Furnace issue, will not start on it's own.

Kisskrazed · 11-30-2011, 11:26 AM

First off, WOW what a forum with such great info, I have learned a ton reading up on issues that have been solved that I have had problems with in the past on various projects.

My furnace is another matter, It's not my cup of tea at all. Older house with older furnace. (I can get model number if needed) On the attached picture, I have to "tap" this area on the gas valve, to assume this enables the gas to flow to electronic igniter & the furnace to come on. (Gas valve model is 36C84 type 201)
Thermostat (also older model) is set to come on at a certain temp. but the furnace does not. It will shut off at the desired temp. but will not come on by itself unless "tapped" as in the picture. Also, sometimes if the thermoset is set really low, & it is raised, the furnace will come on but that is few and far between.
Any ideas? Calling our local HVAC Co. is not a option currently $$$. Thanks in advance for your suggestions.

harleyrider · 11-30-2011, 11:33 AM

Quote:

Originally Posted by Kisskrazed

First off, WOW what a forum with such great info, I have learned a ton reading up on issues that have been solved that I have had problems with in the past on various projects.

My furnace is another matter, It's not my cup of tea at all. Older house with older furnace. (I can get model number if needed) On the attached picture, I have to "tap" this area on the gas valve, to assume this enables the gas to flow to electronic igniter & the furnace to come on. (Gas valve model is 36C84 type 201)
Thermostat (also older model) is set to come on at a certain temp. but the furnace does not. It will shut off at the desired temp. but will not come on by itself unless "tapped" as in the picture. Also, sometimes if the thermoset is set really low, & it is raised, the furnace will come on but that is few and far between.
Any ideas? Calling our local HVAC Co. is not a option currently $$$. Thanks in advance for your suggestions.

Thats a mercury switch, I have never been fond of them at all. Try cleaning the pilot and orifice to improve flame contact with business end of that mercury switch. You can see a large gap between the valve and the receiver on the switch....... push that back in and possibly put a wire tie on it?

Kisskrazed · 11-30-2011, 11:59 AM

Thanks for your reply. So are you also thinking that it's most likely the gas valve or a contact rather than the thermostat? The gap is interesting, I can move the box (with arrow) front and back as it is facing in the image to some degree, but I do not believe in will go right or left (toward the other box)

how · 11-30-2011, 12:14 PM

Mercury sensor systems are troublesome. A partially obstructed pilot orifice is usually the starting point in helping this system work. Try knocking on the pilot assembly with a large screwdriver like you'd knock on a front door. What you are trying to do is dislodge any debris at the pilot orifice so that the pilot gas pressure will push it aside. Watch each time to see if the pilot flame increases in size. If it does increase in size, stop and see after a minute if the system now works. Do not knock the mercury sensor in the pilot flame or your repairs will get a lot more complex.
Harleyrider gives the right info but I find dissembling pilot orifices is sometimes more than a DIY wants to try.

Kisskrazed · 12-01-2011, 11:02 AM

No luck with what was suggested. i'm going to see if I can find one here locally without breaking the bank. Time for a major upgrade in the spring I believe.