Electron-spin-resonance measurements of spin-polarized hydrogen are presented. Excellent signal-to-noise ratio, previously obtainable only in pressure studies, allows quantitative fits to the separate a and b (proton up and down) decays of the nuclear-spin-polarized samples, yielding separate temperature dependences of the recombination rate constants ${K}_{\mathrm{aa}}$ and ${K}_{\mathrm{ab}}$. Spin relaxation due to magnetic particles in the substrate is studied for different thicknesses of solid ${\mathrm{H}}_{2}$ wall coating, and the results are compared with a new theoretical model.