I have a model R406A and getting the PV Output Fault msg. Three week prior to getting this message I replaced the LCD screen because it was unreadable. The cost of the PC board was unaffordable. Did I act prematurely and should have bit the bullet ($495) for the new PC board?
Maybe. The PV Output Fault message means that the system has detected an issue with power applied to the pilot valve when power should not be applied or vice-versa (no power applied when it should be).
You may have already done this, but powering the heater down completely (at the circuit breaker) for at least 2 minutes and turning the power on can force a reset of this error and, if it works, you are good to go. The heater sort-of does this on its own and will shut down for about 1 hour and then it tries to restart itself if heat is called for, but a good old-fashioned power reset may help.
If the error persists it indicates that 24 volt power may have been inadvertently wired directly to the gas valve (very doubtful for you since this is an established heater) or the valve relay on the circuit board failed and is stuck open or stuck closed.
I would do a couple of things before replacing the board: Start by inspecting it to be sure that, when the new LCD display was installed, something didn’t short out on the board. Look for anything, including pins from the LCD board that may not have been inserted properly or got bent upon installation or stray wires from the plug-in connectors.
If everything looks good and upon reinstallation you get the same error, remove the board again and tap the little rectangular black relay boxes a few times (hey, the board already isn’t working - I don’t think you’ll hurt it) to see if the relay pops back to its normal state and everything works again. If it does, you confirmed the source of the issue. It may work for a day, a month, or a year, but at least you will know that you may eventually need a new board.
Good luck, and let us know what you find!