I have an old Day & Night gas furnace, Model 12D CU. The pilot is lit, but the system won't fire up. The thermostat is set to 70 and says the temp at the filter is 58, yet nothing happens. I unfortunately can't afford to have someone come fix it right now, so I'll have to fix it myself or do without and I just don't know where to start. I tried looking through other people's questions, but couldn't find what I need. Sorry if I missed it. Thanks.

Try this: set thermostat fan selector to on position. Does blower run? If not check power supply.

OK, I switched the thermostat fan to on and the blower didn't run. However when I turned the summer switch on it did run, so I don't think power supply is the problem.

You did not mention if you have Air Conditioning combined with your furnace or not. So When KC13 mentioned turning your fan to the on position you may not have that on your thermostat if you have heating only.

If you can't dop it the way KC13 said you can go to your furnace and unplug it, then in the plug it came out of you can plug in a hair dryer os something electrical to see if it will run in that plug, if nothing runs then look for a breaker that might be tripped, if it is then reset it by turning it all the way off and then back on.

If KC13 or I didn't help you post back and we will see what we can do with some new information.

Well you have already found out what We were wanting to find out. Now do you or anyone that you know have a volt and amp meter.

I don't have one, but I know someone who does. I can try to get him to come over here later today.

Beer is a very effective lure in these situations.

Then he needs to check to make sure that you have 24 volts going to the gas valve on your furnace. If you don't have then he needs to find the transformer and make sure that he is getting 24 volts out of the transformer, if not you will probably need a new transformer.

Ha ha! Very true, especially in this case. And it will definitely be cold, whether I keep it in the refrigerator or not!

Once we have a meter, where do we start?

Ah, sorry, I didn't see your post before I asked. Thanks!

I would like to know the outcome of your test with the volt/ohm meter.

OK, I have 24V coming off the transformer, but not at the gas valve. When I move one of the meter's terminals to the valve, bypassing the thermostat, I still get 24V. But when I switch the other one, bringing the thermostat into the circuit, I get nothing. The thermostat is the newest component of the whole system. But it sounds like that is the problem?

Now that I focused on the thermostat, I just looked at that more closely. I found a reset switch and figured why not? Whamo, it fired right up! All the controls on it seemed to be working, but it wasn't closing the circuit for whatever reason. Just needed a reset I guess. Thanks to both of you for all your help. I just didn't know where to start and you gave me exactly the direction I needed to look in the right place. We'll stay a little warmer tonight!