Common furnace repair - fixed, but worth a read - Page 1
Forum section: electronics / repair

author: cncjerry
author_rank: Unknown
timestamp: November 01, 2017, 12:47:47 am
content: So my wife said, "do something about the furnace coming on every night." I replied, "I'll turn it down" and she said, "no, because then it will be too cold in the morning." I said, "I'll program it" and she again thought this was a bad idea because then she might be cold at night. The furnace runs pretty much every night because in San Francisco it is almost always cool in the early hours, plus she sleeps with the windows open. After explaining about having the cake and eating it too, she told me to turn it off for the summer, which I did, for the past 4 months. Finally had an electric bill under $250. I wonder at this point if turning it off for that period of time contributed to the failure below?Anyway, it starts to get cooler around now so I turned it on and of course, no heat. Most of these furnaces are the same or follow the same initialization cycle. Mine was getting to the point where it cycled the larger fan and the smaller fan to evacuate the gas combustion area, turned on the electric glow plug and then should have tripped the gas valve. At that point it didn't and presented a blinking error code 21. This means something like "the fire didn't ignite" but it is more cryptic as it really means that either the gas is off (you didn't pay the bill), the CPU is not working, the igniter wasn't working or the gas valve didn't open; basically the furnace expected a gas fire and never detected one.After checking all the sensors, I found I had no voltage to the gas valve itself. The most interesting sensor is the "flame rollout sensor" which detects the length of the flame in the combustion chamber. After another argument with my wife about not touching the thermostat while I am up to my elbows in the furnace surrounded by 6 blow torches and a fan that could give a wood-chipper a run for its money, I found that yes, indeed, no voltage to the gas valve. In her defense, she argued that she didn't want cold air blowing on her at night even though I was at risk of life or limb. I explained unsuccessfully that the cold air was only during the time I was testing but of course, that wasn't a good enough excuse and I slept in my sons room.I finally decided that the gas valve relay on the CPU motherboard wasn't being tripped and when I opened the board up, I found two cheapo brown caps, both 47uf and 63V had pissed all over the place. I suspect had I called the service man (or allowed the one my wife called while I was at work today) to come over, he would have replaced the motherboard at a cost of $350 for the board, $150 for the initial diagnosis and $250 for installation labor.The final thought here is that I often find I don't apply my electronic skills liberally across all areas. Furnaces have always sort of spooked me because of the 220V, gas, heat, etc. Not that long ago I had an A/C fan short to the motor frame. It was really hot, I was sweating like crazy, took a shower and thought, what the heck, maybe the fan isn't starting because of a starter cap, let's give it a spin (fresh out of the shower, naked, covered in water. I woke up on the floor with a large cut on my arm where I yanked it out of the box fan when I was nearly electrocuted by leaning on the grounded frame while spinning the live inner blade of the fan. Someone told me older A/C unit fans are electrically isolated using rubber grommets on the motor. In this case, the fan motor shorted to its frame and then I touched it as well as the grounded A/C ventilation generating the NDE.Anyway, all is well, my wife is happy with the heat and I have $350 + $150 + $250 = $750 I shouldn't have, so what to buy, what to buy?Jerry

author: texaspyro
author_rank: Super Contributor
timestamp: November 01, 2017, 12:55:36 am
content: Quote from: cncjerry on November 01, 2017, 12:47:47 amEasy... a consultation with a divorce lawyer. Them wifey thingies are rather expensive to keep around and maintain.

author: helius
author_rank: Super Contributor
timestamp: November 01, 2017, 12:58:39 am
content: You never go to sleep with the gas on. Isn't that common sense and self preservation?

author: rrinker
author_rank: Super Contributor
timestamp: November 01, 2017, 01:27:45 am
content: Mine did that the first year I moved in here. And it wasn't a very old furnace, only a couple of years old. Code said the flame sensor failed. I was close to ordering one but then - I don't like fooling around with gas, so I called a professional. He replaced the flame sensor. Wasn't really any more expensive than me buying the part and doing it myself, since it was covered under the home warranty provided by the previous owners. If the same thing happens, I'll do it myself now because I know the exact part number required and the exact process (10 minutes) to change it out.

author: Ian.M
author_rank: Super Contributor
timestamp: November 01, 2017, 01:37:14 am
content: Quote from: cncjerry on November 01, 2017, 12:47:47 amA lockout-tagout kit for your breaker panel, and an insurance policy that will pay for a full forensic investigation in the event of your untimely demise, even if the police don't think one is necessary, and a codicil to your will that states your wife doesn't get a cent more than a basic cost of living allowance till the forensic investigation has proved your death wasn't suspicious or due to her negligence.

