gas furnance , i changed thermal culpling piolite light wont stay on

It sounds like you're having trouble with the pilot light on your gas furnace after changing the thermal coupling. Here are some steps you can take to troubleshoot the issue:

1. **Check the Thermocouple**: Ensure that the new thermocouple is properly installed and positioned in the pilot flame. If it's not in the flame, it won't generate enough voltage to keep the pilot light on.

2. **Clean the Pilot Assembly**: Dirt or debris in the pilot assembly can prevent the pilot from staying lit. Use a soft brush or compressed air to clean it out.

3. **Inspect Gas Supply**: Make sure the gas supply to the furnace is turned on and that there are no leaks. If you suspect a gas leak, turn off the gas immediately and contact a licensed professional.

4. **Ventilation**: Ensure that the furnace is properly ventilated. Poor ventilation can cause the pilot light to go out.

5. **Call a Professional**: If you’ve checked these items and the pilot light still won’t stay lit, it might be time to call a licensed HVAC technician. Typical service fees for diagnosing furnace issues can range from $75 to $150, depending on your location.

As a next step, I recommend getting 2-3 local quotes on Handyman.com to find a qualified HVAC professional.

— Assisted answer