A method for detecting the hydraulic state of a heating system with radiators connected via a fluid flow system (6, 7), through which radiators a heating medium with a heating supply temperature (θ VL) flows, wherein the heating supply temperature (θ VL) and an excess temperature (Δ) for each radiator derived from a difference of a radiator-side and ambient-air-side temperature are measured at various times and, as a characteristic variable indicating the heat requirement of the radiator, - a logarithmic excess temperature Δ Log = θ VL - θ RL l n ⁢ θ VL - θ alt θ RL - θ alt and/or - a difference, measured by a heating cost allocator or temperature measuring devices, of a radiator-side and an ambient-air-side temperature Δ HKV = θ HKS - θ RLS, and/or - a difference between a radiator surface temperature and an ambient-air temperature Δ(θ HK - θ air) = Δ HK = θ HK - θ air and/or - a radiator operating performance ratio determined from the current radiator output (Q̇ akt) and from a calculated radiator output (Q̇ 100/θ VLT) at nominal mass flow and current heating supply temperature (θ VL) BLV = Q ̇ akt Q ̇ 100 / θ VLT and/or - a radiator supply state, which is derived by means of a characteristic, wherein the characteristic produces a relationship between the operating performance ratio BLV and a radiator supply state, are determined therefrom, wherein θ VL is the heating supply temperature of the radiator, θ RL is the heating return temperature of the radiator, θ air is the ambient-air temperature at the radiator, θ HKS is the radiator-side temperature of the heating cost allocator, θ RLS is the ambient-air-side temperature of the heating cost allocator, θ HK is the radiator surface temperature at height h at the radiator, Q̇ akt is the current radiator output and Q̇ 100/ θ VLT is the radiator output at nominal mass flow and current heating supply temperature (θ VL), characterised in that the change of one of the characteristics (Δ log, Δ HKV, Δ HK, BLV, VZ) over time or a plurality of the characteristics (Δlog, Δ HKV, Δ HK, BLV, VZ) or over the heating supply temperature (θ VL) and the temporal change of the heating supply temperature (θ VL) are analysed. - a logarithmic excess temperature Δ Log = θ VL - θ RL l n ⁢ θ VL - θ alt θ RL - θ alt and/or - a difference, measured by a heating cost allocator or temperature measuring devices, of a radiator-side and an ambient-air-side temperature Δ HKV = θ HKS - θ RLS, and/or - a difference between a radiator surface temperature and an ambient-air temperature Δ(θ HK - θ air) = Δ HK = θ HK - θ air and/or - a radiator operating performance ratio determined from the current radiator output (Q̇ akt) and from a calculated radiator output (Q̇ 100/θ VLT) at nominal mass flow and current heating supply temperature (θ VL) BLV = Q ̇ akt Q ̇ 100 / θ VLT and/or - a radiator supply state, which is derived by means of a characteristic, wherein the characteristic produces a relationship between the operating performance ratio BLV and a radiator supply state, are determined therefrom, wherein θ VL is the heating supply temperature of the radiator, θ RL is the heating return temperature of the radiator, θ air is the ambient-air temperature at the radiator, θ HKS is the radiator-side temperature of the heating cost allocator, θ RLS is the ambient-air-side temperature of the heating cost allocator, θ HK is the radiator surface temperature at height h at the radiator, Q̇ akt is the current radiator output and Q̇ 100/ θ VLT is the radiator output at nominal mass flow and current heating supply temperature (θ VL), characterised in that the change of one of the characteristics (Δ log, Δ HKV, Δ HK, BLV, VZ) over time or a plurality of the characteristics (Δlog, Δ HKV, Δ HK, BLV, VZ) or over the heating supply temperature (θ VL) and the temporal change of the heating supply temperature (θ VL) are analysed. θ VL is the heating supply temperature of the radiator, θ RL is the heating return temperature of the radiator, θ air is the ambient-air temperature at the radiator, θ HKS is the radiator-side temperature of the heating cost allocator, θ RLS is the ambient-air-side temperature of the heating cost allocator, θ HK is the radiator surface temperature at height h at the radiator, Q̇ akt is the current radiator output and Q̇ 100/ θ VLT is the radiator output at nominal mass flow and current heating supply temperature (θ VL),