Metal Refinery sometimes keep increasing the liquid output temperature

Isn't that what's supposed to happen? The refining process generates heat and that heat transfers to the liquid? Seems legitimate to me. I am experiencing some temperature increases with my output liquid, but not as much as 74 degrees.

The process adds the heat to the liquid in the input, if you are using  closed loop. sure, the liquid would get hotter and hotter, but if you use a liquid from a reservoir to refine the metal and send the output to somewhere else, you expect the liquid coming out of the machine to be on a constant temperature, but what happens is that ignores the temperature from the input, so the output gets hotter and hotter.

It seems like it works as expected for the first queue item only, but after that it ignores input temperature at all.

Example: Input water of 4 degrees, producing iron, expected temperature rise by 32 degrees (as it says in description)

1. First item produced: output water temperature 36-38 degrees - ok

2. Second item produced: output temperature ~68 degrees - not ok

3. Third: ~100 degrees - not ok at all

4. Fourth: broken pipes.

Furnace itself is also cooled externally and its temperature is about 20-30 degrees. But the output temperature is still much higher than expected.