York Gas Furnace model 9.S four red flashes

[Rolland]

I have a 6 yr old York gas furnace model 9.S. I worked well for the first 3 years. Then it started cutting out after giving heat for a while. It works when I turn it on then the flame goes out and the LED flashes red four times indicating an open limit switch. When it's really cold outside and the thermostat is asking for 75 degrees it will sometimes stop at 65, the blower fan will keep running then it will cycle back with some heat on it's own then off again with the four red flashes when there is no flame and the temperature has not been reached.

I disconnected the limit switch on the top left just below the burner and above the vacuum switch and shorted the two wires together to confirm that the switch was the problem. I thought the heat would then stay on until the thermostat temperature was reached. To my surprise after a little while the four beeps came back and the flame went out. Is there more than one high limit switch on this furnace? What else could be causing this?

Thanks.

[paul52446m]

I have a 6 yr old York gas furnace model 9.S. I worked well for the first 3 years. Then it started cutting out after giving heat for a while. It works when I turn it on then the flame goes out and the LED flashes red four times indicating an open limit switch. When it's really cold outside and the thermostat is asking for 75 degrees it will sometimes stop at 65, the blower fan will keep running then it will cycle back with some heat on it's own then off again with the four red flashes when there is no flame and the temperature has not been reached.

I disconnected the limit switch on the top left just below the burner and above the vacuum switch and shorted the two wires together to confirm that the switch was the problem. I thought the heat would then stay on until the thermostat temperature was reached. To my surprise after a little while the four beeps came back and the flame went out. Is there more than one high limit switch on this furnace? What else could be causing this?

Thanks.

is this a down flow furnace? return air comes in the top and hot air out the bottom? Is this a 90+ furnace? When you say it might stop at 65 when set at
70 , do you know is the stat stop it or is it still calling for heat? what stat do you have? Paul

[Rolland]

Hi. Thanks for your reply. This is not a downflow furnace. The cold air return is at the bottom and the heat comes out of the top. I don't know the actual efficiency of the furnace. It is a York Affinity 9.S model. Since I posted my question I looked around the furnace and found that there is a limit switch in the inducer motor which is in series with the main limit switch. The inducer motor was replaced twice already because the plastic blower wheel had disintegrated each time. I suspect that the inducer motor runs too hot. It is very hot to the touch and the limit switch in it is probably causing the furnace to stop even though the thermostat is still calling for heat. I wonder what could be the cause of the inducer motor running so hot. Could it be a poor design? Not enough air flow out of the furnace? Or the combustion air intake being partially blocked by a dead bird in the pipe or something?

[paul52446m]

Hi. Thanks for your reply. This is not a downflow furnace. The cold air return is at the bottom and the heat comes out of the top. I don't know the actual efficiency of the furnace. It is a York Affinity 9.S model. Since I posted my question I looked around the furnace and found that there is a limit switch in the inducer motor which is in series with the main limit switch. The inducer motor was replaced twice already because the plastic blower wheel had disintegrated each time. I suspect that the inducer motor runs too hot. It is very hot to the touch and the limit switch in it is probably causing the furnace to stop even though the thermostat is still calling for heat. I wonder what could be the cause of the inducer motor running so hot. Could it be a poor design? Not enough air flow out of the furnace? Or the combustion air intake being partially blocked by a dead bird in the pipe or something?

Ok you do need to check your stack and intake to make sure they are clear.Check your book to make sure they do not have too many ell or too long of stack runs. Make sure stack has not got too hot and started sagging between hangers, so it would be holding water. When the furnace stops check all drains to make sure they are not holding water back. Is this a LP or Nat gas furnace ? Gas valves can slip and start passing too much gas and that would over fire the furnace and run the inducer too hot. If you furnace is nat. gas your furnace book might tell and show you how to clock the meter to make sure it is firing at the right BTU. Is there a drain switch in that limit circuit? . Paul

[SeattlePioneer]

Interesting... I don't recall seeing a furnace that has a limit switch at the inducer motor assembly. Most inducer motors have a thermal limit which shuts off the motor if the motor overheats, which is what you appear to be describing. When that happens the pressure switch would typically open and shut off the burners. Sometimes an inducer motor has a small fan next to the motor to circulate air across the motor and keep it cool. I wonder if that fan may not have been reinstalled when you had repairs made. In addition to things suggested by Paul, I'd pull the inducer motor assembly and check the condition of the fan for plugging or deteriorated fan blades, and especially to try turning the fan to see if it is stiff and hard to turn, which would place an added load on the motor and could cause it to overheat because of failed bearings.