Gas and Oil Home Heating Furnaces - Pilot is on but no heat

I have a Signature forced air heating system. Model:SRM54705A Serial:HX76NN3B3B3 3751. It is cold here.:D Ok Earlier in the year the pilot would not stay lit. So, I removed the pilot and pilot sensor(?) and thouroughly cleaned them. I vacumed everything I could reach and restarted the furnace.
2 months later. The pilot stays, but the furnace will not light. I have turned the thermostat all through it's range. I can turn the blower fan on manually. The gas water heater works fine and they share the same supply.
Thank you for any help you can offer.

Hello Hoorah. Welcome to the Heating and Cooling Appliance forum and the Do-It-Yourself Web Site.

Since you already replaced the thermocouple and the furnace continues to have the same problem, be sure the pilot flame is all blue, burning HOT, touching and encircling only the tip of the thermcouple. Be sure the thermocouple is snugly tightened into the magneto.

There must not be any yellow in the pilot flame. Yellow indicates the air hole in the pilot assembly is restricted with dust. If there is any yellow in the pilots flame, locate the intake air hole and clear or blow any dust or debris out.

Some of the other possible and or probable causes:
Assuming the firebox {Heat Exchanger} isn't cracked and or the flames aren't smothering, there is plenty of air supply around the unit for combustion air, the exhaust vent isn't restricted, etc. etc. etc.

Defective Gas Valve Solenoid:
The gas valves solenoid is internal.
Take the entire gas valve unit to your local appliance parts store and have the entire assembly and parts tested.

Defective Gas Valve:
Remove entire unit as an assembly. Take the entire assembly to your local appliance parts store for testing. Gas valves are not repairable. Replacement is the only option if defective.

CAUTION: Do Not attempt to repair the gas valve!
This is a non repairable item!

The Do-It-Yourself person can do some electrical tests and continuity tests on several electrical parts. However, I do not recommend relying solely on either test to determine if any electrical or electronic part or parts are causing the problem. The idea is not to replace costly parts until the defective one is found.

The only positive proof any part is functioning correctly, is to carefully remove the part or parts you suspect to be the potential problems, and have the local appliance parts store person test it or check it. Appliance parts dealers carry replacement parts for all appliances and are listed in the phone book under appliances.

Suggestions:
Read the manufacturers online web site for product information, problem solving methods, disassembly, reassembly methods, repair proceedures and instructions, pictorials and schematics, which may be available online.

Check the ARCHIVES, within this forum, for other postings on this topic and the replies offered.

Regards & Good Luck
Tom_Bart....TCB4U2B2B.....Company Enterprises
Fast.....Fair.....Friendly & Highly Efficient.....
Gas Appliances Forum Moderator
Energy Conservation Consultant & Natural Gas Appliance Problem Diagnostics Technician.

it is possible that a safety has been tripped preventing voltage from reaching the valve. a roll out switch or resettable high limit may be tripped. some may have a reset button, if possible, look for continuity across these devices. they will be wired in line with the gas valve.....just a thought

make sure you have moved gas valve knob to the on position---make sure it is not set to pilot position.PDF