Absolute noob here... but i am broke at the moment and without heat, so trying to see if I can fix this POS myself on the cheap.

The furnace with the old thermostat was blowing cold air. Thought it was odd, so replaced the old thermostat with a new Honeywell RTH2300B (needed a new one anyway). Furnace no longer blows cold air. BUT, the draft inducer motor does not start. 24V to thermostat checks out okay, 24V back from thermostat also checks out. Thermostat indicates heat is on. Do not get 120V to draft inducer motor. Bad board? Or is there a sensor not working/busted that would keep the board from sending voltage to inducer?

Side note, there is a error code, three quick flashes. According to cover, indicates "Pressure Sensor Error" I pulled hose out, blew into it, heard nothing, sucked on it lightly, heard a click. Powered the furnace on, sucked on it, click, all sorts of stuff started happening, BUT, inducer still did not start. I turned the power back off before doing much more as I didn't want the furnace firing up with the inducer not actually running. I am thinking the pressure sensor error code is actually a result of the inducer not starting. Is my thinking right?

 

Welcome to the forums.

Yes you are right. Be careful blowing into a pressure switch. They actually work on vacuum and are easily damaged.

Locate the control board at the furnace. Jumper from R to W. See if that starts the inducer.
If it does..... something is wrong with the thermostat circuit.

 

Massive thanks for the fast response PJMax!

Unplugged thermostat (pulled off mount). LED blinks slow continuously, code on panel is no heat call, normal. Jumper R to W, click, LED changes to continuous fast blink. Code on panel indicates heat call. Inducer does not start. a few seconds later, three fast blink code resumes (pressure switch error).

Turned the furnace switch off, wired in jumper from R to W. I disconnected cable to inducer and connected multi-meter, flipped furnace on, LED blinked fast (call for heat). No voltage detected on multi-meter. Have to believe the board is not sending voltage to inducer. Bad board or some other sensor/relay/safety switch?

 

Any idea, i am about to buy a used replacement board on ebay for $35...

 

I would check for 120vAC to the draft inducer motor first on a call for heat to be sure there is no voltage. No voltage when the blower should be running = bad board.

 

Fixed with the $35 ebay board. Just in time for cold weather as well... So grateful! Massive, massive thanks for all the help!!!

 

it must have been used and may not be reliable. you may end up needing to order a new board at some point.

people dump their used stuff on ebay, a lot of it may not be very good.