old switch is unreliable and i suspect it has been since installation in the late 1990's (gas cuts off, re-lights - does this every cycle which i had thought was a normal "average temperature" mechanism: but lately it's doing it a few times a cycle - it's not normal). if i knock it or pinch the tube: the gas goes out. anyhow it's what clicks just before the gas gets cut off. what fun!

i ordered a replacement.

it's a diaphram switch (with a 2-lead relay piggy-backed). the label says "mount diaphram vertical"

I SEARCHED THIS ON BING AND THE MFG DOESN'T HAVE INSTALL INSTRUCTIONS AND NO-BODY SHOWS THIS MODEL - THERE ARE NO FORUMS ASKING OR ANSWERING.

Here's my issue:

(1) a diaphram is subject to gravity, so right side up and upside down on the pin axis makes a difference. mounting the pin of the diaphram switch vertical (it's main axis) allows proper movement of pin - but up or down matters for small wc pf ratings.

(2) if the "diaphram" diameter is mounded vertically the pin is horizontal. small issues (leak, slight imbalance) would cause movement failures due to it "cocking" going \/ during movement.

but which axis is right? does diaphram mean diaphram unit (pin axis is vertical) or does diaphram mean the membrane diameter (pin axis is horizontal) ?

the sensor that "never worked" had the diaphram membrane diameter vertical / pin horizontal. but that unit/brand is an import and doesn't say anything about how to mount it.

If your testing a car vacuum line and pinch it, it should HOLD vacuum not loose it. Maybe the switch was poorly manufactured or installed wrong.

Your forgetting the relay can also have movement issues. The way it's oriented can be important. If you mount the "membrane" vertical then you need the right o'clock orientation?

Where did the original installer mount it? If it's a differential it may work if hot (though not suggested). But if it isn't and you heat it up - it may expand gas inside the "empty" side and cause extra pressure on the wrong side.

Insure a professional works on your unit and insure it gets "inspected".

If this is a high efficiency power vent gas furnace then chances are the water trap needs to be cleaned out or there is a problem with the vent, a restriction of some sort. I have seen everything in the power vent tubes from leaves, bees, bird nests to bats. Additionally I have also seen problems with water build up due to improper vent tube hanging and incline.

I find few pressure switch problems, more system and vent problems.

Pin axis vertical.

I gather it's measuring something that's around inches of pressure, so it is shock sensitive.

HGMCU Wrote:
-------------------------------------------------------
> If this is a high efficiency power vent gas
> furnace then chances are the water trap needs to
> be cleaned out or there is a problem with the
> vent, a restriction of some sort. I have seen
> everything in the power vent tubes from leaves,
> bees, bird nests to bats. Additionally I have also
> seen problems with water build up due to improper
> vent tube hanging and incline.
>
> I find few pressure switch problems, more system
> and vent problems.

the installer could also installed the wrong "wc pf" rating

there is just 2-3' of horizontal vent and it's inclined - the rest is straight up. i didn't check for a bird nest. but i know the gas water heater sucks air when on (a lighter near it's vent opening pulls flame toward it.

(i mean when the wh is is on and the hvac is off - i followed some suggested test i found on the web to hold a lighter to see gasses were going up tube not in housing. have no idea how "good" the test is.)

dpcwk Wrote:
-------------------------------------------------------
> Pin axis vertical.
>
> I gather it's measuring something that's around
> inches of pressure, so it is shock sensitive.

interesting. i think an un-named company installed them all 90 deg to your suggestion.

that would mean many customers were calling for service and replacement frequently for the wrong reason

Pull the vent off at the furnace, often the input has a screen and you will see if any debris is on the screen, these systems are designed to be SENSITIVE so almost any debris will cause problems. Also the water trap can be clogged up. I find that pollen often build up in the water trap, it is a PITA to get out at times, but you can open it up and see the crap inside. A few minutes at the kitchen sink and some warm water you are good to go.

Also make sure the vent motor spins freely as well. Have seen many motors get tight and not spin freely as well.

These sorts of issues never arise in a properly maintained and serviced unit. Find your local competent HVAC company and sign a service contract with them.

Dealing with gas systems is extremely dangerous. If a mistake is made it can be left unnoticed and that is not safe. My choice is to ask for help specialists. Any gas service. Other systems can be installed safer. Like, plumbing, even electricity isn't that perilously. But what we also have to worry about is garbage and its collection. You need to choose the best garbage disposal units. That might look not so important but I'll disagree with such opinions.

Get on the bus Wrote:
-------------------------------------------------------
> These sorts of issues never arise in a properly
> maintained and serviced unit. Find your local
> competent HVAC company and sign a service contract
> with them.


dickhead. that's how the problems started. DNC democrats in fx co are letting companies run wild

the problem started with a well respected company installing it

Lobster Wrote:
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> Dealing with gas systems is extremely dangerous.

that's what makes this so much fun !

((i didn't mention what else the company did i already fixed: water collection dumping onto electronic control board & puddle on floor, igniter close to touching metal, loose grounds. incorrect sticker placed for control board light flashes. no insulation (heat barrier) on fumes motor installed - perhaps causing early failure of fumes motor. perhaps denting fan impeller (causing need of re-balance) - though i might have done it i don't remember doing it. 3 maintenance visits a year for at least 5 years without fixing any of the problems - always worked they day they left and began again soon later))

that's the certified respected company in fairfax. the fact is none of the area contractors ever use anyone certified like they did in the 80's: certified people never even visit worksites anymore - they just are "attached" to companies to allow (fairfax county gov allows) unqualified laborers to work where they shouldn't be allowed to work

((the xformer was fried i had to attach a new one onto the board - board appears to still work well after all that))

((the xformer was fried i had to attach a new one onto the board - board appears to still work well after all that))

everyone shows the things mounded not with pin vertical but with diaphram vertical - maybe my old one works pin vertical. and it was like that new.

i ordered a new one jic the old one begins acting up again. but i'm sure it's working i tested it.

the new ones might well be a ploy to get people to order them due to incorrect installation: if so. well, i ordered one. #damn

((the loose grounds were fun to diagnose and find. i have a spare capacitor i ordered i didn't need: symptoms were the same))

People are always blaming the pressure switch but 90% of the time the switch is fine and there are issues with the venting.
Naturally aspirated water heaters generally do not have pressure switches and will vent in less than ideal situations. The draft from the furnace can easily be measured with a good incline manometer. The incoming gas pressure and the manifold pressure should be checked and adjusted if need be as well.
A Dwyer 1227 is a great manometer for measuring gas pressure and it has magnets so you can also attach it to the duct and it can measure flue drafts as well by using the incline scale. Digital manometers are available too but are much more expensive.

pinecone