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Gas Furnace Question

Just don't go to the hvac group unless you like being abused.

Reply to
Bob F
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You havn't been on alt.hvac? I call it alternating havoc. It's been a bit slow, lately. But mentioning a thermosat there. It's like throwing bloody chum to starving alligators. Take a couple Valium before reading the replies.

Reply to
Stormin Mormon

Yes, it makes perfect sense. Now, the questions. Is there really a venting problem, or is the switch growing weak? Does the switch read pressure, air flow, or temperature?

Reply to
Stormin Mormon

That's exactly what I'm trying to determine.

An off-line continuation of this thread with one of the posters leads me to believe that it is a temperature sensing device. It may be called a thermodisk or thermodisc. I'm told the red dot on it signifies that it trips at 195 degrees.

One of my ideas is to remove it, take it to a heating/plumbing supply store, and see if I can match it. Once I have it removed I may be able to do some bench testing to see if it is working. My off-line advisor said the switch should "click" when it is reset. So far, I can't get it to click, but access is difficult so I'm suspending judgment until I have it off the furnace.

Thanks for your continuing assistance.

Reply to
CWLee

Many snap disk have a temperature number on there, some where. Maybe the wall heater manufacture can sell you a new one, and be done with it.

Reply to
Stormin Mormon

As the OP on this thread, I report on closure:

I did install a new vent switch, but that did not really change the behavior of the furnace. My friend explained the matter to the landlord, and eventually, for $169, a technician arrived to diagnose and fix the problem. He said the "stop" switch was not working, pointing to the vent switch I had installed. My friend explained that it was brand new. The technician repeated that it wasn't working, and added that it was the "wrong kind". He removed it, added a similar looking switch and that seems to have solved the problem. I have not had a chance to get a really close look at the new switch to see how it is different, but the furnace does seem to behave normally now.

Thanks to all who provided help on this situation.

Reply to
CWLee

I repair roll laminators for a living...GBC Seal Laminex USI Ledco Idex, and others..

Always find it funny that customers who tried and failed to fix something, when told of the real problem say thats not it now fix the problem.

this has even happened with manufactuers who sent me on warranty calls.

thats not it, now fix the problem... they hadnt a clue:(

I have asked them so why did you call me if you knew what would fix it???

a experienced tech has seen all sorts of wierd troubles, and had to solve them previously. part of what you pay for repairs is buying that experience..

Reply to
hallerb

If it's naturally vented (no fan in the vent system) then it's probably a rollout switch. If so then you have draft problems. Hold you hand near the switch when the unit starts. Feel hot air? If so that's exhaust gases that are not going up the vent. If you don't feel anything then replace it.

Reply to
jamesgangnc

"jamesgangnc" wrote

Yes, that is the case here.

Although the problem has been solved, I'd like to know just what a "rollout switch" does. Can you explain how it works? I've Googled "rollout switch" but all I learned were places to buy them, not what they do or how they work. Is it a switch that does anything more than shut off a circuit if the temperature sensed by it exceeds a specified level?

Thanks for any enlightenment you can provide.

Reply to
CWLee

It's sad that I have to explain to people that the product I sell is my time, knowledge, expertise and experience, not parts. When a lawyer hands you a couple of sheets of paper with some printing on them and says that will be $150.00, there are people who won't bat an eye but I spend a couple of hours figuring out the intermittent problem they're having with their latest new whizzbang technowidget and hand them a bill for $150.00, the same folks will have a fit. There are some people who aren't charged a dime, like the elderly mother of a friend.

TDD

Reply to
The Daring Dufas

From what I've read, it appears that the problem was a vent safety switch which is similar but not the same as a roll-out safety switch. On a forced air furnace one or more roll-out switches are located around where the burners take in combustion air and air for the draft. If the flames "roll out", ie, come out backwards from the burner assembly, the safety switch(s) detect this and shut down the furnace. Roll-out switches are usually manual reset like most safety sensors.

TDD

Reply to
The Daring Dufas

partially jammed then I can see that giving the behavior you're getting - the switch will trip because with the furnace running gases don't clear the exhaust fast enough, but as soon as the furnace is off (because the switch trips) the gases "slowly" leave the exhaust and pressing the reset lets it run again.

leaves, ice, dead critters, bug nests etc.) and only worry about whether the switch is defective after you've ruled the exhaust out.

*All, This may be due to an uninsulated flue stack on a flat roof with stagnant cold air outside. A cold air plug in flue may cause local gas accumulation & explosion blowing out pilot and tripping vent safety switch. Try insulating your flue stack from the roof up. This may also prevent water vapor condensation and rust from H2S in gas supply forming sulfuric acid. Good luck!*
Reply to
fluemaster 5

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