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V12Tech
V12Tech, HVAC Technician
Category: HVAC
Satisfied Customers: 260
Experience:  A.A.S. MET, E.P.A cert, Certificate of Excellence HVAC/R
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Billy, weve resolved the grounding issue that caused the furnace

Customer Question

Billy, we've resolved the grounding issue that caused the furnace not to light, and I think I remember that everything was working OK at the end of last heating season. Now however, it behaves thusly: upon setting thermstat to heat and lowering the temperature setting below ambient, the ignighter succeds in lighting the main burner, which runs for about three seconds and then cuts out. The blower comes on and runs for a couple of minutes until it realizes the burner is not longer running and then shuts off. This whole cycle repeats periodically until I shut system off at thermostat. Any ideas? Thanks, Tim
Submitted: 1 year ago.
Category: HVAC
Expert:  Billy replied 1 year ago.

 

Hi Tim,

 

First lets cover the basics...

 

Have you cleaned the flame sensor with steel wool yet?

 

Billy

Customer: replied 1 year ago.


I'll try that, although you may not recall, the sensor is relatively new as I am pretty sure that is what we replaced to cure the flashing green light problem that brought me to you in the first place. I'll let you know.

Expert:  Billy replied 1 year ago.

Let me know after the cleaning what happens, code etc.

Billy

Customer: replied 1 year ago.


Billy, I finally got out and bought some steel wool. I carefully cleaned the flame sensor and tested the system. It seemed to run through one cycle without problem, but when I checked it again later it was doing the same thing. I really don't understand what's going on. Replacing the part resolved the problem of the twice-flashing green light and allowed the burner to run for longer than before, but not long enough to complete a cycle, and the part is relatively new with hardly any hours on it. What do you think is going on?

Expert:  Billy replied 1 year ago.
Do we still get a flashing 2 code?

Customer: replied 1 year ago.

when would I expect to see that? At what point in the cycle I described


?

Expert:  Billy replied 1 year ago.

IF there is a fault....which something other than the thermostat turned it off - a flash code should start.

It will then try to restart again.

Customer: replied 1 year ago.

I'll check it out tomorrow when it warms up.

Expert:  Billy replied 1 year ago.
Keep me posted.

Customer: replied 1 year ago.


Billy, I've been under the weather, but have finally managed to get down into the crawlspace to make the following observations. Upon calling for heat, the system responds normally, but about three seconds after ignition of the main burner, the flame indicator begins continuous flashing and several seconds later the burner cuts out. After an undetermined period of time, the process repeats itself. The really confusing part is that sometimes the burner does not cut out and the cycle completes normally. I haven't been able to discern any pattern to the failures.

Expert:  Billy replied 1 year ago.
Is the last burner at the sensor keeping reliable flame on the sensor or wavering?

Customer: replied 1 year ago.

Billy. This is getting really aggravating. I came downstairs this
morning to find that the furnace had been working properly all night.
Unfortunately, that is the exception. I have checked and the flame
sensor is centered in a very robust area of flame when the main burner
is running. Any ideas what is causing this erratic behavior? I have
checked the wiring and can't find anything loose. This has been
plaguing me for nearly a year. Please help!

Expert:  Billy replied 1 year ago.
When we took care of the ground...what was done to fix it at the time?

Customer: replied 1 year ago.

I installed a grounding rod and tied it to the cold water main and ran it to the retaining screw of the flame sensor.

Expert:  Billy replied 1 year ago.
Is that all still intact? Can you run a jumper from the falme sense mount to the ground of the circuit board? Even just an 18 g wire...

Customer: replied 1 year ago.


It's all intact. I sure thought we had this ground problem "run to ground." I'll see about this jumper business as well.


 


Thanks,


 


Tim

Expert:  Billy replied 1 year ago.
Keep me posted.

Customer: replied 1 year ago.


I have run ground wires EVERYWHERE, including stuffing one beside the pin of the green wire on the 9 pin plug inserted into the circuit board. i'm at my wit's end. To reiterate the behavior: call for heat, booster fan comes on, delay then igniter comes on, delay then burner comes on, delay of about 6 seconds and both the burner and the igniter turn off at the same time. At no time does the flame sensor light now come on.

Expert:  Billy replied 1 year ago.
The only thing left is to replace the circuit board assembly.

Everything else seems to be in place. The sensor is new/clean...the ground is in place.

It only leaves circuit board (which is the flame sense receiver).

I hat just replacing parts, but if there was ever a candidate, this one is it.

Billy

Customer: replied 1 year ago.


I guess you're forgetting that the circuit board is also new.

Expert:  Billy replied 1 year ago.
Yes I did.

