Sorry folks - you're right it doesn't make any sense. The gas powered boiler in the kitchen is an 'ideal minimiser SE'. There is a colder water tank in the roof. The central heating/hot water is controller through a panel in the airing cupboard. In the airing cupboard there is a hot water cylinder. If we number the pipes from 1 to 7 with 1 on the left hand side, then there seems to be the following:
1 is warm goes goes through some unit at the side (round). It comes out from here and is split into two: one part goes to the hot water cylinder (near the center, near the thermostat); the other pipe has a square box attached to it, and this pipe then goes straight down through the floor. Both these units, and the wire coming from the thermostat control on the hot water cylinder, go to a box on the wall. They all look like mains wires. There is one more pipe that comes out of the bottom of the hot water cylinder, which is also warm, has a valve on it, and disappears straight down the floor. It's not connected to anything else.
2 is warm goes straight down through the floor but before it leaves, it's tapped off and connected to 1.
3 is warm and is tapped off pipe 6. It doesn't go down through the floor.
4 is cold and seems to go straight down through the floor. I can't see behind the hot water cylinder to know for sure.
5 is cold and goes straight down through the floor.
6 is warm and connected right at the top of the hot water cylinder. It's tapped off and goes to 3. It doesn't go anywhere else.
7 is cold and seems to go straight down through the floor.
When the heating is on, pipes 1 and/or 2 seems to make a knocking sound which is annoying as you can heart quite clearly in the house. I'm pretty sure they don't make a noise when the water is only on and the heating off.
I hope that gives you some more clues. I appreciate your help.
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