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michael1 · Dec 29, 2008, 12:10 PM

We have a Janitrol Furnace, Model GMP075-3, Serial 9910624813 purchased in January 2000. It has not worked properly since it was installed. The problem seems to be the circuit board according to one of the service people. It ignites for 3-5 seconds and shuts off, lasts about 3-5 seconds and comes on again, burners come on, fan comes on, this keeps repeating with no heat being generated. This will be the third circuit board I have to replace, could it be something other than the circuit board.
Thank you

hvac1000 · Dec 29, 2008, 02:16 PM

Originally Posted by michael1

We have a Janitrol Furnace, Model GMP075-3, Serial 9910624813 purchased in January 2000. It has not worked properly since it was installed. The problem seems to be the circuit board according to one of the service people. It ignites for 3-5 seconds and shuts off, lasts about 3-5 seconds and comes on again, burners come on, fan comes on, this keeps repeating with no heat being generated. This will be the third circuit board I have to replace, could it be something other than the circuit board.
Thank you

Try cleaning the flame sensor. It will look something like this one.

hvac1000 · Jan 4, 2009, 05:19 AM

If you cleaned the flame sensor real good the it might be circuit board time again. That is a lot of circuit board replacements in 9 years so I would be looking at the power supply from the panel to the disconnect on the furnace and from there to the circuit board ESPECIALLY the ground wire which must be carried through from the house panel to the unit. A bad or defective ground can cause all kinds of problems with circuit boards.

hvac1000 · Jan 4, 2009, 05:22 AM

Also you will notice where the number 42 is pointing to. Sometimes these pins can become corroded and cause problems with the circuit board. Unplug and plug the connector in and out of the board 3 or 4 times to help clean the contacts. SEE image # 2

hvac1000 · Jan 4, 2009, 05:32 AM

On last thing you might try. Disconnect all the thermostat wires off the circuit board BUT write down EXACTLY where they came from. Then take a wire or jumper cable and jump the R and W terminals ONLY. Then turn the unit back on. If it runs OK then the problem is in your thermostat and not the circuit board.

MarkwithaK · Jan 4, 2009, 11:38 AM

OP, you seem bound and determined that your problem is in the control board and it very well may be. If you had a tech in to inspect it why didn't you have him complete the repair?

hvac1000 · Jan 4, 2009, 01:17 PM

If you had a tech in to inspect it why didn't you have him complete the repair?

Cause it is more fun trying to figure it out while driving us nuts. LOL

KC13 · Jan 4, 2009, 01:38 PM

It could be a defective pressure switch, even if the fault LED doesn't say so. Oxidized switch contacts can limit current and fool the circuit board while not supporting gas control operation.

michael1 · Jan 7, 2009, 10:26 AM

Originally Posted by hvac1000

If you cleaned the flame sensor real good the it might be circuit board time again. That is a lot of circuit board replacements in 9 years so I would be looking at the power supply from the panel to the disconnect on the furnace and from there to the circuit board ESPECIALLY the ground wire which must be carried through from the house panel to the unit. A bad or defective ground can cause all kinds of problems with circuit boards.

Thank you, I received the diagrams with numbers assigned to different parts, however, I do not have the log describing what the numbers are. Could you please provide that or if this was not meant for my question let me know that as well. Thank you

hvac1000 · Jan 7, 2009, 01:48 PM

I only provided the pictures to give you instructions on how the pin assembly/connector could have bad contacts. I sent pictures so it would be esaier for you to find the part I was talking about. I do not have a log for the pictures since the numbers are located in the master file and you only needed the picture of the circuit board that was being discussed as a possible source of your problem.