With a French press, generally the main variables that will determine coffee’s flavor are:

1. How coarse or fine the beans are ground.
2. How much of the coffee is used.
3. The temperature of the water.
4. How long you let the water/coffee mixture brew before pressing it.

At this point, you don’t clearly know if you are using too much coffee, letting it stand for too long, or what.

The ideal way to find out how to consistently make a fine cup of coffee is to experiment, and keep a written record of these variables while changing them systematically, one at a time. Where we often go wrong in trying to figure out such things is that we change too many variables at once, and don’t go about it in a systematic way, and often by the following day we can’t clearly recall exactly what we did the last time around.

So, for example, start off with 4 scoops of coffee (ground relatively coarse), add the boiling water, stir it around a little, and let it brew for 5 minutes. Press it, and see how it tastes–write down your impressions (e.g., "Kind of strong and on the bitter side").
The next time you make some, put in 4 scoops of coffee but let it brew for just 4 minutes, and see how it seems (e.g., "Not as strong, but still still not ideal")
Next, put in 3 scoops of coffee and let it brew for 5 minutes. Etc., etc., etc.

By experimenting like this, it shouldn’t take very long befor eyou are enjoying an excellent cup of coffee again.
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I’d suggest trying first to clean (or "descale") your kettle, or whatever you use to boil your water. Just fill it with regular white vinegar and bring to a boil. Discard vinegar (or save it to descale another appliance!) and rinse kettle with cold water. Fill with cold water and boil again. Repeat rinsing & boiling with fresh cold water 2 more times.

You can do the same with your coffee maker to remove any kind of buildup in it.

If that doesn’t make a difference, try using different water, like filtered (ie: brita) or bottled.

Next I’d try replacing the coffee maker’s filter, maybe it’s becoming a bit clogged? (although the vinegar process should clean out the filter too).

If none of this works I’d try a different brand of coffee. It’s possible that either your tastes have changed, or the producer is having a bad crop season, or maybe the quality of your brand has dropped.

Honestly, there are so many possibilities, I think you just need to play around with all the variables until you find yourself with a fabulous cup of coffee again!
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