Builder installed Ventless Gas Fireplace in 2003. Operates by electrical switch. Does not always remain on after a minute or two. Must do a hard switch off/on to restart. May sometimes go off after an hour or two. I use it in the winter, from 3-6 hours. There is no apparent access to controls, and I have no manual. Can't even tell you the manufacturer. I believe problem may be in the switch, but that's too simple. What can I do now? Thanks.

Is the switch on or in the unit housing? If it is, it is quite possible that heat is affecting its performance. If the switch is remote on a wall somewhere where heat is not a factor, it is probably not the problem. Either way, it sounds like there is a loose connection in the wiring. If the gas valve is accessable, you could check the electrical connections. Most gas fireplaces opperate off of a millivolt system generated by the pilot light. There is either one or two devices heated by the pilot light which opperate the gas valve. It is also possible that one of them is producing marginal millivolts and this is usually caused by soot build up or the a weak pilot light. As you can tell, there are a multitude of potential causes. I would start with the swich and wiring.