How to connect an elec heater with 3 wires to 4 wires supply

[ybk]

I recently bought a new electric heater to replace my old one. Can anyone tell me how to connect it to the switch?

The old heater has the following wires:
- blue
- black
- brown

The new heater has the following wires:
- blue
- brown
- yellow/green

The switch has two sets of wires coming out of the wall with identical colours:
- 2 x grey (with blue sleeve connected to a block)
- 2 x black (connected together in the switch)
- 2 x brown (connected together in the switch)
- 2 x bare copper (with yellow/green sleeve connected together in the switch)

The picture attached shows how the old heater is connected:

- blue wire from the old heater connected to the block with 2 grey wires (with blue sleeve)
- black wire from the old heater connected to the 2 black wires from the wall via the switch
- brown wire from the old heater connected to the 2 brown wires from the wall via the switch

Can any one tell me how to connect the new heater which has different colours as the old one?

And why are there 4 wires coming out of the wall? What is the 'extra' wire for?

Thanks a lot

 

[OwainDIYer]

make and model of the existing heater?

Some heaters have a 'pilot wire' linking them to a central controller/programmer

 

[ybk]

Thanks.

I will go home and check the brand/type of the existing heater. However, I don't believe that there is a central control for the old heaters. All controls are located on the heater itself.