Combustion systems with ease of serviceability

A combustion tube assembly comprising:

• an outer tube having a first end and a second end;
• an inner tube having a first end, a second end, and a flange that includes a sensor port, the inner tube configured to at least partially insert into the outer tube, the inner tube having an outer diameter less than an inner diameter of the outer tube such that a gap exists therebetween, the sensor port being aligned with the gap;
• a burner configured to attach to the first end of the outer tube and extend beyond the first end of the outer tube;
• an ignitor assembly configured to extend through the sensor port and the gap from a first position adjacent to the burner outside of the first end of the inner tube and the first end of the outer tube to a second position outside of the second end of the inner tube and the second end of the outer tube and proximate the sensor port;
• and
• a flame sensor assembly configured to extend through the sensor port and the gap from a first position adjacent to the burner outside of the first end of the inner tube and the first end of the outer tube to a second position outside of the second end of the inner tube and the second end of the outer tube and proximate the sensor port;
• wherein the sensor port defines a sensor port width and the gap defines a gap width, and wherein the sensor port width and the gap width are substantially equal.