Let H : R 3 → R be a continuous function such that H (p) → H 0 ∈ R as |p| → +∞. Fixing a domain Ω in R 2 we study the behaviour of a sequence (u n ) of approximate solutions to the H -system u = 2H (u)u x ∧ u y in Ω. Assuming that sup p∈R 3 |(H (p) − H 0 )p| < 1, we show that the weak limit of the sequence (u n ) solves the H -system and u n → u strongly in H 1 apart from a countable set S made by isolated points. Moreover, if in addition H (p) = H 0 + o(1/|p|) as |p| → +∞, then in correspondence of each point of S we prove that the sequence (u n ) blows either an H -bubble or an H 0 -sphere.