Any heating and cooling Guys out there? I have a question

-
68383GTS

68383GTS

Well-Known Member
Joined
Nov 15, 2007
Messages
7,498
Reaction score
951
Location
East Peoria,IL
I have a Rheem Classic 90 Plus furnace.Here is the issues it kicks on and the pilot lights but then goes out.The pilot flame may go out after a few seconds ,or it will light right away and go out after a few minutes or several minutes.Sometines it takes 3 or 4 times before it lights up.Woke up yesterday and the house was 62,the wife was not happy...LOL I just hate electronic things.Had a electronic dryer and it mess up too.It seems the more simple things are the longer they last.


Thanks,Jim
 
There should be a flame sense rod that sticks into the flame so it knows when it is lit. Take it out and lightly sand it. Pop it back in and give it a try. They usually build up some scale on them and are less effective.
 
Jim, furnace is probably going out on flame failure(not seing pilot on ) which would be the flame rod , metal rod that's by pilot flame, you can clean it with acetone or a quick wire brushing , also on furnace is the trouble shooting lights on front panel cover, usually has window on door to see blinking light ,when it fails count blinks sometimes a pattern ,then shut off furnace ,remove cover and on back of door should be trouble light codes ,will tell you what problem is , these furnaces are good ,but do require some maintenance, as they do produce acidic condensate , have various water traps in furnace that should be flushed and cleaned ,hope this helps, Mike
 
What these two members said, or the thermal coupler (metal rod that's by pilot flame) has went south on you, easy repair, it run's to your gas valve and if it is bad it can be removed and replaced easily if a cleaning does not help.. Good to see many lines of tech help here :color:
 
The pilot is a small burner so it has small openings in a barrel/tube just behind that flame. Those air for proper fuel air mixture. I'll agree the thermo coupler is the most common fault but... while you're in there, blow all the dust away from the pilot burner assembly.
We've had a vent free gas log fireplace for about 10 years now. Never have replaced any parts. Have had to clean the pilot burner area a few times.
 
Some newer high efficiency gas burners use a flame sensor (electric output) rather than the more common thermocouple (thermal expansion). Either way, this is where I'd start. Try a Google search... if it's a common issue there should be some clues out there.
 
This furnace does NOT have a thermocouple , thermocouples are used on standing pilot furnaces, this model you have has a spark ignition to ignite gas. The members who suggest the flame sensor are correct, a quick fix is a cleaning of the sensor with fine sand paper emery cloth is perfect. But for the cost of the sensor ($15-$25) get a new one ASAP or it may just happen again. Depending on the model furnace you have it could have a two stage gas valve as well. My job, HVAC Foreman
 
The flame sensor needs to be replaced then. A cleaning likely will not fix it. If I am correct the sensor comes as an assembly , igniter, sensor, spark ETC. Wouldn't hurt to do them anyway, cheap insurance. Getting in deeper the gas valve could be dropping out before main ignition as it is timed through the circuit board or the board it self. Trouble shooting I go for the easy and least expense first. Tough trouble shoot from a distance. But flame sensor is likely your issue. Do that first. I hate tossing parts at something till it's fixed but my best guess from here is the flame sensor/pilot assembly.
 
Try this if you want to check yourself. Hope its not the board, likely the sensor.

http://www.doityourself.com/forum/gas-oil-home-heating-furnaces/488998-rheem-classic-90-burners-7-seconds-then-stops.html#ixzz2LNMc0vm7>>
 
it might be helpful to understand how these flame sensors work. They are a very low current, very high impedance circuit. THIS MEANS that any dirt, moisture, corrosion, etc, that causes a "partial short" form the sensor circuit to ground will disable them.

It also means that the ground path from the control box to the piece of the burner out of which the flame is produced MUST be good.

This is known as "flame rectification" and is based on the idea that a rod in a flame which has a (fairly) high voltage AC signal, will rectify that AC into DC. This DC can be detected by the control box on the order of JUST A FEW microamps. That is several MILLIONTHS of one amp

Also, the wire/ rod connection inside the ceramic mount can break, and can become intermittent due to heat/ cold thermal cycling.

As suggested above, I'd buy a new sensor, and insure that the burner to box ground path is good and tight.

Check the documentation on your furnace. Many of the control boards / boxes nowadays have a 'blinking LED" diagnostic error indicator which might get you on track.

Also be aware of "how it works."

In general, you have several safeties which all have to be "good."

Generally you have

A manual reset vent switch safety (high temp) which "kicks out" and must be reset if the vent is plugged or draft blower fails or other cause of "not venting" Sometimes called a "spill switch"

Sometimes, a manual reset high temp safety

Always, a recycle high temp (limit) switch if the blower quits or plugged filter

Vent pressure switch, which detects if the vent/ draft blower is generating enough vacuum/ pressure

Of course "flame proving" which is the rod / sensor in question

Do I have to say it? NEVER attempt to bypass any of them.
 
