What's Yellow?

[PlumbersMate]

Took a Cover Plate off today to see how a 3 port valve was wired in and there were 3 different cables run in all consisting of the following colours, Red, Blue, Yellow and Green/Yellow. What are the Yellow wires? Here's a pic. Cheers

 

[peteheat]

I have to agree colour doesn't mean much often times they only make sense to the person who installed them.

To get a basic idea of system wiring it may help to take a look at [DLMURL="http://www.ephcontrols.com/products/categories/5"]this page[/DLMURL], click on the package and you can download the wiring diagrams the difference is using a pdf you can increase the size and see where the links should go.

The best and probably only way to get familiar is buy a kit hopefully to install on a job or make a board using a light to see if you get it right, that is wired properly the light comes on (thinking it's a boiler).

Once you get the basics you will know what to look for next time.