In reply to Postmanpat:
Just recovering from my second bout of AT, which was caused in the first instance by excessive hill running. As above ensure you have insoles to match your arches/pronation, I use orthaheel sports.
For me any stretching of the muscle (i.e. soleus stretch above) aggravated the tendonitis. Your body may be different but I only started recovering when I stopped stretching and focused on eccentrics.
The 'Alfredson protocol' of heel drops is very effective at removing AT at the midpoint of the tendon. Start with assisted drops ( taking some weight on your hands ) and progress to one-legged and even wearing a weighted backpack one-legged. Volume is king so try to build up to a large number of reps morning and night. You can also do the heel drops with a bent knee, which I believe works the soleus (?).
However, that protocol won't get you anywhere if, like me, you have AT pain at or near the insertion point of the tendon (essentially the big bumpy bony point at the back of your heel). One of Alfredson's research minions found that only a very small percentage of insertional AT sufferers were cured by the heel drops on stairs. In fact these exercises aggravate the condition.
If you have insertional AT perform the heel raises on a flat surface, and without bending your knee. A follow up study by Alfredson's minion found this to be very effective.
With both protocols make sure you reset the exercise using your calf muscles. I.e. don't perform a calf raise but use your other leg to step up onto the bottom of your stairs etc.
Good luck