But with proper ground we should have no issue

I will opt to the others for ideas

Customer: replied 1 year ago.

Please note that I am NO LONGER getting the flame sensor error light flash and that the burner and igniter seem to go out at the same instant.

Expert:  Billy replied 1 year ago.

Is there a chance the pressure switch is dropping out?

Is the code blink different?

Customer: replied 1 year ago.


There are NO blink codes of any color.


 


I don't know what the pressure switch is, nor how to determine if it is "dropping out."

Expert:  Billy replied 1 year ago.
What was your model number
Customer: replied 1 year ago.


Billy, I just returned from an out-of-town trip to find the house stifiling hot. Apparently, the furnace finally decided to respond to the 75 degree setting I had left it on during testing. This situation is so baffling. When I rhen reset the thermostat to a reasonable setting, it was back in it's old routine of cycling on for a few seconds only. Apparently it is capable of working properly sometimes, without any apparent change of conditions. Having replace the board, flame sensor, and gas valve, and grounded the hell out of everything, we're no further along with this. Did you ever get a chance to forward my problem to other experts?


 


Thanks,


 


Tim

Expert:  Rachel-Mod replied 1 year ago.

Hello,

I’m a moderator for this topic. It seems the Professional has left this conversation. This happens occasionally, and it's usually because the Professional thinks that someone else might be a better match for your question. I've been working hard to find a new Professional to assist you with your question, but sometimes finding the right Professional can take a little longer than expected.

I wonder whether you're ok with continuing to wait for an answer. If you are, please let me know and I will continue my search. If not, feel free to let me know and I will cancel this question for you.

Thank you!

Rachel

Customer: replied 1 year ago.


I would like an answer to my question, but I must insist that whoever takes over familiarize themselves with my previous communications on this problem as I've been struggling with this same question for SEVERAL months and do not want to cover ground I've already covered. If we can't get an answer sometime soon, I'm going to have to break down and bring in someone locally, and I don't want to have to do that.

Expert:  Rachel-Mod replied 1 year ago.

Thank you for your patience. We will continue the search for a Professional for you.

Rachel

Expert:  V12Tech replied 1 year ago.

This unit uses flame rectification,

this is a DC signal of micro amps that returns to the ignition module via the modules sense/ burner grnd terminal

. It transmits the weak DC signal to the module to prove a flame exists and is safe to continue operating

. I did not see if the port on the induced draft assembly, where the induced draft proving switch's tubing connects was reamed out good? It will obstruct and cause a wavering pressure thus pop open intermittently which is difficult to spot, I don't trust the flash codes myself, as there are only several possibilities to rectify this situation .

I have a routine I use for these ,

I clean the pilot assembly's mounting brackets surface areas and the burners surface areas touching the pilot assembly mounts, basically we are making a nice conductive path to home, being the burner grnd/sense terminal.

In addition I use 105C degree rated wire and connectors and run a ground wire in addition to the units grounding back to the terminal that is used for sense or burner grnd, usually they are common in the circuit board.

Remember it is only transmitting the faint DC signal that passes through the flame, a flame is a poor conductor and only transmits micro amps DC and that is easily stopped by a patina or moisture or corrosion etc, it does not take much and it is easily disrupted and restored. In fact many times new components seemingly rectify an issue, often the restoration of a ground path for the flame signal is really what fixed everything and if you try the old equipment, it is operative about 40% of the time according to manufacturers. Johnson controls makes a nifty flame simulator ($24)that simulates a nice DC signal that will work on any flame rectification system! it plugs in with the existing flame proving circuit and clamps to ground with a clip, If it wont run with this, no question the boards/module is defective, assuming all limits and safeties are closed, I often bypass them to test with them jumped to see what is going on..jumper clip the pressure switch once it has closed. For the pressure switches I use tattle tales to tell me if any control opens,even if a brief second, that is hard to spot unless gazing at it while it pops opens for 1 second , pressure switches on the threshold will waver and not be evident by watching , tattle tales have a flag that pops up if what it monitors trips or opens. You can by the and pressure switch for what a service call will be alone online and its very easy.Its not worth spending time troubleshooting parts that cost 10 minutes labor as in sensor and pressure switch and any auto reset limits. 1 yr of this is not worth this trouble, unlesss you had a $400 board i would sawp out the pressure switch, sensor limit and module, it wont be much online and if the pressure orifice is not clogged it will run no doubt with the system refurbished. I dont just replace a board and leave old cheap components there to fail next 6 months being a free call back and cutting my profits in 1/2. If a service tech is doing sub $300 service calls much he will be fired, go broke,etc. I had bosses tell me this in the early 90's.

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