Help with a gas furnace, Ruud Silhouette II???

[Russel Nash]

Hi all,

Thanks for ducking in here to read this post.

This is my mom's furnace at her house.

It will do this thing where we can hear the drafting (exhaust) fan spin up, then we can hear and see the ceramic igniter(s) light up, then the hear the valve for the gas open up and the burner(s) kick on....shooting a nice blue looking flame into the heart of the furnace.

Then 10 seconds later it all shuts down on its own. :veryconfu

My mom has had this furnace since 1997, and it seems like every year she has to have some furnace repair guy come out to service it.

Do you guys have any advice or tips?

[Heavy lead]

There is a flame sensor rod that makes contact with the flame usually on the opposite side of where the ignitor is, this usually needs cleaning using some fine sandpaper, or even a knife blade, it's a solid steel rod, straight or bent, with a ceremic housing with a screw holding it in the burner with a single wire going to the gas valve or the circuit board.
Should take care of it, it's a 5 minute job.

[flounderman]

thermocoupling not staying hot enough or plugged pressure regulator would be where I would look. watch the flame on the pilot light that plays on the thermo coupling. If it does not have a pilot light, check the regulator. all the gas I have worked on have thermo couplings. until it is hot enough, it keeps the gas shut off so if the pilot light goes out there will not be a gas leak.

[Jeffrey]

Sand the rod CAREFULLY. It is extremely brittle and will break like glass. You should be able to see the rod through the window into the combustion chamber. The end of the rod should be in the flame when the furnace ignites. A wire is connected to the end of the rod that is outside of the combustion chamber. Check the connections for corrosion / dirt. Check the furnace for a GOOD ground. Lack of a good ground connection will give problems.

[Jeffrey]

PM me with the model #. 26 years I've been messing with HVAC.

[dragon813gt]

Cleaning it may or may not fix the problem. The RUUD flame sensors have a habit of working for a little after cleaning and then dying. You need a multimeter that will read microamps to check it out. Put the meter in line with the flame sensor. You need a minimum of .5 microamps for the board to recognize it has flame. Typical running reading are from 2 to 4 microamps. Clean it up and see if it works.

If it's a propane furnace just buy a flame sensor anyway. They take a beating from the propane. The sensors are cheap and I replace a few a week across all makes/models.


Brought to you by TapaTalk.

[Bill*]

@jeffrey
"26 years I've been messing with HVAC. "
And you're from Kiln, Mississippi?
What're the odds? :mrgreen:

[Jeffrey]

Originally from New Orleans. Moved to Rhode Island in '86 (wife is from RI, now southern by injection). Spent one winter there, put myself through HVAC school so I could bring my little red wagon back down south. Moved to Kiln after Katrina: now 122' above sea level. BTW, You can keep those yankee winters.
Dragon has a good point. BTW those are DC microamps (milliamps?).

[MT Gianni]

I would clean the flame sensing rod with a $20 bill, New enough to be abrasive but not overly so, you just want a good polish without scratches. Then double check the ground on the ignitor board by loosening and tightening the screws holding it to the furnace case. Any vibration or rust in that area will impede grounding. Lastly as long as you are there and have it in front of you find the rubber tubing that runs from the inducer fan to the pressure sensing switch, cut off the portion that is on the metal port + 1 " and reattach it. A crack there will also put you out of business though it will never get to the ignitor stage.

[Russel Nash]

okay, thanks!

a bunch guys!

[Wayne Smith]

I have a gas furnace. Know essentially nothing about it. Get it serviced yearly. To me it's cheap insurance, preventative maintence.

[Russel Nash]

It was the flame sensor. Thanks guys!

[markinalpine]

It was the flame sensor. Thanks guys!

Glad she's back up and running. I had to have the sensor replaced several years ago. Last winter, different house & furnace, but with the same type of system, we kept having low gas pressure and my furnace would either go out, or not even start after the ignition sequence. The utility had the problem in this case and got it fixed after just a few, cold days.
Mark [smilie=s:

[Freightman]

Just had the same problem, plus the controller was out, thank goodness for home protection policy, the spring started out good the dishwasher stopped, got it replaced, then when it was 106, the air conditioner (24 years old) went boom, then all was well when we replaced the unit. Not opened the closet where the hot water heater was, 3" deep in water, the water heater I bought cost $198 when I purchased it this one same brand and capacity cost $750 go figure. I thought nothing else can happen, wrong then the heater wouldn't heat, well thought I was through, but no the cook stove burned up,now I am cooking on the grill outside. Went shopping for a new cook stove and I have the papers on the old stove bought in '87 $250, the cheapest I found in looking was $500+ for the same features, we haven't had any inflation have we. O did I mention my 25 year old microwave quit and the air conditioner on my24 year old Ford PU quit, I am afraid to go to the range might get shot with my luck this year.

[firefly1957]

I have had the same problem with the flame sensor , my flame sensor only has a single wire and the ground sometimes is the problem make sure the plate the flame sensor is mounted to is well grounded if it has a single wire.

Each fall I had the same problem with ignition on my boiler since adding a copper ground wire I have had no troubles in 4 years. The plate the flame sensor is on is removable to remove burner tubes so I added a small jumper to ground from it.

[MT Gianni]

I have had the same problem with the flame sensor , my flame sensor only has a single wire and the ground sometimes is the problem make sure the plate the flame sensor is mounted to is well grounded if it has a single wire.

Each fall I had the same problem with ignition on my boiler since adding a copper ground wire I have had no troubles in 4 years. The plate the flame sensor is on is removable to remove burner tubes so I added a small jumper to ground from it.

The flame sensor makes the circuit through flame rectification. The flame changes the AC current out of the flame sensor to DC completing an electrical circuit with only half a sine wave. The control module reads this and tells itself the fire is going. As such, the flame rod itself must not be grounded but the burner the flame grounds to must be. It usually completes the path through the frame to the control mounting screws and back to the board. Moist climates can sometimes use a little help due to corrosion.

[firefly1957]

MT Gianni Thanks that makes sense I knew it was not a thermocouple by its build.