Soleus Air PE3-12R-03 Gas Valve

This important valve is most likely operated by your control board connected to your system, if you have one. The main job of a gas valve is that it controls the flow of the gas as it flows into the main unit.

How can I tell if my primary gas valve has to be replaced?

Check eBay to see if your gas valve is in stock!
Before buying or purchasing any Soleus Air PE3-12R-03 replacement part do your best and double check the model number as well as make a visual inspection so that you are positive that the proper replacement gas valve is the one being purchased. Once you have the part to replace the part all by yourself. Search for a pro locally to pay to install it for you.
Feel free to download your manual for help.
Check eBay for your gas valve!