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My digital thermostat was blank this morning and furnace not

working. It worked last night...
My digital thermostat was blank this morning and furnace not working. It worked last night. We didn't lose power, and none of the circuits have been tripped. This is only the second time this season we've used furnace. It's about 20 years old.
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Answered in 8 minutes by:
9/15/2011
HotWired
HotWired, Mechanical Engineer
Category: HVAC
Satisfied Customers: 156
Experience: Recently earned degrees in, HVAC/R and Power/Building Management Engineer. Owner of Hotwired Electric Heating & Cooling.
Verified

HotWired :

HiCustomer

HotWired :

I am Rob and I will try to work though this with you.

Customer:

thanks

HotWired :

Try replacing the battery?

Customer:

Its direct power. I did just buy anew thermostat but havent installed it yet

HotWired :

turn the power off to the furnace

Customer:

ok have to go into the other room

HotWired :

remove the old thermostat from the wall

Customer:

im back. The old thermostat is off the wall already

HotWired :

make a note of thermostat wiring and mark the wires with the terminal letters

Customer:

ok should I just come back when done? it may be a few minutes

HotWired :

if you twist the wire from R together with the one from W or put them both under thr screw for R and leave the others aloan for now.

HotWired :

This should call for heat and start the furnace when you turn the power back on.

Customer:

sorry for the delay

Customer:

so twist r and w together?

Customer:

ok here goes

Customer:

nothing happens

HotWired :

Sounds like a bad control transformer

HotWired :

do you have a volt meter?

Customer:

no but I can run to the hardware store and get one. is it something I can do or should I can someone??

Customer:

i mean call

HotWired :

Well its not to bad

Customer:

ok i'm taking off to get a volt meter and get my kids at school be back probably an hour

HotWired :

can you find the control trans

HotWired :

before you go

Customer:

i don't know what that is /looks like

Customer:

sorry

HotWired :

in the furnace or outside on the electrical box with the service switch

HotWired :

it a metal cube looking thing

HotWired :

it will have to screws on it for the low voltage wires

Customer:

ok thanks. I am sorry i didn't realize how late it is. I will have to come back in a bit. Thanks for your help so far, sorry about this.

HotWired :

and two wires going in for 120 v

HotWired :

i will check back later

Customer:

thanks

HotWired :

do you have a time in mind?

Customer:

hi i'm back i tool the cover off i *think* I found it, it has a wire for 40v and also one for 280 but no 120,

Customer:

looks like the wire from the thermostat connects to it

Customer:

sorry thw onw from the thermo commects to the circuit board

Customer:

hi are you there?

HotWired :

I am back, some else jumping for a min?

HotWired :

this is it

HotWired :

40 va is the size of the transformer. the wires from it to t-stat should have 24 volts ac on them.

HotWired :

I have to run, b back in 10 mins

Customer:

ok i'll look for those

Customer:

ok from the circuit board there's a red and black wire running to the trans, both going into slots marked 24v, and a green ground wire running out of the 24v slot that the black wire leads into.. I can see the wires from the t-stat (red, green, white, yellow) running to the board, then the board is connected to the trans by those 2 red and black wires.

HotWired :

Do you have a volt meter yet?

Customer:

yes

HotWired :

can you check for 24 volt on the red and black wire terminals at the transformer?

Customer:

ok

Customer:

be right back

HotWired :

With the power on to the furnace

HotWired :

be careful

HotWired :

is this a gas furnce or electric?

Customer:

electric nothing

HotWired :

you have not get 24 volts?

Customer:

no

HotWired :

is there a box on the out side of the furnace with a switch on it?

HotWired :

sounds like a bad transformer!

Customer:

there isn't a box with a switch, but there are two large on-off switches on the front of the panel, i flipped those off/on when i did the same at the basement switch board.

Customer:

they are right on the front panel of the furnace

HotWired :

do you want to change the transformer or is it time to call in a tech?

Customer:

I think I better call someone, I'm probably getting in over my head.

HotWired :

A good harware store will have the trans.

Customer:

ok i'll probably get the trans and then call someone to install it, better safe than sorry when it comes to electricity

HotWired :

when you said 208 not 120 volts I new is was electric and not gas!

Customer:

thanks for the help- it'll probably go quicker now that i now what the trouble is

HotWired :

call around, it may be cheaper of the service truck than at the hareware store.

Customer:

ok thanks! :-)

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HotWired
HotWired, Mechanical Engineer
Category: HVAC
Satisfied Customers: 156
Experience: Recently earned degrees in, HVAC/R and Power/Building Management Engineer. Owner of Hotwired Electric Heating & Cooling.
Verified
HotWired and 87 other HVAC Specialists are ready to help you
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HotWired
HotWired
HotWired, Mechanical Engineer
Category: HVAC
Satisfied Customers: 156
156 Satisfied Customers
Experience: Recently earned degrees in, HVAC/R and Power/Building Management Engineer. Owner of Hotwired Electric Heating & Cooling.

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