I had the experience of having to clean mine last night. I had heard that the wire can get deposits on it and the symptom is usually that the burners light and then shut off right away. Sure enough, at 12:30 AM I realized it's getting chilly in the house, checked the thermostat and it showed it was commanding heat. Furnace was lighting and shutting off repeatedly. Polished up the wire with some steel wool and it's back in business. So is this just a routine maintenance item? It's a 10 year old Trane, and I'll admit I've never cleaned the sensor. Never had to clean one before though. The burner flame looks normal, not burning yellow and sooting up the probe.
Gas furnace flame sensor
- Thread starter Dave Sherman
- Start date
It happens. It could go for the rest of that units life and not need it again.
Maintenance? Maybe, if it's easy enough to get to and you never want to experience that situation again.
Maintenance? Maybe, if it's easy enough to get to and you never want to experience that situation again.
I never had to clean the one on the circa 1994 York furnace at my old house the entire time I lived there till I sold it in 2017.
I have had to clean the one at my mom's house which is a Janitrol once or twice. Unit is the same age.
Difference is, the York is installed in the basement, Janitrol is installed in the attic. I wonder if that might have something to do with it, attics are dusty.
I have had to clean the one at my mom's house which is a Janitrol once or twice. Unit is the same age.
Difference is, the York is installed in the basement, Janitrol is installed in the attic. I wonder if that might have something to do with it, attics are dusty.
Yes, you should clean the flame sensor every year or two. When my Trane furnace was installed in 2010, it came with a courtesy annual inspection/maintenance service for two years. I shadowed the HVAC technician during both inspections and noted everything he did and how it was done. I now perform the service every other year myself and it only takes 45 minutes to complete. The best way to clean the carbon residue off of the flame sensor is with a green Scotchbrite scrubbing pad.
It most likely depends on your gas supply, how "dirty" or clean the gas is, etc.
Are you on Propane? My house was built in 1996 and we have a buried propane tank. There's almost 30 years of build-up of the oil/residue that comes along with propane in the tank. When I neglect to have it refilled in a timely manner, i.e.: we get down to 1 or 0%, we can smell the nasty oil/etc burning on the water heater pilot.
This has fouled my pilot light burner components several times in the last 7 years (we have been there 8, installed a new water heater in Oct 2015). I attribute it to this oily mess that is probably contaminating the pilot. What happens is we lose the pilot and run out of hot water unexpectedly. I have to clean it every 12-18 months, I replaced the entire pilot / burner assembly about 8 months ago.
Which reminds me.... I need to call and get some propane delivered....
Are you on Propane? My house was built in 1996 and we have a buried propane tank. There's almost 30 years of build-up of the oil/residue that comes along with propane in the tank. When I neglect to have it refilled in a timely manner, i.e.: we get down to 1 or 0%, we can smell the nasty oil/etc burning on the water heater pilot.
This has fouled my pilot light burner components several times in the last 7 years (we have been there 8, installed a new water heater in Oct 2015). I attribute it to this oily mess that is probably contaminating the pilot. What happens is we lose the pilot and run out of hot water unexpectedly. I have to clean it every 12-18 months, I replaced the entire pilot / burner assembly about 8 months ago.
Which reminds me.... I need to call and get some propane delivered....
Good to know, it had occurred to me I might want to buy a spare ignitor too.
25 or more years ago, ago York (maybe some other brands too) used a spiral ignitor. This failed on my furnace when it was 6 years old. The new ignitor from York is a different design, that one lasted the next 17 years till I sold the house.
dnewton3
Staff member
As HBD mentioned, it's a function of how clean or dirty the fuel source is. That in mind, there's no "maintenance schedule" that going to be a set value for every furnace owner.
If it took 10 years for the OP's furnace to get to a state of needing the flame sensor to be cleaned, then there's no reason to clean it every other year. Remember, everytime you disassemble and assemble something like a furnace, there's a chance of stripping screw holes, breaking an electrical contact tab, shorting out the control board via static electric charge, etc .... So going into the furnace more than necessary is asking for some other problem to show up (a result of the Law of Unintended Consequences .... you break item B in an attempt to fix item A).
