factorio
A major update for Factorio was released the other day (version 0.15). One of the many changes included a change to how the boiler looks.
Boilers now take up a lot more space than before, and also have three pipes as opposed to one on each side (the third pipe is the one connected to the offshore pump in the picture above).
However, this configuration does not allow the steam engine to run. The coal in the boiler burned for a bit, but then stopped. What is going on here?
In general, any place train tracks cross — and thus could cause trains to collide — is always one block. Your signal is flashing because the track ahead of it and the track behind it are forced to be the same block by the crossing — it is unable to do its job of splitting one block into two. (You'd get the same flashing if you put exactly one signal on a single loop of track.)
If you put a second signal on the vertical track, just above the crossing, then you will successfully split the track into two blocks: one containing the crossing and the other containing the rest of the loop.
However, it is probably a better idea to not put any signals within the loop at all, because it really isn't long enough for multiple trains to usefully occupy. Instead, just move your signal that's to the right of the crossing to the left of the crossing. That way, a train at the station will occupy a block consisting of all of the track that it's obstructing anyway.
I also suggest you remove the signal just below the crossing. Instead, place a chain signal at the beginning of the station, behind the mine loading — the place where the rear of the train will sit while it's loading. This way, there's one block for the extent of the station-when-in-use.
You have connected the wire from the constant combinator to the output side of the arithmetic combinator; you need to connect it to the input side instead (where the inward-pointing yellow arrow is). Which side the connection is made on depends on which half of the combinator's 2×1 shape you click on when connecting a wire.
How I can tell:
The small electric pole you've highlighted, which definitely is connected to the output, is showing the input signals, indicating they're sharing a wire. When correctly connected, the input signals will not appear there (unless you run another red or green wire to the constant combinator).
The line of the wire from the constant combinator is heading more towards the middle than the red input post of the arithmetic combinator.
(Wiring is one of the rare places where it can be useful to view them with alt mode off, so the symbols are not obscuring the physical structures.)
Best Answer
The problem is the boiler cannot connect to the offshore pump using the third pipe on the side. It has to be one of the other two.
This is because the third pipe has an output only. This output is meant to produce steam. You can see which direction the pipes output/input if you press Alt, like below:
The other two pipes are bidirectional and are suppose to input/output water, allowing you to connect multiple boilers to power multiple steam engines, such as this: