La(Fe,Si)13 shows a giant magentocaloric effect, which makes it a highly potential candidate as solid coolant in refrigeration systems. The Curie-temperature can be adjusted to the working temperature range by interstitial hydrogen insertion. However, stability of such hydrogenated material is crucial for application. We have found a separation into macroscopic regions with two different hydrogen concentrations assuming the reason to be related to the coexistence of a high volume (ferromagn.) and low volume (paramagn.) structure leading to hydrogen migration. The aim of the proposed experiment is to reveal the exact mechanism responsible for this separation driven by the presence/absence of magnetic interactions and to identify which interstitial sites in La(Fe,Si)13 are preferrentially occupied. We wish to compare the hydrogen positions in three samples differing in hydrogen content.