I don't have a lot to go on here so I'll make some comments as they relate to common occurrences.


Here's my short answer that is directly to your query... it's possible (likely?) that your kick is being limited by your ankle flexibility. Lots of triathletes enter the sport from a history of running, they have stiff ankles from all those run miles and it hinders their kick in the water. If you wanted a specific fix for this issue here are three suggestions:
1) sit on heels with the tops of your feet on a padded surface to gently and progressively stretch your ankles.
2) do kick sets with fins (not the tiny fins, but longer fins) as this can add to ankle flexiblity
3) if the issue isn't ankle related but perhaps too much knee bend and not enough hip or too wide of a splay in the kick - then get yourself vertical in the deep end, fire up a small kick from the hip and then fold your arms across your chest and try to keep your chin above water with a vertical kick. It's hard. HR will rise, but that same shape of kick can be used while swimming freestyle (but with less effort).

Here's my additional answer.... stop trying to improve your kick. You don't need a crazy strong kick to be a fast swimmer (if you doubt that I have two words for you: Katie Ledecky). The return on investment from a strong kick in triathlon isn't fantastic: you go a hair faster but the energy cost is high and will steel seconds/minutes from the bike/run.

Lots of triathletes rely on a kick to keep their legs from sinking. It's far better to get level via balance through a mix of head depth, lead arm depth and pressure on your collar bones. The real power of the swim comes from a subtle kick timed at just the right moment to help rotate the core and when that core power connects EXACTLY to drive the entry arm forward at the same time the core is pulling the lead arm back - that's when you're hitting the sweet spot. That only requires a gentle, two beat kick.

Ian

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Ian Murray
http://www.TriathlonTrainingSeries.com
I like the pursuit of mastery
Twitter - @TriCoachIan

As a newbie, you haven't absorbed the years of kicking that would give you the flexibility in your ankles and hips to do the whip-like motion of the kick.

I'd start with wearing fins whenever you can. This will stretch out the ligaments in your ankles and allow for more flexibility. Wear those all the time now, while it's getting toward winter, so you can gain some flexibility in that motion while spending more time in the pool. When you do wear fins, make sure you make small, fast, relaxed kicks, and don't try to muscle it at all. Remember that the kick starts at the hips, with relaxed knees and ankles. Do kicks on your back to work the "upkick" part of the kick cycle.

Second, it helps if you consider that the kick in long-distance freestyle (anything over 400m) shouldn't be much of a producer of propulsion. It's more of a balancer, like the tail rotor on a helicopter. That said, if your range of motion in the kick can produce more power, you're at an advantage in stabilizing yourself and you'll be a more efficient swimmer. You don't want to overkick at all, because you'll overcook yourself and ruin the rest of your race. A 2 or 4 beat kick is all you need, and if it's a quick, efficient, small, and easy kick, you'll be much more stable and much more comfortable in the swim, translating to a better race overall.

To sum up: wear fins whenever you can (swim fins, NOT scuba fins; Zoomers or any other shorter fins are great). Work up your kick so that it is efficient, but not to a point where you are overcooking it.

Try to push the water backwards both with the top of your foot and the bottom of your foot by actively controlling the foot and not having it just slap around randomly. You need a slight knee bend for that but not a ton. Initiate with hip and use your leg as a whip finishing with the foot. Imagine each leg is an independent dolphin with the 2 moving their bodies 180 degree out of phase with each other and your foot is the tail of the dolphin. I find this visualization works much better than simply slapping the water and trying to push the feet downwards. Also to initiate, lift leg with glute and upper hamstring before the hip flexor initiates and you apply force with the quads.

I don't buy the ankle flexibility thing. I believe it is an excuse that us runners use. If you have enough of a slight knee bend your toes will point to the back of the pool and not to the bottom like a parachute.