author: wraper
author_rank: Unknown
timestamp: November 01, 2017, 01:39:39 am
content: Quote from: cncjerry on November 01, 2017, 12:47:47 am. Wasting energy right down the drain.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 01, 2017, 02:07:12 am
content: Flame sensors of the kind that are in my furnace are a simple metal rod in a ceramic insulator with a single push-on terminal. The only magic part is that the rod is made of some special blend of "eleven herbs and spices"* The principle is "flame rectification". Apparently the controller board applies some AC signal to the sensor and detects whether the flame is rectifying some portion of the current and shorting it to ground.Apparently the primary failure mode for these things is that an insulating layer gets deposited on the surface of the rod over time. Cleaning the rod (with steel wool) apparently fixes many/most failures. It got my furnace back running again.Ref:https://en.wikipedia.org/wiki/Flame_rectification* Ref: AvE

author: cncjerry
author_rank: Unknown
timestamp: November 01, 2017, 03:37:15 am
content: Quote from: Richard Crowley on November 01, 2017, 02:07:12 amMy brother mentioned something about flame rectification for the sensor. I wonder how that actually works?I wonder how many of those CPU motherboards were pitched because of two faulty caps? It was weird how the cap fluid migrated as well. It sort of went horizontally and then up instead of just dripping down with gravity.

author: jmelson
author_rank: Super Contributor
timestamp: November 01, 2017, 08:42:42 pm
content: Quote from: cncjerry on November 01, 2017, 03:37:15 amYeah, I've been babying a fancy energy-saving washing machine with an insanely complicated controller board. It has about 12 mechanical relays and a VFD for the permanent magnet AC motor. I replaced the most-often cycled relay with a solid state relay, and have had to hack a few other things on it. I would have paid $350 multiple times with this thing if I hadn't been working on it myself.But, the FINAL problem determination is there are some flow restricting rubber washers in the valve assembly that slow down the water filling the tub. These are hidden behind the debris screens where you connect the supply hoses. Well, apparently, these washers swell over time and restrict the flow to a dribble. Then, the tub takes too long to fill, and the machine stops filling with an error code. I eventually took the washers OUT, and the machine runs fine! Who designs this stuff? Or, worse, who decides they don't need to TEST anything?Jon

author: cncjerry
author_rank: Unknown
timestamp: November 01, 2017, 09:19:10 pm
content: you know, it sounds sort of like my prostate.

author: Samogon
author_rank: Frequent Contributor
timestamp: November 01, 2017, 09:24:45 pm
content: Quote from: jmelson on November 01, 2017, 08:42:42 pmBe grateful to Gov, there is some code forcing manufacturers to put water saving rubber washers on all shower heads, faucets, probably appliances too.I read it on the user manual for new shower head i installed.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 01, 2017, 09:37:35 pm
content: How does simply filling the machine SLOWER actually "save" any water? The machine reacts to the VOLUME (weight) of the water, not how fast (or slow) it took to fill.The reason for restrictors on shower-heads (etc.) depends on users getting bored trying to shower under a piddly stream, giving up, and getting on with their day.Washing machines don't get bored. But they may throw an error if they think it is taking too long to fill (as with the clogging restrictor washer).That is actually a GOOD thing. If there were a leak in the drum and the water was running all over your floor, you wouldn't it want to continue running forever.

author: Electro Detective
author_rank: Super Contributor
timestamp: November 01, 2017, 10:07:39 pm
content: Quote from: Samogon on November 01, 2017, 09:24:45 pmSlightly OT:Those crappy rubber washers aren't doing anyone any favors after a couple of years useThey degrade badly and the unaware consumer drinks the deteriorating black crap and breathes in the rubber vapors during a hot shower etcPull one of these washers out and gently rub it and see the black crap melt and stick to you.. free finger dyeWhen these rubber washers eventually go south BADLY, they are a pain to remove if stuck inside a fixtureNeedless to say, I've had my fill of them over the years and replaced the lot (even on new stuff) with non rubber equivalents'Gov' needs to do some HOMEWORK first, then enforce codes on manufacturers that are not halfassed 'water saving' consumer solutions

author: cncjerry
author_rank: Unknown
timestamp: November 01, 2017, 11:16:59 pm
content: Here in California we have these low flush toilets that have what seem to be narrow drain tubes, probably to make sure the neck stays full to prevent gas coming up. But I guess the person that spec'ed them never thought how many times you have to flush the darn thing during a typical dump. I doubt very much they are saving water on these things.I Have a friend that to this day, and he started back in the 80's, travels with a set of wrenches to take the flow restrictors out of the showers in hotels. Now there's dedication.Jerry

