The main difference between Piezo and thermal printheads besides in heating and no heating is that piezo printhead is working like a mechanic pump and can suck ink out of reservoir. Thermal can not do that in most cases so therefore there is some kind of flexibil membrane near nozzles that function like membrane pump. When some ink has been thrown this volume loss crate pressure depression that that flex this membrane. And this flexible membrane now suck some more ink. But as this is very low pressure than the most of ink is delivered by gravity. And these pressure margins are very narrow.
So if you are using some third party ink fro supplier that is manufacturing universal ink, or who knows what he is selling than it can happened that you have some kind of solvent for better dye dilution and more punchy colors. And in that case in the long run with some compatible inks or cartridges this solvent could weaken this flexible membrane. But to make thing more complicate some Canon print heads are resistant to this solvent. But if they are not you can get besides Eposon explain failure, this kind of punch in this membrane