Since it took 10 years to misbehave this time, I'd not touch it until perhaps 2030 (seven years from now). That should give a little bit of cushion without it being over-maintained.
In my previous home, I had a Carrier h/e furnace that I didn't have to touch once in 16 years. If it ain't broke, don't fix it. The installers tried to sell me on an annual contract; what a waste of money those are!
If it took 10 years for the OP's furnace to get to a state of needing the flame sensor to be cleaned, then there's no reason to clean it every other year. Remember, everytime you disassemble and assemble something like a furnace, there's a chance of stripping screw holes, breaking an electrical contact tab, shorting out the control board via static electric charge, etc .... So going into the furnace more than necessary is asking for some other problem to show up (a result of the Law of Unintended Consequences .... you break item B in an attempt to fix item A).
Since it took 10 years to misbehave this time, I'd not touch it until perhaps 2030 (seven years from now). That should give a little bit of cushion without it being over-maintained.
In my previous home, I had a Carrier h/e furnace that I didn't have to touch once in 16 years. If it ain't broke, don't fix it. The installers tried to sell me on an annual contract; what a waste of money those are!
I agree that maintenance contracts are not cost effective to anyone who has basic mechanical abilities (that would be ~95% of the members on this board). In case anyone is interested, here is the procedure used by many HVAC technicians to perform an annual maintenance service on a gas furnace:
- Check operation of thermostat functions.
- Check operation of emergency cut off switch.
- Vacuum or blow out dust within the air handler cabinet.
- Inspect air filter(s) and replace as necessary.
- Test continuity/operation of access door safety switch.
- Investigate any trouble codes displayed on the IC control board LED.
- Clean soot from the flame sensor wire probe (and spark igniter, if equipped).
- Verify proper operation of exhaust gas induction blower and vent stack not blocked.
- Test operation of induction blower vacuum sensor diaphragm (by disconnecting and sucking on rubber tubing).
- Check continuity on the rollout flame sensor and various bi-metallic switch overheat sensors.
- Visually inspect gas burners and heat exchanger.
- Verify the operation of the hot-surface igniter.
- Observe flame pattern and color.
- Verify normal operation of (single speed, 2 speed, variable) air handler blower fan.
- Inspect physical condition of starter capacitor(s).
- Flush out condensate discharge PVC pipe with bleach and water.
- Check freon pressures and compressor operation on condenser unit if Heat Pump/Dual Fuel unit.
Yes. I've had it happen twice. My attempts to fix it the first time didn't fully work, so I had a tech do it. I watched closely and was successful the second go around. It's a 23 year old Rheem.
dnewton3
Staff member
Yes - that I agree with in principle.
Most of your list is NOT going to prevent a failure. I'll dissect one at a time ...
Doing "checks" is just moving the switches or pushing buttons. None of which does anything "preventative" in terms of preventing a future failure. Anytime a homeowner touches the thermostat they essentially do the same thing. This is a "feels good to watch him touch the device" item. It prevents or fixes nothing. If the thermostat were to fail at some point in the future, nothing the tech did was going to prevent it by "checking it".
Again, checking a switch does what, exactly? How many times do techs find a bad "emergency switch"? And what is an "emergency switch" anyway? Are you speaking to the service switch on the side of the furnace that cuts power to the unit for work? And just how is it that a homeowner can't check the function of a switch (presuming it's exterior to the unit)?
This is a feel-good item; it does nothing to prevent a failure. Dust isn't the cause of any major failure modes.
Man oh man, if a homeowner can't change their own filter, then they should live in a condo where all maintenance is included.
Again - what failure mode does this prevent? If the switch is closed, the furnace runs. Assuming the homeowner isn't just taking the door off and defeating the switch for the joy of running the furnace, why is this a service worth paying for? And how many times has a bad switch been discovered? This is probably one of the lowest failure modes of any furnace malfunction. If the door is on, and the furnace runs, then leave it alone!
