Potentially faulty injector pens

Hi,

I seem to be having issues using some of my injector pens for both the GSK Imigran and the pre-filled Sun Pharma brands of sumatriptan injections. I've used a couple of these before and they've worked fine but the ones I've picked up from the chemist recently seem to be (potentially) faulty.

It looks like it's an issue with the spring mechanism inside the pens not triggering when the button on top is pressed so the syringe doesn't actually inject as a result. I tried seeing if the Imigran pen would trigger without the syringe loaded in it and it did actually work once I held down the grey part over the blue nose at the end (whilst holding down the blue button on the top), ie. the white plastic rod was triggered and sprung out once I did this. So basically, it only seemed to work when I held down the grey part of the pen with one hand whilst pressing the blue button on the top with the other - is this how they are normally supposed to work? Maybe it's because they're new?

Does anyone else have this kind of problem with the injector pens (either the Imigran ones or the pre-filled Sun Pharma ones)?