On Sat, 19 Dec 2009 21:04:35 -0800, 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.

Well, how do exhaust combustion gases leave the property? If the
exhaust is 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.

I'd check the exhaust first, make sure it's clear of any obstruction
(dirt, leaves, ice, dead critters, bug nests etc.) and only worry about
whether the switch is defective after you've ruled the exhaust out.

*don'* bypass the safety switch, obviously :-) If you want to rule out the
switch, buy a replacement and do it that way...

cheers

Jules

replying to Jules, fluemaster 5 wrote:
Well, how do exhaust combustion gases leave the property? If the exhaust is
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.
I'd check the exhaust first, make sure it's clear of any obstruction (dirt,
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!*

--
for full context, visit https://www.homeownershub.com/mainte...on-413635-.htm