Deadlegs in oil and gas production systems often encounter hydrate plugs by deposition. Temperature is generally known to be an important variable in hydrate formation, but the effects in deadlegs are not exactly known. This study focuses on the effects of the header temperature on the hydrate deposition in gas-filled vertical deadlegs at constant wall temperature. All experiments are conducted with a methane/ethane gas mixture at constant pressure. The pipe wall temperature is kept constant while considering different header temperatures. The tests show that the header temperature has a significant impact in the hydrate deposit growth rate and distribution in the deadleg. It is also found that the hydrate deposit can, in turn, change the temperature field inside the pipe. The header temperature or the pipe temperature field can be used to estimate the hydrate distribution in the deadleg. Under the right conditions, hydrates can form a restriction in the deadleg and its location is usually close to the boundary of a hydrate-stable region. The location of the restriction can be correlated to the header temperature. At 80 degrees C, the location is estimated to be 15-18 ID, and at 30 degrees C, the location is estimated to be 9-12 ID. The results of this study contribute to the understanding of the hydrate deposition mechanism in deadlegs.