York Diamond 90 - lockout caused by loss of flame

[gregr]

Each morning my furnace does the same thing...works properly once the thermostat calls for heat, but as soon as the furnace has run for about 45 minutes the heat stops, but the blower and venting motor continue to run. The board indicates "lock out caused by loss of flame" (8 flashes of the trouble light on control board). This only occurs in the morning, when the furnace is required to run for a longer period. I have set the thermostat to lower the heat at night by 2.5 degrees Celsius. I resolve the situation by resetting the system by shutting the power and turning it back on, at which time all works well immediately, until the next morning. This problem began a couple of weeks ago after I had had the original venting motor replaced, once it seized. I have removed all drainage hoses and cleaned them out, as well as the condensate trap. I have removed the flame sensor and cleaned it off with steel wool (it was only slightly dirty). I have removed all pressure switch hoses and verified that there are no blockages or water inside the switches (at least as far as I could see or check out with a gently inserted pin). Any help would be appreciated. Thanks, - Greg -

[Admin]

It sounds like a pressure switch problem.  The switch opens and closes so fast it interrupts ignition but then re-energizes the gas valve, which causes the flame loss lockout.

I bet whoever replaced the ventor forgot to remove the restrictor disc and install it in the replacement motor.  Let me know the model # of the furnace and I can give you a part number.  Or call the person who replaced the motor to see if they threw it out yet.  It's simple to remove the ventor motor and double check if the disc is there.

Keep your temperature on hold instead of lowering it at night until you resolve the problem.

Click Here to see the parts list for the York PS9 model.  Look at Item #41 on the parts break down, Combustion blower restrictor.

[acefurnacefixer]

Each morning my furnace does the same thing...works properly once the thermostat calls for heat, but as soon as the furnace has run for about 45 minutes the heat stops, but the blower and venting motor continue to run. The board indicates "lock out caused by loss of flame" (8 flashes of the trouble light on control board). This only occurs in the morning, when the furnace is required to run for a longer period. I have set the thermostat to lower the heat at night by 2.5 degrees Celsius. I resolve the situation by resetting the system by shutting the power and turning it back on, at which time all works well immediately, until the next morning. This problem began a couple of weeks ago after I had had the original venting motor replaced, once it seized. I have removed all drainage hoses and cleaned them out, as well as the condensate trap. I have removed the flame sensor and cleaned it off with steel wool (it was only slightly dirty). I have removed all pressure switch hoses and verified that there are no blockages or water inside the switches (at least as far as I could see or check out with a gently inserted pin). Any help would be appreciated. Thanks, - Greg -

I order to diagnose the issue, I would need to MEASURE the flame signal, as well as the draft that the ID motor is producing.If it is a flame sensor issue then I would ask if the furnace is properly grounded?

[gregr]

Thanks. Model number of my furnace is P3URD12N07501A. I happened to have kept the old ventor assembly, along with the repair part kit (``instructions indicate it`s inducer kit S1-32425960000 for use with models DGD, GDD, P2CDD, PBND, DGU, 6MG``).

Included in the parts box is the restrictor plate (AHA!) - a brown flat vinyl-type large washer-looking item. I suspect it`s the restrictor plate because the installation instructions included in the package refers to the brown restrictor plate (part S1-02815172000). Now my challenge is to verify if my model furnace is one of the ones in which this restrictor plate is required and if perhaps the contractor made an error in not installing it. The old venting motor assembly did not have a restrictor plate - the foam washer was still stuck in place - no restrictor plate beneath it. The instructions in the repair kit advise that ``Furnaces requiring the restrictor are as follows: DGD06010UA and B, GDD06010UB, P2CDD10N05701A, PBND-LD10N060``. I would assume that these refer to the model number, non of which match the model number on my furnace. Based on this do you think I can assume that this restrictor plate is not required and that the furnace contractor did the right thing by not installing it

I note that another part rattling around in the box is a black funnel-shaped reducer pipe (about 1 inch long) that fits neatly into the exhaust port of the old ventor assembly. The part is clearly not new - wonder if this has any significance

- Greg -

[acefurnacefixer]

Your best bet is have a qualified HVAC technician measure the draft that the draft motor is producing, also make sure that the condensate is draining properly.

[gregr]

Thanks all for advice. All of my efforts and research confirm the delicate balance of systems that needs to be maintained in these high efficiency furnaces. It's like a flashback to my youth and trying to troubleshoot an old 4 barrel holly carb - so many interconnected "systems" in place. Anyway, during my latest attempt at this tricky problem I was focusing in on the condensate trap. Mainly because it was the simplest (ie - not electronic) one to pursue. I was just about to remove it again and see if there was any blockages, when I tried blowing through the drain hose that carries the water from the furnace to a drain. This drain hose is semi-flexible and had been installed by previous owner (that's my disclaimer so that I'm never blamed for poor workmancship). I noticed that, as I blew on it, my breath did not flow unobstructed until I unblocked some water that was clearly sitting inside the hose. The initial resistance and the obvious sound of water being blown through the hose was the indication for me. I then discovered that there was a slight dip in the hose between support clamps (it was attached to the furnace wall along 2 sides with some clamps) and that this dip was just enough to allow a solid block of water to stand in it. I speculated that this may cause a slight backpressure situation which could possibly carry up into the condensate trap and further back into the rest of the system. So I reset and realigned the drain hose to provide consistent drain flow to the floor drain. Then I reset my thermostat to turn down  3 degress C at night (not my normal setback, but I wanted to go to an extreme for testing purposes). The result was no more problems with the furnace. So far.

[Admin]

Usually a drainage problem will cause a pressure switch lockout.  I guess time will tell.  Keep us posted!