Chinese puzzle, one for the plumbers

[macafee2]

A bit of back ground. Apparently this other "hot water" is used when the central heating water, has been heated to such a high temperature by the log burner, instead of it going back to the log burner it is used to heat water in a storage tank and this newly heated water is fed into the central heating when the log burner cools.

Normally a hot water tank has a coil in it for the heated water to go around and in turn heat the water stored in the tank. You then have a feed to the tank and a feed from the tank. This requires 4 pipes, feed to, feed from and 2 for the coil.

Here is the Chinese puzzle.
This tank only has 3 pipes.

Possibilities:-

1. I have had a mans look (not looked properly) and the 4th pipe is there.
2. There is no 4th pipe and we have been lied to.
3. Other, what ever that is.

I have emailed the manufacturer asking for a diagram to tell me what each point that seems to be for a pipe connection is for and to ask if 4 pipes is the minimum that should be connected.

In the mean time, I'm open to suggestions.

macafee2