Thermostat has no voltage (Heating Only)

[techllb]

Hello all,

I just moved into a new place and the heater will not come on nor will the fan. I testing the voltage at the thermostat RH to G and nothing. I then went to the unit itself and tested at the control module and still no voltage between RH and G. I know the unit has power because the red led is blinking continuosly. On the unit it says it means "Normal: Call for Heat". Any help would be greatly appreciated. I know pictures help so I have attached a few.

 

[tylernt]

Blown fuse? Probably looks like an automotive fuse (glass cylinder or blade).

 

[philjafo]

Is the inducer fan running, hard to see but it looks like your missing the vacuum hose that connects to the pressure switch. Look for voltage between r and c, should be close to 24 volts ac. Turn the power off and spin the blower by hand, it should be very easy to spin and keep going for a few moments.

 

[techllb]

Blown fuse? Probably looks like an automotive fuse (glass cylinder or blade).

I checked the fuse and it's not blown.

 

[techllb]

I am not getting 24volts anywhere

 

[Hawk]

If that is for a fuel oil heater, have you bled the fuel line and mashed the reset button? If you have bled the line you may have to reset it more than once.

 

[Bill1031]

Look up the brand and model number of furnace online. Check trouble codes. That flashing red light is talking to you. If you have done this and that is where you are getting the normal call for heat? Then 99% of the time in a furnace that just quits heating. Check the igniter. When they are broke it is very hard to see. sometimes you can see a slight burn or crack. Replace it.

 

[brewchief]

Got a brand and model number?

 

[41ratrod]

Is there a transformer on the unit or is it made into the control board?
If it is a stand along transformer check for voltage power to it and from.
If it is made into the board it maybe bad.

 

[ForceFed70]

You have the meter set for AC volts right?

I would measure voltage right at the transformer. Confirm you have 120VAC going in and 24VAC coming out.

 

[acmikee]

check for 120volts. you may have to tape the safety switch shut. if now find it. if yes check for v at circuit board R to C. if yes check your safetys. if no find the transformers and check. lookfor a blown fuse in the circuit board....

 

[techllb]

ok I replaced the transformer. I have 120vac going into it and 24vac coming out. I have jumped the wires but nothing. With the thermostat on fan and nothing happening I switched it over to heat and the fuse blew immediately.

 

[philjafo]

Why did you replace the transformer? Blinking light on the board can't happen if it doesn't have any power. Which wires are you jumping out? Hopefully the fuse did its job and prevented you from doing any damage to the control board, but they are pretty sensitive electronics. I suggest you call a reputable service company before the repair gets more expensive.

 

[tylernt]

I switched it over to heat and the fuse blew immediately.

My guess is the thermostat is wired wrong, probably by the person selling the house. Verify the right colors of thermostat wire are connected to the right terminals inside the furnace, and also at the thermostat. If they are correct, the thermostat wire may be damaged somewhere inside a stud bay or joist bay. Or the control board is bad.

Also, some thermostats have jumpers or switches to configure them for heat pump mode and other things. Make sure they're all set right.

 

[mrobins297aaa]

ok I replaced the transformer. I have 120vac going into it and 24vac coming out. I have jumped the wires but nothing. With the thermostat on fan and nothing happening I switched it over to heat and the fuse blew immediately.

make sure the white wire from the thermostat is on the "W" terminal on the control module in the furnace and not on the "c" terminal...............white is not the common wire, it is the heating wire. Normally there wouldn't be any wires coming from the thermostat on the "c" terminal on the furnace control board.

 

[mrobins297aaa]

also if you created a dead short in that 24v circuit and have a old thermostat (not a digital) you probably smoked the heat intisapator inside the thermostat.
you'll need a new stat too

 

[metalTobman]

You did not mention what type of thermostat you have. More importantly though is if there is 24 volts a/c at the terminals on the circuit board. If not, you may have a fried board. No 24v at the board = no 24v at the 'stat.

 

[THEKID714]

I have a floor furnace that does not have any Transformer connected to it between the furnace and the Thermostat, and has worked perfectly for 30 years. But, now I need a new Thermostat and I don't know were to buy a new one

 

[THEKID714]

Why can't I find any information on thermostats that do not require power

 

[mrobins297aaa]

you must have a millivolt system there, look up millivolt thermostat.
ebay / amazon

 

[zmaxmotorsports]

Check rh to c on furnace board,g is for the fan not common.

 

[bobbyjean]

techllb- 5 wire's at stat?.... blue wire at stat is common... you can try 1-jump the door switch 2- unhook harness to hot surface igniter...replace fuse ...jump r to w at control board...fuse still good? 3-jump r to g at board fan should run 4-be safe

 

[crazy wheel]

Check rh to c on furnace board,g is for the fan not common.

Correct.....but he posted this 4.5 years ago

Looks like someone else hijacked the thread

 

[zmaxmotorsports]

Oops,didn't pay attention to the date.