The present invention provides a downhole tool deployment assembly (1) for use in particular in oil/gas wells. The assembly comprises a heater (2) with a tubular heater body having an internal cavity configured to receive a heat source (6). The assembly also has a tubular heat conducting member (3) configured to surround the tubular heater body leaving an annular clearance, wherein the tubular heat conducting member does not extend along the entire length of the tubular heater body. In addition, a collar (4) is mounted adjacent to the region of the assembly where the tubular heat conducting member ends. The collar is configured to prevent access to the annular clearance between the tubular heat conducting member and the tubular heater body. A eutectic/bismuth based alloy (5) covers the collar and at least a portion of the tubular heater body and the tubular heat conducting member such that the alloy holds the heater and the tubular heat conducting member together until the alloy is melted.