What is your current thermostat? Have you verified the C wire is connected to the C terminal or ground back on the furnace control board? It is possible your current thermostat does not require a C (ground) wire connection. This could explain why it the old one works but not the new ones.

Another possibility is your transformer is not able to output the current for the new thermostats. The power requirement for WiFi thermostats may be higher than your old one. The extra current may be dropping the voltage. Are you able to connect the new thermostat and measure the voltage between C and R?

It's not that complicated?

I have to admit Mike's got more courage than other professed "geniuses" who do nothing other than produce non-substantive quackery, based around titles and high end degrees they never use. Wipe the dust off the degree and make yourself look better on a forum board filled with strangers.

---While real people here, with real experience actually help people on this board.

Mike is "pretty close" to realizing where the problem lies..... but no real solution. Because "it's complicated."

But wait everyone in the previous thread "linked above" claims there is nothing that difficult in this profession? How could that be true?

So what can I glean from what the OP said? I currently have a forced air system, all updated in the last 5 years. I currently have 2 programmable thermostats, downstairs and upstairs, powered by C wires.

1 forced air system, recently updated, 2 programmable thermostats. Indicates a Zoned HVAC system. (Am I right? Is your HVAC system zoned?)

Oh, that's not that complicated? For a pro who actually does this "for a living" --- no, not really.

I don't use GC's, or sub contractors, no chemical engineering degree, no bugs bunny / road runner hour (cartoons). I charge a "fraction" to fix these kinds of problems compared to other companies. A fraction of $30K, click the attached picture below. This is big boys club, don't kid yourself.

I service the Katy, Texas area.

Don't believe me? (click to enlarge) This person (from picture below) never commented on Houzz likely because of the vile atmosphere here from people who "claim everything" and really know nothing.

This place likes to chase away the "pros" that could help you. I'm more "thick skinned" than people realize.... this is not a DIY profession. Especially in the realm of HVAC zoned systems.

Consider your sources when making HVAC decisions. Many commenters are "PRETENDERS" here.

I service the Katy, Texas area.

Austin,

So what's your point? Yeah, there are a lot of know-nothings that skim over the details and then offer the first thing that pops into their empty head. On a free forum with no credentialling, why do you seem so upset over it? Are you going to help the original poster or just keep beating your chest?

to the OP: your HVAC system is 1 forced air system, recently updated, 2 programmable thermostats? Indicates a Zoned HVAC system. (Am I right? Is your HVAC system zoned?)

That said... I can only "help" the original poster if he lives in my service area and has a value of what this type of control is worth to him. I am able to come in person. "Helping" is not chatting in a forum board. I think our definitions are clashing.

People love to say how easy this is. This is an "in person job" 9 times out of 10.

Many who do not respond after the initial post have a sudden awakening and either drop the idea of what they are trying to do --- OR --- they call professional help.

So everything I have said thus far... including the little picture review has hints and tips. I'm here to do it for you... not teach you how. There are trade schools for that... maybe in 20 years you are lucky enough to have the understanding I have. "knowing what to do as well as what "not" to do."

There is a fine line... I merely attempt to elaborate why what you do is probably not going to work. (if you want to classify this as me beating my chest, I am OK with it.)

I service the Katy, Texas area.