Paloma Tankless Water Heater error!

[biffer]

I have a Paloma Tankless Water Heater and after 2 years with no problems, I am now getting a C2 11 error code when I call for hot water. I have checked to make sure that the water and gas valves are open, and all the basics. I'm hoping there is just a sensor that needs replaced because it seems like the flame is good it's just that the sensor isn't long enough time before it shuts down and tries again. I can turn the hot water on and I'll get the error code, so I leave the water on and go to the heater, then I can feather the hot water outlet valve and get it to work correctly. So I'm hoping it's something simple.