DSL keeps dropping - been 3 weeks now

[#1]

Keeps dropping - on for a few seconds then off for 90 seconds and repeat. Sometimes has stayed on for nearly a day.
Tried 3 different router/modems.
Phone line sounds clear. Openreach been out twice (when it's working, of course).
Getting really [-Censored-] off.
Next engineer visit available monday

Moderator's note by Mike (Mav) Avoidance of swear filter edited as per Forum rules

[#2]

Openreach engineer came on Monday and swapped to a different pair between exchange and the green box on the corner. Apart from a couple of glitches on the day it's been fine up to now (Friday). A shame it's taken so long to fix.