I have a very old thermastat and the cover isn't there anymore. The problem is about 1 month ago the furnace was turned on by mistake and no problem it came on. Now since it's cold I turned the thermastat on and it won't turn the furnace on. The pilot is lit. Please help
Turn the power off to the furnace. Take your thermostat off the wall. Disconnect the red and white wire off the stat. Tie those 2 together. Turn the power to the furnace back on. If the heat comes on, the thermostat is bad. If it doesnt come on, then you may not have power to the stat. Possibly a bad transformer in furnace.
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Re: Thermastat and furnace
You should have 24 volts between yellow and white wires at the stat when the stat is set to heat and set as hot as it will go. burners should light first then 3 to 5 minutes later the fan motor should fire up. if burner doesn't light check the wires going into the top of the gas valve see if you have 24 volts arriving there from the stat. if you do then the gasvalve is probably bad. you can bypass the action of the stat by jumping red to white on 90 percent of the stats made and in a few seconds the gas valve should click open gas flow to main burner where pilot ignites it. another easy check you can do is flip stat fan switch to on. fan should come on at once. if not then you have either no high voltage to unit or no low voltage ( as in a bad transformer). if the fan comes on you know you have high volts and low volts...by cover i assume you mean the decorative cover but there second cover with the mercury bulbs and all is still there. if you have only the bare subbase then new stat time. sounds like an old furnace if it has a standing pilot, it should be checked for cracked heat exchanger by a pro with a n electronic carbon monoxide detector. NOT a diy item due to the real danger of co poisoning.
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If its a gas furnace it could be the heat sensor on the pilot flame unit. When the sensor is failing it stops telling the control that the pilot is lit properly and the furnace goes thru another start up sequence. You can try to scrape any flash and dirt off of the heat sensor rod to clean it or remove it and clean or replace the sensor or the pilot assembly. There are plenty or furnace parts on Amazon. The next most likely thing is the relay board is ready to fail that part is ~$80 but you need to get the part number right and be experienced with wiring. WARNING-DANGER B4 you do anything to your furnace Turn Off The POWER first! If there is no plug or switch near by, shut of the circuit breaker! If you don't know what any of this means then you are likely not a good choice to mess with this device Be Safe :)
This is what I found in the Simplehuman FAQ's. I had to wait about 30 minutes for the light to stop blinking, but it seemed to work for me.
If the pump is unresponsive or the blue light is flashing, fresh batteries should resolve this issue. Please power off the pump completely. Once the pump is turned off, remove the old batteries. Please wait for the pump to reset (until the flashing light stops and preferably letting it rest overnight) before you install the new ones.
Some one missed the wiring diagram. I believe its like this: L1 = Line 1 = (Hot all are same thing) Black Hi Blue Med Red LO Now usually the black is for AC and connects to a normally Open (NO) contact on the blower relay. The heater speed (either red or blue) go the the normally Closed (NC) on the blower relay and on one side of this wire or contact on the relay it goes to the heating blower thermostat on the furnace. The remaining wire (blue or red) you tape off. L1 also feeds the Run Capacitor on 1 side and the Brown wire feeds the opposite side
The white wire is Neutral and goes to the neutral on the main line.
If this helps you please rate me accordingly and good luck.
You make a good point about overheating on heat exchanger temp.
Since you don't have to reset anything for it to recycle, then I assume you have one of the newer forced draft furnaces.
There should be leds on the control board inside the furnace compartment that will blink a code to you, telling what the shutdown reason was. Blinks and code should be on a label inside the blower door panel, or inside the control box cover.
Let me know what they are, and I can give you more direction. I am assuming this furnace worked at some point, and no changes have been made (including closing of duct vents).
Check the intake and exhaust plumbing for any obstructions. I had same issue, turned out to be ice in the air intake plumbing on outside of house. This may be the problem. The pressure switch can be tested by pulling hose from purge motor that goes to switch and applying a small amount of suction. The switch should make a clicking sound.
#1 I would check that you actually have 3 phases connected. #2 I would also check the ground. There could be a loose ground, or depending on the installation, the ground could be defeated by rubber washers in flex lines. Fix this by running a wire from the casing of the water heater to the pipe, bypassing the flex lines.
#3 Replace the thermastat. The thermastat has the reset button on it.
#'s 1 & 2 are very minimal in cost. #3 is still affordable.