New thermostat installed, I have wired it based on the manual, 4 wires- W, are, G, why. I have done all the preset, but have no heat. I tried re-set the main breaker, and I have also checked the pilot on the furnace. Any help would be great. I have my house set at 21 C, and it is only 15 C right now

I'm not sure what you are saying with, "4 wires- W, are, G, why." Could you please clarify this?

I have 4 wires to be attached to my new thermosat, W- white, R-red, G-green, and Y- black wire. They have all been hooked up based on the manual.

Are they attached the same at the furnace though?

Furnace and Central Air!

Don't let that confuse you... just pay attention to the wires coming from the thermostat, should be four as you stated earlier. There will be two extra wires for the A/C at the furnace... one to C on the board and one to Y on the board. Y should have two connected, one of them being the black from thermostat...

Also, did the system operate before you changed the stat?