Those trouble codes are very helpful when there's a problem. When there's a problem, a service call is very prudent. But assuming all is running well, there will be no problems with the furnace, and hence no codes present, and therefore no need for a service call, which means no service tech. Including this in the "preventative maintenance contract" has ZERO gain for the customer.
Yes, this can be beneficial. But, it may not be necessary for a decade or longer (my example of 16 years with no issues). Why have an annual service contract for something that may not happen but once a decade?
All modern furnaces have safety protocols written into their operational logic that does this by looking at the pressure differential at the pressure switch, inducer amps, etc. A service tech is only going to watch the furnace go though it's ignition sequence and if it's all good, he does NOTHING else. If something is wrong, then the furnace will set a code and the code can be read by the tech. Again, a service call would be prudent, but a maintenance contract doesn't prevent any failure here.
Aka the pressure switch. It either works or it doesn't. Yet again, the furnace has programming to detect the failure; it won't make the dP if there's a leak.
The only "preventative" measure would be a true part replacement. This would be like changing out a fuel line on a car even if no evidence exists to warrant the change. By the way, this "diaphragm" test is assured in the above "induction blower / vent stack" test. These two items are all part of one sequence test in the furnace upon start-up.
Again, the furnace already does this as part of the fire-up sequence. There's nothing to "check"; all the tech is going to do is watch the furnace run a full cycle. There's nothing "preventative" about this tech service. The furnace will fault out if the circuit isn't working. There is NOTHING he can "observe" in a "check" that would indicate a looming failure. The circuit either works or it doesn't. There is no "check" a tech will do other than sit and watch it work as it should. You can check continuity; who gives a crap? The fire-up sequence logic in the control board does this each and every time it gets a call for heat. If the circuit is close, it continues to go through the sequence. If the circuit is open, it sets a trouble code. There is NOTHING a tech can do during a "continuity check" that would prevent a future failure. The furnace will do that every heat cycle anyway.
Inspection would be looking for debris in the burners. This is very rare. It can be beneficial, but it's not really necessary. As for the burner, it's common for the tech to say "you have cracks in the heat exchanger; that's bad". But in reality, cracks are very common and most often a non-issue. Inspecting for these things typically leads to a tech recommending a replacement of something that doesn't need replacement. It is, at its core, a sales push tool.
Again, "verify" means watch it do its job. Or it doesn't, which would mean a service call is warranted. But a "maintenance" call does nothing to prevent this from failing in the future.
There's no adjustment to flames these days. Way back when, there were intake-air-slide adjustments that could be made. Not any longer; not for a long time now. The burners are fixed in their manufactured state. Observing them can only confirm a manufacturing defect; then a replacement would be warranted. If no defect, there's no need to "observe" this more than once. And in theory, the installer should have checked the initial operation. About the only thing that can affect the flame is to have an insect crawl into a burner and block the orifice or ceramic gas block; rare indeed.
Over and over, we're at the same point. Observing does nothing. The system either works or it doesn't. Observing the "normal operation" does not mean it will prevent a failure a month after the "inspection". Watching the blower ramp up/down today does not prevent a failure tomorrow. Observations do nothing. If the unit is malfunctioning at the current state, a service call is prudent. But a "preventative maintenance check" does zilch here.
Perhaps one of the few logical uses here. But this would be like the burner crack issues; the tech is likely to recommend replacement of perfectly operational caps just to cover his/her butt and also make a profitable sale.
This is of value in some circumstances, but not others. Not all discharge pipes need help, but some do.
Pretty much going to watch it run ... it works or not. If low on refrigerant, they'll top it off. End of story.
My point is that many of these "maintenance contracts" are very expensive, and yet provide very little ACTUAL, ACTIONABLE work. Most of it entails watching the unit run, and it's all good, and thank you for your $expensive annual maintenance payment. Plus, if something is verifiably wrong, they owner still has to pay for the labor and part for a fix, which would be no different than if the unit had an error or stopped and they had a "service call" rather than a "preventative maintenance call".
