Sounds like a Voltage Dependant Resistor, the 5 just indicates that it is the fifth one listed on the board.
I don’t know that board but looking at the images on connect it appears to be on the main power input (or very close to it) and I would guess that it is wired across line and neutral – the component is designed to act as a surge protector by only conducting above a certain voltage.
Are there any markings left on it or is it burnt to a crisp – photos of the board would also help so that I can check for certain how/where it is wired in.