Ruud silhouette II furnace

It sounds like there may be an issue with the ignition system of your RUUD Silhouette II UGLH-15EARJR furnace. Based on your description, it appears that the furnace is not always coming on correctly. The blower comes on, but after 30 seconds, you hear a click, and the far-right flame comes on, but it goes out after 5 seconds. Eventually, throughout the day, all the flames come on, but they don't come on the first time.
This problem could be caused by several issues, including a malfunctioning ignition system, a problem with the flame sensor, a dirty or clogged burner, or a problem with the gas valve.
To troubleshoot this issue, I would recommend checking the following:

• Check the flame sensor and make sure it's clean and properly aligned with the flame
• Check the burner and make sure it's clean and free of debris
• Check the gas valve, it could be stuck closed or malfunctioning
• Check the thermocouple, it could be faulty
• Check the control module, it could be malfunctioning

It's important to note that gas appliances are complex systems that require specialized knowledge and skills to troubleshoot and fix. If you are not comfortable working on these issues, it's best to call for professional help, as it may require specialized knowledge and skills to troubleshoot and fix the problem.

Right at the end of the pilot light.

Ruud Silhouette II Furnace Problem ' DIY Home Improvement Forum (diychatroom.com)

You will need the make and serial of you appliance from that you can get the part you need from a stockiest

Flame sensor needs to be cleaned. turn off the furnace power switch or breaker. pull the flame sensor located in the burner runner section of the furnace. It will be easy to locate because it has 1 wire running to it. pull the screw being very careful not to harm anything else. get the sensor out. inspect it for cleanliness. clean the sensor with light grade sand paper gently. re-install the sensor plug the wire back on. restart your furnace and this should fix the problem.
CookHVACR

Bad or dirty flame rod.
On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

Are all your supply vents open? The furnace may be oversized or have a air blockage. Have you always kept the filter changed. Newer heaters need the ducts sized right. If the new unit has worked great in the past then it's probally not the duct work.

disconnect the power. the flame rod is located at the end of the last burner. Gently remove it from its cradle and use a pencil eraser or a piece of scotch brite pad. If it doesnt allow the gas valve to stay opened after that, you should replace it

sounds like you have bad flame sensor or the sensor is in a bad postition. To get eliminate the lockout turn the power off to the unit and back on again. Look at the circuit board light and see what the troubleshooting code is.

it means that the flame sensor is not sensing a flame. If the flame is present and nice and blue the flame sensor is probaly dirty. Remove the flame sensor and lighty sand it with sandpaper.