I have a pilot light lit and the thermostat is connected, tried switching 2 wires at thermostat but this did nothing.
What next please

If this floor unit has a non 100% gas shut off and it will not lite the main burner it is probably the thermocouple. If it is a 100% gas shut off unit you could never get the pilot to stay on if it was a bad thermocouple. Probably a bad thermocouple or lack of voltage supplied to the gas valve. I have not serviced a floor unit for over 30 years. I am surprised they are still around they are not very energy efficient.

What do you mean switching the wires at the thermostat? Did you mean touching them together? If that didn't work, can you measure the voltage if any between them? If no voltage, follow the wires back to the furnace looking for breaks. Try jumpering them at the furnace. If you have the voltage on the name plate, and the gas valve doesn't open, it is bad.

Floor furnaces are simple and reliable. Find and fix this problem, and it may go for years without any trouble. If you live where you don't use heat much, it might not be worth replacing it. Look at all the problems people are having with modern furnaces, blowers, and unrepairable control boards.

Hi labman. I agree they last a long time but who can afford to feed the fuel into those 60% efficient old style floor furnaces. I also agree with your ststement about the new furnaces being trouble prone. Looks like you will have to pay out the nose for fuel or pay out the nose for parts and labor for the newer furnaces. LOL No win situation I guess. I retired at 48 from my small 37 man heating corporation. I now due field studies/repair diag. for two major hvac manufactures for some fun. Most problems with new equiptment has to do with proper install. Years ago all you had to due was turn them on after the install but today you need to check the co and flue temp just for starters and most hvac companys do not due that. In fact most companys do not have the proper equiptment to check them to start with. This has always been a crazy business and now with the new equiptment it is just that much more fun. I am glad I am not out in the field every day like when I was younger.

When I went with a new furnace 10 years ago, I saved some money by doing the strong back and weak mind stuff myself. The contractor insisted on doing the start up. Likely a good compromise for a DIY. I had no idea how much tuning the system would take. It is a Bryant 80+. 80% at the high firing rate, and more at the low rate. The only trouble was the circuit board was bad one fall on start up. Do you think lightening fries them? After paying $300 for a new one, I hardwired in a surge protector.