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Bill P.
Bill P., HVAC Mechanic
Category: HVAC
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Experience:  Oil / Gas / A/C / Hydronics
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Just installed a new thermostat and now the heat wont turn on

Resolved Question:

Just installed a new thermostat and now the heat won't turn on.

Submitted: 6 years ago.
Category: HVAC
Expert:  Bill P. replied 6 years ago.

Bill P. :

Hi there

JACUSTOMER-4u2p2m69- :

Hello

JACUSTOMER-4u2p2m69- :

I am having issues with a honeywell thermostat I just bought and installed

Bill P. :

What type of furnace do you have? With a/c or heat pump?

JACUSTOMER-4u2p2m69- :

I don't know the brand, it is a gas heater

Bill P. :

How many wires were there to put on the new thermostat?

I'm wondering if you maybe blew a small fuse in the furnace?

Is it a normal furnace?

JACUSTOMER-4u2p2m69- :

There are 5 wires and I'm going to go up and look at the furnace now

Bill P. :

Ok, when you do, find the main power switch to the furnace and shut it off. Then find where the thermostat wire goes into the furnace, it will connect to a computer board of some sort, on that board there will probably be a blade type fuse, 5 or 3 amp

Looks like a automotive type

Bill P. :

http://static.letsbuyit.com/filer/images/uk/products/238x178/152/10/sealey-automotive-fuse-3amp-pack-of-10-15210536.jpeg

That is a link to a picture of the fuse

JACUSTOMER-4u2p2m69- :

Comfortmaker is the type. It is in the attic

Found the computer board...now what?

Bill P. :

Ok, try and have a look for the fuse

Bill P. :

I put a link there above. That is likely what you are looking for

JACUSTOMER-4u2p2m69- :

Is the fuse going to be behind the panel with all the wires?

Found it..now what?

There's a number "5" on the fuse and and it's plugged into a terminal labeled F1 if that means anything

Bill P. :

Yes, that would be the one

Remove it (power is off right?) and have a look

If it is blown, the little metal strip that connects the 2 sides will be broken

JACUSTOMER-4u2p2m69- :

Yes, power is off, and the two little pieces of metal in the middle that are shaped like a "z" are not connected. Is that what we are looking for?

Bill P. :

Yes, that is right. The z should be solid from one end to the other

JACUSTOMER-4u2p2m69- :

Oh, good to know. So, does that mean we just have to replace this and we should be good to go? and where would we find this piece? Home depot? or radio shack?

Bill P. :

More than likely yes, the fuse is there to protect the rest of the circuitry. So it will likely be fine with a new fuse

Either one, but I would try radio shack first. Automotive supply store also would be a good place to try

JACUSTOMER-4u2p2m69- :

Once we get the new part, should we reinstall the new thermostat? or just put the power back on?

Bill P. :

Sure, if that was your plan in the beginning; but if you ever have to mess with the thermostat wires again, or any wires for that matter, just turn off the furnace power first. That way the fuse will not blow

I would leave the old thermostat on for now, put the new fuse in and make sure everything works. Then shut power off and put the new thermostat on, power on and you should be good (the new thermostat may need to be programmed to your preference)

JACUSTOMER-4u2p2m69- :

Great! thanks for your help. So, basically we just blew a fuse and that is why it won't work?

Appreciate the help

Bill P. :

That is the low voltage circuitry fuse, so since the power was still on when you were changing the thermostat, the wires touched each other and caused a short, so the fuse just pops

You are welcome. If for some reason that doesn't get you going you can come and carry on the conversation later

JACUSTOMER-4u2p2m69- :

Well, thanks again!

Bill P. :

Good luck!

JACUSTOMER-4u2p2m69- :

Replaced the fuse, and it still won't work

Bill P. :

Are you using the old thermostat?

JACUSTOMER-4u2p2m69- :

We tried, but can't get the wires to connect where they are supposed to.

We had already put in the new one before we knew it didn't work
Bill P. :

Does anything work, like the fan on button?

JACUSTOMER-4u2p2m69- :

Nope, tried that. We switch heat on, nothing

Put fan on, nothing. Even tried a/c...nothing

Bill P. :

There are 5 wires right?

Before we get too far, maybe check the fuse again

JACUSTOMER-4u2p2m69- :

Upstairs connected to the furnace, it is a

red to r

white to w

yellow and another red going to y

green going to g

another white and copper going to c

Yet by the panel we have 5 wires

And the fuse is still good

Bill P. :

2 of those wires will be going to the outside a/c unit

What do we have for wires at the thermostat?

Do you have the door back on the furnace while you were trying it? (there is a door cutoff switch on the furnace)

JACUSTOMER-4u2p2m69- :

A "c" wire that the instructions on the new thermostat say not to use; blue, yellow, green, red, and copper. Old thermostat had copper plugged into "c" and blue was tucked into wall

No we didn't. We will try that now

Bill P. :

Ok

JACUSTOMER-4u2p2m69- :

Should we plug in the blue wire even though it wasn't plugged in before?

Bill P. :

No leave the blue unhooked

JACUSTOMER-4u2p2m69- :

Ok..will do

Bill P. :

And leave the copper unhooked from "c" for now too

JACUSTOMER-4u2p2m69- :

We don't have a "c" on the new thermostat

Bill P. :

That makes that easy then

Bill P. :

Do you have a white wire for W by the thermostat? I imagine you do, you just didn't list it

JACUSTOMER-4u2p2m69- :

Yes

Bill P. :

Ok, so with the door on the furnace what is happening and the power on

JACUSTOMER-4u2p2m69- :

Putting the door back on now

Then going to flip the power

Bill P. :

Ok

JACUSTOMER-4u2p2m69- :

Woohooo! it's on!

Bill P. :

Nice one

JACUSTOMER-4u2p2m69- :

Are we ever going to have to plug in the blue? or are we good for heat and a/c?

Bill P. :

No, you won't need the blue. Its not hooked up at the other end

Yep, with the 4 wires you should be good

The "c" wire is for 24 volt power for the thermostat (instead of running on batteries) but I guess your thermostat just doesn't bother with it

JACUSTOMER-
That makes sense

Thanks a bunch!

Bill P. :

You are welcome!

JACUSTOMER-4u2p2m69- :

Have a good night!

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