Bryant propane heater can't possibly be wired reversed (red LED blinks constantly)

I wouldn't bother. It's just going to get rusted again. The existing rust probably serves as a protective barrier. Remove it and you just expose more fresh metal to oxidize.

AC voltage and the flame lets the current flow in one direction only in ef fect creating a small DC current. The battery analogy is not exactly right .

Hi trader. yes I just learned this too, and it is interesting. Apparently the flame sensor circuits have evolved to this. I read that th e original flame sensors were just measuring the DC resistance through the flame, no flame is an open circuit, and a flame completes the circuit but w ith a high resistnace. The problem is that this is not fail safe. If the insulator that hold the flame sensor gets soot, that leakage resistance to ground can look like a flame. So if the insulator is sooty and the flame s hould go out, the controler would see the path through the soot and think t he flame is present. This of course is very dangerous. So they improved t he circuit, instead of just looking for DC resistnace, they found that a fl ame (unlike soot) conducts current in one direction better than the other. So the newer circuits apply an AC voltage, looks like a high impeandace an d pretty high voltage like 90V AC and the circuit senses that there is more current in one direction than the other. This indicates that there is an actual flame and not just leakage from soot.

So I'm guessing now that the 90 or so volts comes from the AC line and the controller circuit can't work right if the AC hot and neutral and ground ar e not connected correctly.

OP, what kind of VOM do you have. Not all can read MICRO amps. You would have to put the meter in series between the flame sensor and the controlle r. Unless you are good at this, I would not try it, you can cause damage.

Instead if you used an ohmeter to test the flame sensor by itself, connecti ng one lead to the flame sensor and the other to chassis ground, ___ IM GUE SSING__ you might see a resistance of 5 MEG Ohms (that is 5,000,000 Ohms not 5 Ohms) when the flame is present and if you reverse the ohm meter lead s the resistance should be a little lower in one direction than the other. And open circuit (infinity ohms) when no flame is present.

So the practical things to check are that all the ground connections are in place, that the AC supply polatity hot vs neutral is correct, that the fla me sensor insulator is not dirty, that the flame sensor probe itself is not very dirty and that the flame sensor probe is properly engulphed in the fl ame whatever that might be.

good luck

Mark

Often free with coupon and any purchase. I have several, and find them to be very useful.

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Wire brush, and blow the loose rust out. I've had case or two where rusty burner didn't light properly.

That could be your big problem.

I agree, if there is loose rust. From the pic I saw, it just looked like one end was rusty. If it;s just a light rust coating that isn't loose, I'd just leave it be. If you take it to bare metal, it's just going to repeat the rusting process.

The one I was remembering, there was enough rust that the flame didn't spread from one burner to the next. That might help explain the lockout, here.

Hi, Don't worry about the voltage out of transformer. It does not have tight specs. Can be as high as 32V AC. IIRC, the test runs the logic sequence up to the point of running normally. If some thing is not right it'll tell via error code. Did you see the HSI glowing to ignite? If so definitely next step is sensing flame by sensor, if not it'll quit and go into lock down mode but blower is still running to cool off. Then you have to power down and up to get out of lock down mode. If it has ground problem then clip one meter probe to furnace frame and probe all the [point on the board Ohmming it out to see any unusual high resistance at any point.

Hi, If you are stuck at this point then new sensor or board, only two choices, right? Being retired from Honeywell I can lean on guys still working there, electricians, process control technicians, etc. When I need parts I get help from them. On the control board there ought to be a chip(maybe op amp) which will convert that small amount of current to normal logic level(5V DC) to feed to ASIC(the brain of board) telling flame is on. One time there was a TSB out regarding one high Wattage resistor over heating causing solder joint to fail intermittent. I used tyo reinforce the solder joints and drill holes on the board cover near the resister for more cooling. If this resistor has poor solder joint, it will produce all kinda funnies.

They may have told you that, but I've never had a problem buying from them, and I'm not a contractor. It's close, just drive over. Then stop at the falafel drive-in across the street for a gyro & baklava.

scott

The COM terminal is used in conjunction with the RED terminal to provide power to 'smart' thermostats like the Nest or the Honeywell units that have Wifi radios and other circuitry that needs constant power.

---john.

trader_4 wrote, on Wed, 24 Dec 2014 04:13:39 -0800:

I have to agree with you.

One of the videos I watched was from a teacher who sabotages furnaces as a test for the students, & he said he can't make a flame sensor fail.

It's simply a stainless steel rod, mounted in an insulator, which is just about the simplest and most rugged of all possible sensors.

a. The rod can get carbonized (hence less conductive) b. The insulator could lose its insulating abilities (not likely) c. The burner can lose ground (or develop high resistance).

Even though I have a new flame sensor on order, I can't imagine that there is anything wrong with my current flame sensor, since, as you note, the thing is just a steel rod.

John Haskey wrote, on Wed, 24 Dec 2014 19:14:37 +0000:

In my case, the COM seems only to be used for the outside air conditioning unit.

trader_4 wrote, on Wed, 24 Dec 2014 04:04:51 -0800:

Fair enough. In my case, everything is working, so I guess that the "component test" didn't tell me anything.

The only problem is that the flame is incorrectly *not* being sensed, but the "component test" doesn't seem to turn on the flame, so, it wouldn't know that.

Tony Hwang wrote, on Wed, 24 Dec 2014 08:35:02 -0700:

Igniter works fine.

I borrowed a more sensitive meter from a neighbor, which can read down to 1/10 of a microamp.

It reads zero microamps when the flame is heating the flame sensor:

trader_4 wrote, on Wed, 24 Dec 2014 04:20:58 -0800:

Fair enough.

Since the flame lasts about 7 seconds, there was time just now to test the shutoff by shorting the flame sensor to ground within that seven second window. But, as you guessed, nothing different happened.

Tony Hwang wrote, on Wed, 24 Dec 2014 08:45:40 -0700:

I think I have three choices right now:

1. Bad flame sensor
2. Bad control board
3. Bad ground for the control board or flame sensor

I think the flame sensor being bad is really remote, only because the thing is simply a rod, and I've cleaned it with emery cloth to no avail.

The control board may be bad, but, it's certainly giving the flame sensor the nominal 90VAC that it's supposed to give it.

Here you see a reading of 104VAC from the flame sensor input wire to ground, which can only be coming from the control board.

Yet, when the flame sensor should be outputting 1ua to 6ua, it actually outputs nothing, even when tested with a sensitive meter:

I even grounded the burner with a jumper and nothing changed.

trader_4 wrote, on Wed, 24 Dec 2014 04:03:16 -0800:

I think my next step is cutting the control board out of its connection and looking specifically at the ground connections to the chassis.

trader_4 wrote, on Wed, 24 Dec 2014 04:23:53 -0800:

Too bad I had not seen this wise suggestion, as I did it already, and it failed to improve anything.

What I did was scratch off as much rust as I could with emery cloth and a file on the burner itself:

I even used Naval Jelley to remove some of the burner rust:

But, after scraping down to metal, & re-installing ... nothing changed:

I have nominally 90VAC (actually 102VAC) on the flame sensor, but,

Stormin Mormon wrote, on Wed, 24 Dec 2014 10:03:01 -0500:

I used a file and Naval Jelly and medium emery cloth to no avail.

In this picture, the right burner is the one I sanded:

It didn't make any difference, even when I added an additional black ground jumper from the burner metal to chassis ground: