Old Silver-Line furnace problem

avro1 · 11-29-2009, 04:38 PM

I just found this site a few days ago and I'm quite impressed at all the knowledge here! That said, I'm hoping some of you can help me out...

I have this OLD Silver-Line gas furnace that was made in Winnipeg, Manitoba at least 40 years ago(has a service sticker on it from 1969). I've owned this house about 8 years and the furnace has worked flawlessly until about two years ago when the burner wouldn't light. I cleaned the wire splice(they were just twisted together) between the thermostat wires and the wires to the furnace and it fixed the problem until last spring when it happened again. I cleaned them and this time used a crimp connector for a "permantent fix" which worked until last week but now the burner won't light again. Actually the burner does light and stay on IF I jump the thermostat terminals on the gas valve OR touch my two crimp connectors together but not if I jump the wires up at the thermostat....odd.

I believe the furnace uses a millivolt gas system because it only has two wires at the thermostat and no house supplied power source except for the fan motor. It looks pretty simple, a thermostat, gas valve, over heat mercury switch and what I believe is a thermopile all connected in series.

I'm now wondering if maybe the thermopile is getting weaker over time and now it's at the point where it can't open the valve with the full circuit but can hold it open once the gas valve is jumped?.....

The thermopile puts out about:
>215mv with just the pilot light on
>270mv with the burner on(checked just after the burner is turned off)

My problem is that I can't find any specs on what the thermopile should put out or what the gas valve should open at so maybe some of you guys could give me some advice? Without any specs how can you tell if the thermopile or the gas valve is bad? ......or could it somehow be the wiring??

Any advice is appeciated!

**beenthere** · 11-29-2009, 05:28 PM

Bigger problem is your using a 40 year old 35% AFUE, unsafe gas furnace.

marchvac · 11-29-2009, 05:52 PM

I agree that furnace probably does not have one safety on it. You should be looking for a new one.

yuri · 11-29-2009, 06:17 PM

Freddy Kruger furnace, scares the heck out of me.

EVERY single Silverline in Wpg. is gone as the heat exchangers ALL cracked. Pull the fan and the cracks stare you in the face. Time for a new furnace and the 15% fed home improvement grant helps a lot. Expires Jan 31/2010.

avro1 · 11-29-2009, 07:29 PM

Wow.... After those replies I can't think of any reason to even keep trying to fix it....it's gone! Thanks guys.

What would you recommend to replace it? Brand? Effeciency rating? etc?

I'm just currious on how old this furnace is...any guesses?

**beenthere** · 11-29-2009, 07:41 PM

Determine what size furnace you really need.
Use This its easy. It has a 50 dollar fee.

Then check into getting a 90% or higher furnace installed.

As far as brand. Doesn't realy matter. If installed right. They pretty much all last a good long time. If installed wrong. they all have troubles.

yuri · 11-29-2009, 08:06 PM

That sucker is over 40- 45 yrs old. We had hordes of them here as TECO units. / T.Eaton Co. for old Canucks.

LOL. Get 2-3 quotes from reputable dealers and check the BBB. If you like to run your fan for circulation especially in a 2 story house buy one with a variable speed fan with an ECM motor. They only use 80 watts vs. 360 watts or more for a conventional type. Check with ATCO or the electric utility, Mb Hydro has a rebate for those motors plus the fed grant for home improvement. Do the heat loss calc. and get back to me. It may be low for our very cold climate. I would use a 80,000 BTU high efficiency unit and possibly a 70,000 if the windows and doors and insulation are upgraded. A 2 stage unit is easier on gas as it fires at 70 % for a good part of the season and 100% later. More comfortable also. Good Luck

avro1 · 03-17-2010, 01:29 PM

I'm not one to revive old threads but since this is mine I thought it would be okay.

Since this original posting I've decided to have the furnace replaced and some of you may remember my delema with my furnace "installer'....

Anyways I think we finally have a plan and since the furnace has been working more or less okay since this first post he was going to install it when it warmed up a little like around May. Well as of late the furnace has been going down hill pretty fast. it's gotten to the point now that it will only come on if I push that manual overide button on the top of the gas valve for about a second or two so to me it looks like the electrical side of things is about done.

I checked the open circuit thermopile voltage with just the pilot light on and it was about 80mv. Then I cleaned the pilot oriface as best I could and knocked a bunch of crap off of it. The flame is better and now I get about 170mv but still not what I had last fall and still not enough to open the gas valve so this trend tells me that the thermopile is toast and the gas valve is probably still "okay".

So what I'd like to know is if there is any way to "band-aid" this thing until it gets warmer and the furnace is replaced once and for all? Should I run out and get a new thermopile for these next few months and if so which one should I get? They all seem to be rated at 750 mv so would that be okay for this 50 year old furnace, I mean was 750 mv the standard back then too? I don't want to overpower it and wreck it when at least now it's sort of working.

Worst case is the thermopile totaly fails and I end up having to use the manual override on the gas valve(see close-up pic of gas valve). This will give me heat but there is NO protection. Not something to engage and then forget about and go to work!!!

Any advice is appreciated.

yuri · 03-17-2010, 02:22 PM

750 mv is all that is available and will work unless that was a 500 mv type (very rare). Depends on the physical diameter of the thermopile also known as pilot generator whether it will fit in the pilot burner. ALL the wiring connections: tstat and wiring from it and at furnace, limit control, gas valve must be absolutely clean and tight or it won't work. Try fixing those first and it may limp along w/o a new generator. You are going to need a new 24v tstat for the new furnace. I would go buy a new Honeywell FocusPro at HDepot and use it for this furnace. It will work as a tstat is nothing more than a switch and the new one will have less resistance than the one you have now and may make a difference enough to keep it going. If I had a furnace museum I would give you $50 for the old beast.

Actually that is a "high efficiency" furnace in Sask. Go Bombers Go.

avro1 · 03-18-2010, 01:01 AM

Thanks Yuri but I think it's starting to look like it's at the end of the line for this beast. The thermopile connections are sparkling clean and as of today the only way to get gas flow is to push the manual override and hold for a second or two. Even jumping the thermostat screws on the gas valve won't open the gas valve anymore.

I did do another mv check and got these results with the Multimeter connected to the thermopile terminals on the gas valve...

Burner off for a while but thermostat set to heat on I got 82mv.
Then I gradually heated the thermopile with a propane torch and the gas valve opened at about 116mv.
Then with the furnace running the mv's ended up at about 120 mv's.

Looks like I might have to find a thermopile some place and jerry-rig it to work until this beast gets replaced.

Oh if you really want this thing I'd even pay you $50 to take it. I'll be in Winnipeg this summer and I can bring it if you like!