Gas Firplace fog

Today at an inspection (sealed unit, direct vent, switch activated) I activated the gas fireplace via wall switch, first, I heard a clicking sound, pilot I figure, secondly the glass fogged up on the inside, white milky, from what I understand this is a sulfuric acid type substance related to moisture, I had before hand inspected and tested the AC so it was pretty cool inside, when I shut down the fireplace via wall switch it once again made the clicking sound, it seems to be in some type of service mode,I tried to adjust using the control module, (behind the drop grill) but the batteries were missing, I do not want to recommend a gas fireplace tech because from what I understand the fogging does happen, but the clicking sound I do not understand, I think if the batteries were in the built in module I could have gotten it out of this mode, any help will be appreciated, the house is 2 years old and I may have been the first to activate the fireplace, wouldn’t be the first time, any help will be appreciated, thank you in advance.

Fogging of glass is most likely from the normal combustion of gas which are heat plus CO2 and water. The glass will fog until it has warmed up. Takes about a minute or so.

Clicking noise may have been igniter, but there would also be the forced draft fan that draws combustion air in from outside and expels the exhaust gas out of the direct vent.

This fan will shut down some time after the unit has been switched off, it is an automatic control designed to shut down after all products of combustion have been cleared, and the unit has cooled off.

I am not sure what the control module would need batteries for - was there no line power? I have seen remote controls for gas fireplace, but they were not necessary to operate the unit.

You don’t say whether the fireplace actually worked as it was supposed to, that is produced a flame and heat, if it did and it shut down properly it sounds like it was working properly.

Batteries are for a remote control, fogging is normal it will clear

I don’t recommend mentioning “sulphuric acid” to the client - like Eric said, products of natural gas combustion are mostly CO2 and water.

“Fireplace did not operate as intended during inspection. Recommend having a qualified fireplace contractor evaluate and repair if necessary”

Also, we were just in a gas fireplace store and the tech told us that batteries can be used in place of a pilot light (with electronic ignition) to light the fireplace in the event of a power outage.

Yes i forgot that one too

Thanks all, I just got back to the forum, report was sent yesterday with a recommendation for gas fireplace service, The water heater, furnace, and AC had never been serviced, so I added on the Gas fireplace, and yes from what I understand the milky substance forms on start up then goes away but this did not, got worse, I figured the clicking was igniter but why was it clicking on shut down, and yes on some models there is a control module behind the grill (battery operated) in case of power failure, this is where the batteries were missing, anyways coming across this problem gave me a chance to research and learn some new things, thanks for the replies.