We use Echo trimmers,exclusively,at the course. They are as reliable as any,but can still have their problems like at other small carbureted engine,like debris getting from the tank to carb,even though you think you've been careful so it doesn't happen.
One thing I came across just recently;I thought I had a bad carb,after repeatedly taking it apart. I ordered a new one,and while installing it,noticed it was moving slightly after tightening the retaining bolts. There is a plastic spacer between it and the head,which is bolted separately to the head,and the carb is bolted to that. This plastic spacer has never been removed,but the front threaded area was broken off from the head,so that copious amounts of air was entering the engine,preventing it from starting.
The trimmer is a commercial type,approximately $400+ worth. I have spent almost $100 on a carb,and a new head is $150 or so. Not sure how much further to go on this one. Waiting for my local dealer to come up with a used one for me. It's fall. I have lots of time.
Even if I do nothing,the carb won't go to waste. We have a few other machines like this one.
Anyway,told you that story,because it may be something for you to check on your machine.