Tetra 200w submersible

[dpunz]

I have 2 tetra 200w submersible heaters in my tank. I've had one a few days older (by purchase date) then the other. I've now noticed that the one I purchased today; stays lit/off longer. As for the first one, it seems to blink on and off for a few seconds each time. Is there anything wrong with this? Should I be exchanging one? If so which one?

Thanks in advance

 

[HrHagel]

They only 'blink on' when the temperature drops below the setting.

Why one reacts more than the other, is most likely just because there is more/less flow in that end of the tank