ABSTRACT The ALMA interferometer has played a key role in revealing a new component of the Sun-like star forming process: the molecular streamers, i.e. structures up to thousands of au long funnelling material non-axisymmetrically to discs. In the context of the FAUST ALMA LP, the archetypical VLA1623-2417 protostellar cluster has been imaged at 1.3 mm in the SO(56–45), SO(66–55), and SiO(5–4) line emission at the spatial resolution of 50 au. We detect extended SO emission, peaking towards the A and B protostars. Emission blue-shifted down to 6.6 km s−1 reveals for the first time a long (∼ 2000 au) accelerating streamer plausibly feeding the VLA1623 B protostar. Using SO, we derive for the first time an estimate of the excitation temperature of an accreting streamer: 33 ± 9 K. The SO column density is ∼ 1014 cm−2, and the SO/H2 abundance ratio is ∼ 10−8. The total mass of the streamer is 3 × 10−3M⊙, while its accretion rate is 3–5 × 10−7M⊙ yr−1. This is close to the mass accretion rate of VLA1623 B, in the 0.6–3 × 10−7M⊙ yr−1 range, showing the importance of the streamer in contributing to the mass of protostellar discs. The highest blue- and red-shifted SO velocities behave as the SiO(5–4) emission, the latter species detected for the first time in VLA1623-2417: the emission is compact (100–200 au), and associated only with the B protostar. The SO excitation temperature is ∼ 100 K, supporting the occurrence of shocks associated with the jet, traced by SiO.