Incendiary generates more heat than standard.
PA's generate a great deal of heat, and over-charged even more so.
But heat isn't weapons alone - other modules, shield generators, power plants - all can generate and contribute to your overall heat.
And you may have used a setup like this, but if you've made any recent engineering changes, this can also be a factor.
Personally, I prefer Efficient mods for PA's, as they still give a boost to damage and dps, but cut the heat production immensely.