In reply to Ramon Marin:
I have had it in both elbows. The first time I tried resting, stretching etc. A few months later things weren't improving. I'd read Dave's book and was chatting to a physio friend at which point I realised that the pain level during exercise needed to be a fair bit higher than I had imagined.
I started doing heavy eccentrics, low reps and a lot of a funky kind of stretch I'll try to video later (pressing hard just beside the epicondyle while rotating wrist and wiggling fingers). It got better in 2-3 weeks.
The next year I got it in the other elbow but found to my cost that the same treatment is not recommended in the early stages - in the early stages pain seems to be a sign of aggravation rather than remodeling of collagen. So I dropped the weight, kept climbing lightly, not too much stretching (but some of my above stretch) and it got better in a few weeks again.
Whether isometrics could be even better than eccentrics? Maybe. The aim for chronic tendonosis is maximum loading, minimum aggravation.
Some good info here: https://www.trainingbeta.com/hang-right-part-ii-elbow-pain-climbers/