I worked at a major OE HVAC maker for 16 years, in the plant that made all the furnaces and fan coils, as a quality control engineer at first, then into other engineering assignments. For a time, I worked directly over the furnace and coil lines. I know them inside and out. I can tell you with certainty that MOST of the preventative checks you mention are bogus feel-good actions that have no bearing on how things run, and no true preventative value. Most (not all) of the items on your list are either useless, and those that aren't useless could easily be done by any homeowner after watching a YT video. Maintenance contracts are a big money maker for service entities; they are an insurance policy that you're going to be ripped off.
What I might agree with is that doing all those things you list perhaps once after the first 10 years, and then again every 5 years thereafter; that might be OK. But my objections are based on these "annual maintenance contracts" that have a fixed cost (typically $200-$400 annually) that do essentially nothing to prevent a failure. I am not saying doing some checks is not worthwhile. I'm saying the annual maintenance contracts have a very low ROI; typically, they just result in some part being replaced as a "preventative" measure when the part wasn't failing anytime soon.
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dn3: I think we are essentially on the same page...that maintenance contracts are unnecessary and expensive inspections that don't preclude the breakdown of HVAC equipment.
Other than cleaning the flame sensor and flushing the condensation drain line, there is nothing else being performed that is actually "preventive" maintenance. The only other potential maintenance item of value is if they wash out the debris buildup in the outside A/C unit's condenser coils. This cleaning provides a tangible increase in heat transfer ability of a heat pump and A/C system.
So based upon your insider knowledge of the HVAC industry, what brand and grade of HVAC system would you buy today? I am of the belief that simplicity equals reliability (e.g., 80% furnace and 15 SEER A/C, single stage systems are more reliable, albeit less energy efficient).
Other than cleaning the flame sensor and flushing the condensation drain line, there is nothing else being performed that is actually "preventive" maintenance. The only other potential maintenance item of value is if they wash out the debris buildup in the outside A/C unit's condenser coils. This cleaning provides a tangible increase in heat transfer ability of a heat pump and A/C system.
So based upon your insider knowledge of the HVAC industry, what brand and grade of HVAC system would you buy today? I am of the belief that simplicity equals reliability (e.g., 80% furnace and 15 SEER A/C, single stage systems are more reliable, albeit less energy efficient).
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dnewton3
Staff member
I, too, prefer the KISS method (keep is simple, stupid or keep is stupidly simple).
I believe the most simple system is a single stage non-condensing unit with PSC motors. PSC motors aren't efficient, but you can buy them cheap as replacements and they take no programming to run.
That said, I actually have a compromise in my house which I spec'd out. I have a single-stage condensing furnace and a single-stage outdoor condensing a/c unit. All have PSC motors. I gain some efficiency with the furnace condensing unit, but still have reasonable reliability. Condensing units have the secondary stage HX, and those are rarely ever a problem, as they don't see the bulk of the heat load; they essentially polish the product as it were. While there are issues occasionally with the condensate lines, it's not like you can eliminate those, because the a/c coils also use the same discharge line; any clogging issue would still be present. As for the outdoor condensing unit, I choose a mid-SEER product; they seem to represent a good balance between value and reliability.
I don't generally talk brands. Most of the major corporate entities make decent stuff. While I may be preferential to my old employer, I acknowledge that the major OEs all put out both good and bad designs. (Not unlike passenger vehicles). I always encourage anyone shopping for a new HVAC component or system to shop around; the dollars are what matter most. Don't get talked into up-market products; they are way more expensive and unless you live there for 20+ years, you'll never get the ROI, despite what the sales guy will tell you.
Most of the major OEs base their systems on tiered offerings, and the basic core of many systems use the same/similar components. Simply put, your money can buy efficiency, but it won't buy more reliability (with a few rare exceptions).
I believe the most simple system is a single stage non-condensing unit with PSC motors. PSC motors aren't efficient, but you can buy them cheap as replacements and they take no programming to run.
That said, I actually have a compromise in my house which I spec'd out. I have a single-stage condensing furnace and a single-stage outdoor condensing a/c unit. All have PSC motors. I gain some efficiency with the furnace condensing unit, but still have reasonable reliability. Condensing units have the secondary stage HX, and those are rarely ever a problem, as they don't see the bulk of the heat load; they essentially polish the product as it were. While there are issues occasionally with the condensate lines, it's not like you can eliminate those, because the a/c coils also use the same discharge line; any clogging issue would still be present. As for the outdoor condensing unit, I choose a mid-SEER product; they seem to represent a good balance between value and reliability.
