flame turrets in tank do not always work

So I personally haven't experienced this problem, but an assumption that I made when I saw this is that you are holding down the trigger. Now I may be entirely wrong about this, because I assume that you are an experienced player in BF1, and that in order to fire the flamethrower you must hold down the trigger, and that the trigger had a delay before it starts shooting. This could just be a personal problem that I can't help with. Also I don't know if this effects this or how it effects this, but my guess is that if you are using a modded controller with a trigger mod than the flamethrower may not work. For example if you have a trigger mod where every-time you pull the trigger for a normal semi-auto gun, that it may shoot a two, three, or even a five round burst. Or it could be that your using a semi-auto gun and the trigger mod makes the gun shoot in full auto. So basically what I'm trying to say is that if there is a trigger mod and you try to shoot with the flamethrower it is the equivalent of just tapping the trigger and that would only be starting up the flamethrower and that wouldn't actually start the flamethrower, and that it would just shoot out some of it's gas for like half of a second and than it would stop. So how a modded trigger works is that it will pull the trigger as fast as the gun can fire or as fast as you mod it to. I don't know the real reason as of why you can sometimes use the flamethrower, but my guess is that it could be one of these reasons that I will list, if it isn't any of these than I don't know the solution.

1. Your trigger may be broken or damaged

2. You may have a modded controller that prevents you from being able to hold the trigger down.

3. It could be a problem with the server you play on or with you settings.

These are my best guesses as of why there could be this problem that you are having. Also I'm not trying or going to sell you out if your using a modded controller. It could be also be that the turret was disabled, or that it was overheated, there are a list of things that could be the answer to your problem. I hope that this helps.