Bryant Plus 90 Burners kicking on then off

[Burnin]

Hello, I have a Bryant Plus 90 398AAW048100D about 20 years old.

When the thermostat calls for heat, the inducer exhaust blower starts, shortly after the electronic pilot lights and burns for a while, a good while later (varying a minute to three or four) the gas valve will click and the burners will light. (I've read this should take 17 seconds from pilot light, but it is usaually much longer and varying in time).

Then the burners will burn out as if there was not enough gas. Then the burners will relight. This will cycle like this over and over with varying time between relighting.

Sometimes the gas valve will produce a click before relighting. Sometimes they seem to just relight without hearing a click.

I'm suspect of the gas valve itself for a couple reasons, but would like to get some feedback from an expert. If I lightly tap on the large selonoid on the gas valve, it will sometimes click, click, click, as I tap it. If the burners are running when I do this, they seem to vary in gas pressure and will flash some yellow flames. It also seems I can keep them running while continually tapping. Also, I noticed tonight that the large selonoid feels much hotter than the small selonoid and other components on the valve.

I have thoroughly checked all wire connections and everything it tight and connected.

I believe this is the valve in the system - EF32CW183 5-Wire Gas Valve

I have also read that a dirty or faulty flame sensor can cause similiar behavior. However, I'm not sure where that is to check. The only wires to the burner path are 3 to the electronic ignition /pilot assembly and the 4th high voltage wire. I'm sure it is part of the pilot assembly, but it is quite difficult to get at without disassembly.

Eventually and intermittently, the burners will seems to stay on and heat the house, only to repeat the behavior the next cycle.

With this description, is it logical to order a new gas valve and install, or would one recommend checking additional items.

Thanks

[HayZee518]

if you have a flame rod flame sense, this is integrated into the electronic ignition. there's a purge cycle for so many cycles before the control locks out. white - rogers makes a replacement ignition control with plug in cycle timers. your on-off cycle would indicate to me that the pilot keeps going out, then re-ignition starts. if you have a meter I'd connect it across the primary gas control solenoid and watch what it does when the main burner kicks in. if you lose the voltage while the burner fires, then I would suspect the flame sense electrode.

[Burnin]

Thank you for your response HayZee518.

Mostly, the pilot will stay on when this happens. Pilot lights, time passes, burners light and then burn out, pilot stays lit, as burners fire back up and then burn out again.

I do have a meter and tried to check control voltage, but wasn't sure which leads were the main selenoid. The gas valve has 5 connections labeled from back to front 5,1,4,2,3. I attached a picture of it I found. I checked voltage on 5 and 1 since that was closest to the selenoid, and I do seem to get a consistent 24-25 volts as burners are going on and off, and no voltage when everything is idle...but is that the right terminals?

I will try to dig into the pilot assembly tonight and clean it with a wire toothbrush or something....but what do you think?

Thanks

[HayZee518]

take a look at this site - it seems to be the most complete site for most hvac systems. you could even email them for their advice.
American HVAC Parts

[dw9663]

Burnin,

I am having exactly the same problem with my unit. Have you solved the problem yet and if so, what was the fix?

The direction I was heading was with the main board and the potential connection there, the feedback voltage to the lockout board from the tan wire (#4 on main connector I think) not reading voltage. But, I could be chasing the wrong thing for sure.

Thanks

[Burnin]

dw9663 - yes I solved the problem. It was not the gas valve. It was indeed the flame sensor. This is part of the pilot assembly, and my plumber buddy happened to have a pilot assembly that I put in to try.

You can indeed confirm it is the flame sensor with a meter. If I remember, you'll want to check at the termal furthest back and the one closed to you (I forget the numbers).

If it is the flame sensor / pilot assembly, you'll see 24 volt when the gas valve opens, and then at flame out, you'll see voltage go to zero.

In any case, if your shooting at it, I would shoot at this first and replace the pilot assembly.

Good luck.

[dw9663]

Burnin,

Thanks for the feedback. the one difference I realized is the last time the problem cropped up there was no response from the furnace. The tstat called for heat, but the furnace never responded. I was thinking it might be the lockout module and was wondering if anybody has any experience in this area. Does anybody know if it will reset if the power to the furnace is cycled? I can get the main blower to come on just by turning the fan on switch on the tstat, but it still does not start up the gas flame or appear to even try at this point.

Thanks

[Burnin]

I'm no furnace expert, but if you are getting no response at all then it could be many things. The first thing that should happen when the tstat calls for heat is the exhaust motor should kick on. If this isn't kicking on, then I am suspect of the relay board that starts this motor. (The older bryants have clear plastic relay's and the newer boards are solid state relays).

To test this, you can directly power the exhaust motor by unplugging it from the board and rig up a direct 110volt connection to the motor. (make sure the tstat is calling for heat also when you do this) When the motor starts and creates vacume in the combustion chamber, the furnace should cycle correctly to a fire up.

If this works, it is likely the relay board that energizes this motor needs changed (not the main board). Now, I know this because this did happen to me a few years ago. But I also learned that the wiring to the new board was a little different than the old board. To make a long story short, I also had to swap out the harness before I had it fixed.

In any case, if you can direct power the exhaust motor and get the furnace to work, you're on the right track.

[dw9663]

I am also not a furnace expert by any means. Turns out the lockout module quit allowing continuity. You can take it apart and clean the terminals so it gets good contact. I am guessing that going through multiple flame out cycles that it tarnishes the terminals and then fails. Cycling the power should restore functionality, but in this case it did not, but cleaning it worked. That board is also not that cheap, so it saves some money to try to clean it up.

I was down to replacing either the lockout module board or the main board (mine has the relays and thanks on the tip of different wiring if I ever have to change it) and it turns out the initial failure appears to be the flame sensor. In this case, it is the flame sensor, ignitor and pilot nozzle all in one.

Does anybody know which direction (cw or ccw) increases the pilot gas flow? Right now adjusting it either way does not change anything, so I am thinking there is a restriction in the nozzle of the flame sensor unit. The pilot gas flow adjuster screw is located on the main gas valve.

Thanks

[dw9663]

I changed the flame sense but teh problem still persists. The furnce cycles just as described in the very first post by burnin, and yes, eventually heats the house after several aborted start up cycles. The cycles are very consistent, to the point of the main burner firing up for about 5-10 seconds before a quick flame out, just as though it was shut off.

Any thoughts on this, I am thinking the main circuit board might need to be replaced, this one is the older relay style unit.

Thanks for any suggestions.