I don't generally talk brands. Most of the major corporate entities make decent stuff. While I may be preferential to my old employer, I acknowledge that the major OEs all put out both good and bad designs. (Not unlike passenger vehicles). I always encourage anyone shopping for a new HVAC component or system to shop around; the dollars are what matter most. Don't get talked into up-market products; they are way more expensive and unless you live there for 20+ years, you'll never get the ROI, despite what the sales guy will tell you.
Most of the major OEs base their systems on tiered offerings, and the basic core of many systems use the same/similar components. Simply put, your money can buy efficiency, but it won't buy more reliability (with a few rare exceptions).
Missing on that list of preventative checks is actually measuring the start/run capacitors (they lose capacitance over time, from what I've heard) and measuring the gas pressure (the gas valve is adjustable) or using a combustion gas analyzer to check for proper combustion.
If this flame sensor is the same as mine I assume it's a thermocouple that produces something in the region of 30mV into the gas valve in order to latch it on. One test would be to measure the voltage output although you would need to know what it was when new. I don't understand the exact mechanism of why the voltage output deteriorates with age other than carboning up but it's hardly surprising that something might fail after being continuously sat red hot in a flame for years on end. I've had to replace mine only once after 20 years.
Prior to replacing it that one time I got it to keep working for a while by turning up the size of the pilot flame. In hind sight that was a serious false economy as I got to the point where the pilot light was using 4 KW of gas per day which at todays prices means I was spending £100 per year to heat a thermocouple that cost £3.50.
Even with a new thermocouple and the flame set to the minimum that will keep the gas valve latched it still uses £26 of gas per year. The cost of running the pilot flame is so much more than the cost of a new thermocouple that at any sign of a problem just replace the thing.
Prior to replacing it that one time I got it to keep working for a while by turning up the size of the pilot flame. In hind sight that was a serious false economy as I got to the point where the pilot light was using 4 KW of gas per day which at todays prices means I was spending £100 per year to heat a thermocouple that cost £3.50.
Even with a new thermocouple and the flame set to the minimum that will keep the gas valve latched it still uses £26 of gas per year. The cost of running the pilot flame is so much more than the cost of a new thermocouple that at any sign of a problem just replace the thing.
dnewton3
Staff member
This could be of value; that's true. But of the very few items which actually have some relevant use, would you want to pay $300 for a quick capacitor check and a condensate drain line cleaning? And whether that capacitor check actually gets done is of question; just because you may pay for it, doesn't mean it got done.
This would be an issue of gas supply (natural gas or propane). Once adjusted at installation, there should never be a need to readjust. If there's a supply line issue, you don't expect the furnace to compensate; you don't keep adjusting the gas valve - you go get the supply issue fixed.
This is pretty much moot today. Way back, when the burner flame was adjustable, then a gas analyzer was useful. Nowadays the furnaces are engineered to not be adjustable (mainly because too many people messed with the flame front and ended up causing safety issues in failed ignition and/or massive combustion issues). It is RARE that combustion is off from the factory; the fixed designs are pretty much spot on. Even if they were off, there's no ability to adjust them. So what good is a gas analyzer if you can't "fix" what is claimed to be wrong?
Things must be a lot different in England compared to the U.S. I don't recall seeing any gas furnace units for sale in the U.S. with standing gas pilot lights since the 1980's. I purchased my first home in 1980 and it had the spark ignition system which has been superseded by hot surface igniters for a couple of decades.
Some jurisdictions apparently REQUIRE a combustion analyzer test of a new system. I see Steven Lavimoniere using one every once in a while in his videos. https://www.youtube.com/@stevenlavimoniere
Also, it's not quite true that there's no adjustment--the gas valve IS adjustable. Incorrect adjustment of the gas valve would show up on the combustion analyzer.
How do you know if there's an issue of any kind if you never check?
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