Gas fireplaces/mercury flame sensors


Old 02-18-19, 07:10 PM
Thread Starter
Join Date: Feb 2019
Location: United States
Posts: 3
Received 0 Votes on 0 Posts
Gas fireplaces/mercury flame sensors

Do some older gas fireplaces have mercury flame sensors? If so, how do you distinguish between a mercury sensor and a thermocouple or thermopile? (See attached photos) Do the mercury sensors break easily?

Name:  fp1.jpg
Views: 78
Size:  113.3 KB

Name:  fp2.jpg
Views: 79
Size:  119.9 KB

Last edited by PJmax; 02-19-19 at 07:25 PM. Reason: cropped/resized pictures
Sponsored Links
Old 02-18-19, 07:24 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 59,794
Received 1,193 Votes on 1,104 Posts
If it is a standing pilot light....... not intermittent ignition...... then it will be a thermocouple...... not a mercury flame sensor.

I've never come across a mercury flame sensor in a fireplace. The mercury is contained within a metal tube but I guess that tube could be burned open.
Old 02-19-19, 04:35 AM
Join Date: Jan 2017
Location: USA
Posts: 541
Received 5 Votes on 5 Posts
When I got into the residential heat & A/C service 50 years ago (wow ,how time flies) this type of pilot safety control was common. The nice thing about this device was that it would reset itself after the pilot was re-lit without having to push a reset button or switch. They can still be purchased. The ones I used were made by White Rodgers. There is no way that I know of as to know when they will fail. They just quit working. Mercury sensors look like a thermocouple but the end that usually has a thread has a a box that is permanently attached to the thermocouple and the box has terminals for wiring. A thermopile has 2 wires on the end to connect to a device or gas valve. They used to come as 2 types; a fat pencil type or a flat wafer type. I do not think that the wafer type is made any more. hope this helps
Old 02-19-19, 07:28 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 59,794
Received 1,193 Votes on 1,104 Posts
When I looked again at your pictures..... what you have appear to be log lighter burners. You light them with a match and then they get the logs started. If those are ceramic logs.... then they are just basic burners you light with a match. I don't see any flame monitoring equipment in use.
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title: