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#1
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Gas Furnace Question
On Dec 20 2009, 12:04*am, "CWLee" wrote:
How does a "vent safety switch" work? I'm trouble-shooting a friend's gas furnace (Empire Comfort Systems Model #GW-25-6). *I have isolated the problem to what the instruction booklet calls a "manual reset vent safety switch." *It says this safety device will switch off the gas flow if "the ventilation is not proper" or similar wording. *I'm trying to figure out if the switch is defective, or if there is a ventilation problem. *I'm satisfied that the pilot and burner mechanism work properly, and that the thermostat works properly. *Nevertheless, the furnace shuts off unexpectedly, but will restart promptly if the vent safety switch is reset, meaning a button on it is pushed. What variable does the switch sense in order to determine if the ventilation is proper? My first thought is that it is temperature, and that if the temperature of the air around it is above some threshold the switch cuts off the electric current that is keeping the gas valve open. My second hypothesis is that the switch senses air flow (how would it do that?) and if the speed of air passing the switch is below some threshold the switch cuts off the electric current that is keeping the gas valve open. Enlightenment, explanations, elaborations, etc. appreciated. -- ---------- CWLee Former slayer of dragons; practice now limited to sacred cows. *Believing we should hire for quality, not quotas, and promote for performance, not preferences. 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. |
#2
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Gas Furnace Question
"jamesgangnc" wrote If it's naturally vented (no fan in the vent system) ... Yes, that is the case here. then it's probably a rollout switch. 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. |
#3
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Gas Furnace Question
CWLee wrote:
"jamesgangnc" wrote If it's naturally vented (no fan in the vent system) ... Yes, that is the case here. then it's probably a rollout switch. 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. 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 |
#4
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Gas Furnace Question
"The Daring Dufas" wrote 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 ... The furnace in question has no fan to "force" the air flow - does that change your response? ... one or more roll-out switches are located around where the burners take in combustion air and air for the draft. The switches that were apparently defective, and replaced, were at least 3 feet above the pilot and burner area - does that change your response? 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. It does sound like a good idea to have such switches. Are they normally easy for the consumer to reach - or are they like the switch in question in this case, only accessible after removing 6 machine screws and a large panel? Thanks for continuing my education. |
#5
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Gas Furnace Question
CWLee wrote:
"The Daring Dufas" wrote 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 ... The furnace in question has no fan to "force" the air flow - does that change your response? ... one or more roll-out switches are located around where the burners take in combustion air and air for the draft. The switches that were apparently defective, and replaced, were at least 3 feet above the pilot and burner area - does that change your response? 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. It does sound like a good idea to have such switches. Are they normally easy for the consumer to reach - or are they like the switch in question in this case, only accessible after removing 6 machine screws and a large panel? Thanks for continuing my education. No problem my friend. I responded to your original post after I guessed it was a wall furnace which is so much simpler than a central forced air furnace. My responses wouldn't change because I was making comparisons between the forced air and the gravity furnace. The safety switches usually have a little reset button between the electrical terminals and when pushed in will make a little click sound when reset. When I check a malfunctioning furnace, I will go through and press all the reset buttons until I come across one that clicks. From there I can try to determine what tripped the safety. If I had a small house/cottage or an efficiency apartment, I think I would prefer a gravity wall furnace because of the simplicity and the fact that it would keep a home warm if the power was lost during a severe winter storm. TDD |
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