Ceramic only for a HSI system, his is a spark ignition, as well, correct there are many safety situations such as Vacuum switch, roll out switch, flame rod, vent switch etc. But considering that the furnace attempts to light tells me all these safeties are being met and the gas valve is opening. It would not try to fire if any of the safeties are not satisfied. These are wired in a series one locked out or not functioning and it would not fire. Trouble shooting skills 101. Its sparks , it lights...doesn't stay lit, so all else is good, it will be flame sensor seeing no flame after being lit (mili seconds after) or back to the board where this is all times out via PC board. Yes, never bypass any safeties on the furnace except for trouble shooting, never leave a safety bypassed.
 
67Dart273 is right about the flame sensor. They are very sensitive. Most HVAC trained professionals will frown on sanding the sensor. If you clean it with anything, use a soft piece of paper, like 600 or better yet, a coarse scotch brite pad until it is bright without discoloration.

This is only a band-aid. If the sensor is fouled, it should be replaced. You can clean it to get you by, until you have replaced it.

I was not able to find the diagram for your model online, but some models have a trouble code from the LED light on the PCB panel, down below. You should be able to see the LED through the sight glass, if this is the case. Do not take the door off to read the light. Just pay attention to the series of flashes and relate them to the legend that came with the furnace manual or legend label somewhere on the furnace, usually on the door.

If you can't see the light, if the sight glass needs cleaned, you can remove the door and clean inside and get the thermostat to call the furnace again, to instigate the trouble code cycle light.

If you do not have a legend for the codes flashing, or you do not have a code flashing on the LED light, you can still diagnose the problem, but the first thing you need to do is clean everything.

Pull the burner assembly out, blow it off, vacuum it, wipe it down, vacuum out everything inside. Replace your filter (this will affect other things, including other sensors that can short cycle your furnace) and try it all again.

There are carbon monoxide detectors, also known as flame roll out sensors, these will also detect any orange flames being emitted, even in short bursts, from dirty burner assemblies. You can't properly clean a burner without removing it.

Clean everything first, try replacing the flame rod sensor. if that does not fix it, test the exhaust pressure switch by disconnecting the hose while it is running to see if it immediately shuts the burner off (and possibly the blower and exhaust motors).

You might also want to check your exhaust chimney to see if it is even partially blocked. Lint buildup or birds nests, snow, etc., can cause the pressure switch to do what it's supposed to do, which is tell the system to shut down, sometimes this happens once the ignition is proven and you have flame.

Your best friend is going to be the LED code flashing. If you open that door to watch it, instead of using the sight glass, it will reset the computer and has no memory, so you will need to turn the thermostat up/ on again to call the furnace on, again, before diagnosing it. There is a switch on the access door that is tripped, that turns the computer and the system off, when the door is off/ open.
 
Once you get the problem resolved, you may want to do an over all tune up on it.

I just went through the system in my house that has butchered vent ducting, but I managed to get the system to cycle in a reasonable frequency for my house and temp climate.

Adjusting things like the thermostat's anticipator, keeping a clean filter and clean furnace inside and out will help extend the lifespan of the heat exchanger, the ignitor and cut down on your utility bill.

Each safety switch is there for a reason. Some of them are adjustable and should only be set once, like the heat exchanger max temp switch. The anticipator on the thermostat, when adjusted properly on a clean system with working components, is probably the most important thing you can do to a system to extend its life, along with keeping a clean filter in it, so the heat exchanger can cycle properly without overheating quickly and without cycling too frequently.
 
marksmopar1 said:
Ceramic only for a HSI system, his is a spark ignition, .
Click to expand...

I don't get what you are saying here. Hot surface, flame sensors, and spark ignition electrodes are all mounted in ceramic insulators/ mounts. What I was getting at is that the sensor wire can sometimes come loose internally and lose reliable connection.

marksmopar1 said:
These are wired in a series one locked out or not functioning and it would not fire. Trouble shooting skills 101. Its sparks , it lights...doesn't stay lit, so all else is good, it will be flame sensor seeing no flame after being lit (mili seconds after) or back to the board where this is all times out via PC board. .
Click to expand...

I'm speaking more of an intermittent problem. An example is a shakey vent barometric switch, or a vent problem "right on the edge" causing the switch to dance in and out. I've seen both. What can happen (with inexperience) is that the burner may light for just a moment, and the "puff" is just enough to trip the baro switch offline.

I've learned, over the years I worked on this ****, not to make assumptions. I also, as a rule, never "threw parts" at a problem. But vent barometric, and vane and other duct pressure switches, frankly, can be a real PITA.

