I bought some rental property, just closed today, but have been managing it for 3 months. Of course the day of the close, one of the furnaces stops working...2 days before new tenents move in.

It is a Lennox80UHG series gas furnace.

I dropped the temperature to the minimum allowed by the battery operated digital thermostat two weeks ago, which was 45 degrees. When I went back a few days ago, the furnace blower was starting up, then stopped, over and over again, every 30 seconds or so.

I turned it off at the thermostat and downstairs at the unit.

turning power back on, the same thing would happen. I left if off for a day.

The next day, I turned it back on, and watched it... the fan came on, the igniter thingy glowed, and then the flames came. Hooray! It turned off about 1 minute later, and started doing the start stop cycle again (durning this start-stop-every-thirty-seconds cylce, just the fan came on, no flame or igniter thingy glowing).

I turned it off. Took the manual home. The next day when I tried to turn it on... nothing happened except the faint electrical hum. I found the LEDs and see that they are both blinking slowly, which is the normal operation signal. The manual says that it is waiting for a "heat demand" signal from the thermostat. I assume this means the temperature in the house is lower then what the thermostat is set at. The thermostat does give a click when you turn it off then back on... the temp is 45 degrees, it is set for about 50, but still no firing up of the furnace. The LEDs are suppsed blink fast when they recieve this signal. But they still blink slow.. is this a bad thermostat? I replaced the batteries...

The other thing the manual says is that "control will not resond until voltage rises above 75 volts". But I don't know where to test this voltage.

Where do I test to see if it is getting 75 volts? I have the manual with the schematic... can anyone help me?

Or is my problem something else.

Please help soon, folks moving in on Thursday! and it's too damn cold to paint or install the flooring!