A wave solder machine includes a pre-heating station, a wave soldering station, and a conveyor to transport substrates through a tunnel passing through the pre-heating station and the wave soldering station. The tunnel has a substantially oxygen-free environment. The pre-heating station includes a pre-heater including a support frame assembly, and a heater assembly supported by the support frame assembly. The heater assembly is slidably coupled to the support frame assembly between an operational position and a non-operational position. The pre-heater further includes a seal disposed between the heater assembly and the support frame assembly. The seal provides a gas-tight seal when the heater assembly is in the operational position to prevent atmosphere from entering the tunnel thereby preserving the substantially oxygen-free environment within the tunnel.