I guess I would check the furnace end to see if they have the wires hooked up correctely there, or as you siad, swap the wires.

OTOH? try setting the thermostat to some obscenely high number, like 80 degrees.

It's sometimes the little obvious things that get me. What are the switches/settings set at? (I'm assuming that it's set ot "On" or "Heat"...)

Honeywell Thermostat Wizard

The furnace was fine till I took off the old thermostat, so I'm assuming the problem is up here, not in the basement. I tried setting it to 75, and am having no luck. I'll go back through the obvious things again, but I think I covered all of them.

So. Frustating.

Honeywell Thermostat Wizard

t red faced I should have thought of googling.

My Spymac web page is stuck in transition. Where else can I have free reliable webspace nowadays?

Actually, that wizard does not seem to cover my model. I walked through it anyway, with a model that seemed similar, but didn't get any big revelations. Off to ply the pliers.

Grasping at straws obvious stuff:

If it's programmable, are you sure you've got the time settings right, i.e. 9:30 pm Sunday instead of 9:30 am Monday, or suchlike?

It still might be worth taking a look downstairs just to see if the furnace breaker got tripped for some reason. Check the furnace switch (the one that looks like a light switch, but with a red plate), too.

Worse comes to worst, hook up the old one for tonight, and tape it to the wall.

Hooked up the old one. Had to try twice to get the damned wires to stay on the leads. Cross fingers that banging noise means heat for the first time in 8 hours.

While I am in the business of electrocuting myself, I must ask -- say you've got pretty wide-bore wires coming out of the wall, and thermostats, even old ones, don't seem to be designed for wires that wide. (We are talking 4mm wide, wide enough you couldn't use that size wire for an earring.) Is it legitimate to work up a kludge whereby you attach tiny fine wires to the giganto-useless wires, and then wind your fine pretty wires around the infinitessimal leads? And if I tried to do that, would I necessarily electrocute myself?

(Okay, yes to that last, since I know the wires are live and know where the fuse box is. So if I promised to turn everything off first, would it be a legitimate kludge? And, who designs these things? And how can I arrange for that person to be hanged, preferably with coax cable from a telephone pole?)

I'm not an electrician, but my understanding is that the thermostat wires are low voltage DC that simply open and close a relay; you won't electrocute yourself. As to why they used those large gauge wires, I imagine it was what they had on hand. I think (but don't hold me to it if your house burns to the ground) that you'll be fine with the fine wires.

Is it legitimate to work up a kludge whereby you attach tiny fine wires to the giganto-useless wires, and then wind your fine pretty wires around the infinitessimal leads?

You should be able to to attach thinner wire to the leads. You need to get some wire nuts at the Depot. Explain to one of the folks there what you want them for. They may have a better solution. (Or, if it can wait until Saturday, I can come up and take a look at it for you.)

Thermostats don't need the kind of cable it sounds like you found. 4 mm is an exaggeration, right? Heavy gauge wire is used for wiring the outlets and light switches (maybe 1 mm thick or so). The leads for the thermostat should be low voltage, like phone wiring, so in theory there's little chance of electrocution. However, it sounds like something is whacked there.