author: Zucca
author_rank: Unknown
timestamp: November 02, 2017, 09:41:20 am
content: Hi Jerry!Quote from: cncjerry on November 01, 2017, 12:47:47 amAnd you with the windows closed?Quote from: cncjerry on November 01, 2017, 12:47:47 amIf someone doesn´t get that after 30 sec. discussion I give up and declass him/HER to below dolphin intelligence.Quote from: cncjerry on November 01, 2017, 12:47:47 amHere in Europe is the same but with 380V.Quote from: cncjerry on November 01, 2017, 12:47:47 amCarpenters says check twice and cut once.EE says measure twice and touch once.Quote from: cncjerry on November 01, 2017, 12:47:47 aman air to air heat exchanger device... and close that damn window at night.https://en.wikipedia.org/wiki/Heat_recovery_ventilationbut your wife needs to understand that from that device is coming fresh air out, even if the windows is closed.You can prove it will save $ every month because the heat energy is not pissed away in the San Francisco sky, and you could buy whaever you want every months.

author: Electro Detective
author_rank: Super Contributor
timestamp: November 02, 2017, 09:49:17 am
content: If it's that cold and you need fresh air and lower bill$, wear socks in bed and a scarf, works greator get some nookie action in, to raise the temperature

author: CJay
author_rank: Super Contributor
timestamp: November 02, 2017, 10:42:40 am
content: Quote from: zucca on November 02, 2017, 09:41:20 amIf a carpenter gets it wrong then he needs a replacement piece of wood, if an EE gets it wrong then you need the carpenter to build the box for the old EE and a replacement EE

author: Samogon
author_rank: Frequent Contributor
timestamp: November 02, 2017, 01:13:56 pm
content: Some EE lacks humor sense.

author: cncjerry
author_rank: Unknown
timestamp: November 02, 2017, 04:53:38 pm
content: QuoteI moved into another bedroom after the kids left. If I can figure out how to get gas into the other bedroom I will move to phase 2 of the plan and have my own kitchen as well.Furnace repair now has a few days on it and it is running great. I've replaced a bunch of those little nichicon caps over the years and glad I found the leak. Come to think of it, it would be nice if caps leaked in a specific color based on brand. It would make it easier to find.

author: jmelson
author_rank: Super Contributor
timestamp: November 02, 2017, 05:20:22 pm
content: Quote from: Samogon on November 01, 2017, 09:24:45 pmBut, on a washing machine, it fills until the level sensor says that is enough, so it will NOT save any water. What it DID was make it take over 45 minutes to fill the tub, EACH FILL! That extended a 50 minute wash cycle to a 3 hour wash cycle, **IF** you watched it like a hawk to keep resetting it when it stopped with the dreaded "LF" error code (means long fill).Groan!!Jon

author: Towger
author_rank: Super Contributor
timestamp: November 02, 2017, 06:42:10 pm
content: There is nothing like sitting at the kitchen table covered with the guts of your heating system, with a hot soldering iron on a cold Sunday morning.

author: Seekonk
author_rank: Super Contributor
timestamp: November 02, 2017, 07:14:41 pm
content: I just fixed my furnace which is 20 years old. Last year the thermostat display would go out now and then. The outer section of the thermostat just snaps into the mounting plate and connects with a 16 pin header. When It would die, I would just snap it off the plate and then plug it back in. That always seemed to work.This year it didn't. I checked the voltage at the terminals and it was 13VAC. Isn't that supposed to be 24? Went to the basement and the transformer put out 24V. Noe the wire leading up to the thermostat read 0V. Everything is in wire bundles so I actually dug out the manual for the schematic, this is taped to the side of the furnace. There is a high temp limit switch that interrupts the power and it wasn't making it through. Pulled it out and it is a common round snap disk. Wiggled all the connections and it seemed to work after that. Wife yesterday said the display was gone. Wiggled those connections again and it worked. I'll replace it some day, got that part somewhere. Perfect example of how contacts oxidize and fail with low voltage.Professionals........ My neighbor just converted from propane to natural gas. There was this service truck at the house for five days. Couldn't figure how it could take so long. Finally they are connected and go away for a day trip. Next day he says, did you see all the commotion at 11 last night? We came home and the house was filled with gas. At least they didn't evacuate me! This guy who tool forever didn't tighten a pipe enough. Professionals, what a bunch of crap. They hire the cheapest people they can get.

author: jmelson
author_rank: Super Contributor
timestamp: November 03, 2017, 09:34:48 pm
content: Quote from: Seekonk on November 02, 2017, 07:14:41 pmWHOA!! Lucky the whole neighborhood didn't get blown up! Fill the house with gas, and either the water heater or the furnace will eventually light it off, and the neighbors get their house shifted off the foundation.Jon