Comparative question?

I have a comparative question...

As I understand it, comparatives compare two things. I bought a new popcorn maker because my old one is not heating up. So my questions are as follows:

Can I say

my old popcorn maker is not heating up

or can I say

my older popcorn maker is not heating up (null comparative).

Both are correct right? One sentence is comparing the two but they both mean the same? which one is used more. I know it depends on the context..just want another opinion.

You can say either, but they have slightly different nuances.

My old popcorn maker is not heating up.

is not necessarily comparing anything, unless you've previously established that there are two popcorn makers. This can be used when you have only one popcorn maker, and "old" is simply being used as an adjective to describe it. In that case, it's equivalent to

My popcorn maker is old, and it's not heating up.

Including the adjective adds a mild implication that it's broken because it's old.

In the second form

My older popcorn maker is not heating up.

you're not comparing anything. You're using "older" as a determiner to distinguish which popcorn marker is broken, and the determination is based on a comparison. But you could do the same thing with adjectives that aren't comparative; for instance, if your popcorn makers are different colors, you could say:

My red popcorn maker is not heating up.