20yr old RUUD Furnace Not Turing On
Having problems turning on our 20 year old RUUD Furnace. I checked all the wiring to the thermostat and its good. The blower kicked on twice but for no rhyme or reason.
Its just not igniting however the pilot light is on. It has come on twice but then it just kicks off again. Im not sure what to do:help:
thanks in advance
at 20 years it is probably best to have it checked by service tech due to the possibility of a hole in the heat exchanger witch can create the danger of carbon monoxide poisoning
IF YOU SMELL GAS TAKE THE NECESSARY STEPS TO ENSURE THE SAFETY OF THE OCCUPANTS OF YOUR HOME AND CALL FOR HELP. BE CERTAIN THAT NO SOURCE OF IGNITION CAN OCCUR (INCLUDING LIGHT SWITCHES, MOTORS, ETC.). CALL 911. Open doors and windows to ventilate the gas.
If you are not a handy person, or have any doubts about this, do not attempt to fix this yourself. Call a professional. It is cheap insurance. A professional HVAC service technician will also be able to inspect your furnace for any other issues it may have that you may not notice - at 20-years old, if it has not had a checkup within the last two years, I highly recommend you do that. A furnace is nothing to screw around with if you don't know what you are doing, just to save a buck (the old "stepping over a dollar to save a penny" adage). If my whole post does nothing more than educate you so that you know what's going on then it is successful. My information is not intended to encourage you to attempt to do something that is inherently dangerous. It is intended to help you understand the system and make a decision by presenting my experience.
My Trane, 80% efficiency furnace, with the hot-surface electric ignitor, does that every once in a while (about 11-years old). The normal cycle for my unit is this: The thermostat calls for heat. The flue draft inducer motor starts and runs about 15-seconds or so while the ignitor heats up. Then the gas master valve (MV) solenoid operates to open the gas valve (an audible click). The ignitor should immediately ignite the gas in the burner box.
Now, there is a thermocouple probe that extends into the flame box (about 3-inches in length perhaps) right over-top one of the burners. This probe sends a signal back to the furnace controller confirming that the burners have ignited. If it does not get that signal, it closes the gas master valve (MV). The draft inducer fan will continue to run to ensure any gas present in the burner box and flue are evacuated up the flue stack and to the outside. After a prescribed amount of time (about 30-seconds?) it will open the MV again and try to light the gas. It will continue to do this cycling until I notice that it is screwed up and manually shut 'er down.
What I have found is that this thermocouple probe gets a little bit of carbon, perhaps, or oxidation on the surface and prevents the thermocouple from getting a good read of the burner. I suspect the circuit board is set to sense a threshold signal from the thermocouple probe, but since the probe is contaminated it cannot reach that threshold, and thus doesn't think the gas has ignited, even though I can clearly see (and hear) that it has.
The thermocouple is a sealed assembly consisting of the thermocouple element inside a stainless steel tube all mounted on a ceramic base. It is the exterior surface of this stainless steel tube that is of interest.
BEFORE GOING ANY FURTHER, SHUT-OFF ELECTRICAL POWER TO THE FURNACE. There may be a swich mounted right next to or on the furnace (mine is a light switch on a junction box) that you can flip to the OFF position. You may need to locate the circuit breaker for your furnace in your breaker box and throw that CB to OFF.
It is also recommended to turn off the gas. There should be a valve at the line before it enters the furnace that you can turn with a crescent wrench. The valve "handle" when in line with the gas line indicates open; The "handle" perpendicular to the gas line, it is closed. It needs turned only 90-degrees. It may be tight so secure the gas line while you turn the valve to ensure you do not torque the gas line. If you cannot turn the valve, then STOP AND CALL YOUR HVAC SERVICE TECH. This valve is necessary for isolating the furnace. The only other way of shutting off the gas to the furnace is the valve on your gas meter (outside the house), and/or the valve at the curb (underground, requires a special tool).
The order for isolating should be power (to remove source of ignition) then gas.
My Trane has two front covers - one above and one below. The upper cover must be removed to gain access to the gas valve, burners, and draft inducer. The lower cover exposes the return air motor and fan, and the controller (circuit board). The lower cover actuates a safety switch so that when removed the furnace cannot operate. This part of the furnace does not need to be exposed so leave the cover on. Only the burner area needs opened.
In my Trane it is a simple procedure to remove this probe. It is bolted onto the crossbrace that supports the burners with one 1/4" sheet metal screw, and has a single wire attached to its spade terminal. It is a total of about 3" long - it extends about 2" straight out then makes about a 45-degree turn for about an inch in order to extend right into the burner flame area. I disconnect the terminal by pulling it off, removing the screw, and carefully maneuvering the probe assembly out of the furnace. Be careful and gentle so-as to not damage the probe.
Lightly buff it clean with very fine steel wool obtained at any hardware store. I need only to polish it up without removing any parent material such that it is nice and clean. It would be a good idea to not touch the stainless steel portion of the probe in order to prevent bodily oils or other contaminants from your fingers from getting on it. Plus, oils from your fingers can lead to corrosion.
Carefully reinstall this probe - mine is keyed so that it is properly oriented so it fits only one way. Do not overtorque the sheet metal screw as damage to the ceramic could occur - a new one costs probably $50 at least, I would guess.
Reconnect the electrical terminal to the probe.
Verify that you have connected everything and did not disturb anything else.
I have made it a preventive maintenance item for me at the beginning of every heating season to clean this probe. I also use this opportunity to clean my furnace out - vacuum the dust and debris, inspect it, verify there is no corrosion that could indicate potential for cracks in the heat exchanger. If I see anything suspicious, I call my HVAC service tech. I also change the furnace filter at this time.
Reinstall the furnace cover.
Again, verify that you have connected, covered, and secured everything.
Again, taking care to protect the gas line, open the gas valve. Ensure you do not smell gas. If you do, turn off the gas and call your service tech. If you cannot turn off the gas and continue to smell it, take the necessary emergency actions for when you smell gas in your house.
Assuming no problems with gas, turn on the electrical power.
Verify that everything looks nominal.
Set a temperature on your thermostat that calls for heat and observe the cycle all the way through. If you notice anything awry, call your HVAC service technician.
Good luck. If you want photos of what I was referencing here, e-mail me.
Got to agree with mrairflow. A fact of life is heat exchangers crack and unless you're trained in inspecting them it's not a DIY job. Get it checked out by a qualified tech,takes me 15 minutes of labor or less on most furnaces.
As said it is a flame sensor but the manufactures don't recommend cleaning with steel wool or sandpaper. They want it done with something like scotchbright so you don't ruin it.
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