When I was doing this stuff, many controllers did not yet have diagnostics. Some of the old crap like the GE rooftop units had "relay logic" that was more than a nightmare.

Another one I hated, and we had a few thanks to a long gone contractor, was an odd electric furnace I can no longer remember the name of

They used "Pi rod" type heater elements, and DC control circuits. When they worked, they were fine. When they started to give trouble, they were ridiculous. This was before Al Gore invented the internet.

One of thes, I actually pulled the controls out, and converted to AC controls with plain ol' heat sequencers. Took longer 'n I thought it would, and we made no money on that deal.

Some of the old Honeywell flame rod based burner controls for the big "gun" 200-400K BTU rooftops was absolute crap when it gave trouble.

I just last month had to order a new board for my Carrier 80%. The good news is that there are now aftermarket boards that are a lot cheaper than Carrier wants to rip you for. This is one good thing about the internet.
 
67Dart273 said:
it might be helpful to understand how these flame sensors work.................
Click to expand...

Not to hi-jack the thread but are these type of sensors used in gas dryers also? The reason I ask is a dryer I replaced a while back would heat up a glow plug deal, the gas would ignite, plug would go dim, then fifteen or so seconds later the gas would shutoff. But then again sometimes it would run just fine.
 
Some of the older dryers had a lashup with a temp sensor. I have not kept up on dryers. If it fires for fifteen seconds and dies, it's much more likely to be a plugged vent problem, line plugging something like the blower wheel, or a blower wheel loose on the shaft

In the late eighties I maintained laundry gear for several local laundries owned by a family. I LOVED the Maytag stuff. Took me all of about 1 minute to pull the front cover and remove the drum. You could clean those out in nothin flat. I've seen all kinds of stuff in the blowers and ductwork, including several calibre of live ammo

There are several ways, typically, that flame rectification is set up

Some is right off the main burner, that is, there is no pilot

Some light a pilot first, "prove" the pilot then allow the main to fire

Some are spark, some are "hot surface," or a glow device

And, some have the spark or hot surface device combined into the sensor. This involves a tricky internal circuit. BE CAREFUL with hot surface as these have line voltage (120VAC) on them. Keep your fingers and tools away from them.

Flame rectification is pretty much the "de facto" method. It is pretty reliable and really safe. Pretty much "fail" in safe. Years ago, they tried photocell, which does not work well with gas or LP and Carrier used to have a crappy thermostatic pilot sensor deal that was a REAL PITA Thermocouples were "OK" but Honeywell made a BUNCH of gas valves "back when" that could fail even though the pilot safety was "dropped out."

Once in awhile, tho, you will find a gas valve STUCK OPEN. Last one I came across was on a gun burner conversion in an old old convection furnace, converted from oil or coal. It was a cold day, and had got up to the middle 80's in the office. "The girls" could not get the thermostat to kill the heat. I went downstairs and the burner was wide open. Killed the main power and it was.........WIDE OPEN.

If this had been a weekend and left on, we'd 'a had a fire.
 
Maytag is where its at. My house came with a new washer and dryer set. I gave them to my mom and kept my '76 Maytag tanks that I bought for $80 for the pair. They are indestructible.
 
I took it apart and found a second flame sensor.I cleaned the second flame sensor and blew everything out.The furnace seems to be working alot better now.

Thank You for all the Help....
 
Yes before I met the Wife I kept it at 65-66 all winter now she likes it at 70.I am always turning it down to 68...LOL
 
Great! The old second flame sensor hidden in the furnace trick.. LOL
Easy and cheap! :)

Oh and by the way, cleaning it is a fix...although a temp one just to get ya going and the wife happy :), I would still replace it and or both as they really are not that expensive.

HVAC Foreman is what I do for a living....Seen them all over the years, 9 Million sqft of buildings area I do in this city... :) Keep smile'in!
 
After I cleaned the furnace it worked perferct for a day and a half.Then it started doing the same thing.I had a Heating and Cooling Guy come out twice and it still isn't working right.The Flame goes out and when the furnace does run it shuts off before reaching the temp set on my thermostat.I am going to go and see if I can find a flame sensoe today and replace the old one.
 
Check Ebay. I would not have waited this long........

Why didn't the so called HVAC guy fix it. WHAT DID HE DO?

Did he check the flame rod current? Position of the rod? Do anything except stand there and say "yup?"

Why didn't he replace it and WHY DIDN'T he have one on the truck?

Ebay, not necessarily the correct ones, check year, make model color, etc etc etc

http://www.ebay.com/sch/i.html?_from=R40|R40&_sacat=0&_nkw=rheem+flame+sensor&_sop=15
 
You must log in or register to reply here.
-

Back
Top