# What exactly does the vacuum pressure switch do?



## Andy H (Oct 19, 2011)

My stove has been starting up fine and then running for about 15 minutes and then shutting down.  It's not getting to hot, it just shuts down.   

Well, I bypassed the pressure switch and it seems to be running perfectly fine now.

My question is..... what does this switch do?  I'm sure it's there for a reason, I just can't  figure out what. 


Is it safe to run it like this for a while until the new switch comes in?


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## jtakeman (Oct 19, 2011)

Ahhhhh! No it isn't safe to run with any sensor jumped out!  :ahhh: 

The vacuum switch monitors the amount of vacuum in the firebox. In case you have a plugged vent or major leak. It opens and shuts down the stove.


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## Delta-T (Oct 19, 2011)

what stove is this? sort of unusual to have the pressure/vac switch thing happen 15 minutes into operation.


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## SmokeyTheBear (Oct 19, 2011)

Andy H said:
			
		

> My stove has been starting up fine and then running for about 15 minutes and then shutting down.  It's not getting to hot, it just shuts down.
> 
> Well, I bypassed the pressure switch and it seems to be running perfectly fine now.
> 
> ...



The vacuum switch is the stoves way of knowing it has an airflow through the venting in the proper direction.  If the vacuum switch doesn't see a pressure difference it will not remain closed.  When it opens the auger is stopped depriving the stove of fuel and leading to shutdown.

You should never run the stove with the vacuum switch bypassed except to verify that the switch is out to lunch.  Also if you have a dual ported unit and hook it up wrong it will not work in the manner the stove expects.

Now it is possible you have crud in the tube that goes to the vacuum switch if the tube or its barb are plugged the switch will not close.  Disconnect the tube at the switch end and blow through it, this may not always work in which case remove the tube at the other end as well and use a pipe cleaner to clear the barb on the stove and then try blowing through the tube to clear it.  Once you have the barb and tube clear, reconnect, remove any jumpers and retry the stove. 

A shutdown at 15 minutes or so into a run is usually a proof of fire issue.  A temperature sensor or thermal snap disc isn't seeing the correct temperature.  Vacuum issues usually stop the auger from even delivering pellets at startup.


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## jtakeman (Oct 19, 2011)

USSC Forester. I think he asked this last season if my memory serves me.


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## Andy H (Oct 19, 2011)

Yup, Forrester 5824  but I don't think that info will help anyone since apparently only 2 of us in the whole world have this stupid stove and the other guy is also having problems with his.

and DUH... I just ran a search on my username and see that i did ask this last year but that turned out to be a clogged vent issue and not a vacuum switch issue. 

here is what i'm not understanding, the stove would run for 15 or so minutes and then beep and shut off while the flame was still going... there were plenty of pellets in the burn pot when it would shut down, it even shut down the exhaust blower so the fire would just linger.   You're saying if the switch was bad it would stop feeding pellets and the fire would just go out right?    That is not what my stove is doing.  

I did put a new high temp pressure sensor  in and that didn't fix anything, i even moved the sensor out of the stove (but still plugged in)  so it wouldn't get above 70 or so degrees and it still shut down

Can you guys think of anything else it could be?  I mean it's working without the vacuum switch bypassed so I'd guess it's that right?  but like i said  it would keep feeding it pellets right up to the point of it shutting down. 


there are two other low temp sensors in the exhaust area but I thought they were just to kick the convection fan on and off?  Could those be a cause of my issues?


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## Delta-T (Oct 19, 2011)

I'd guess low temp sensor before anything else...and might just be dirty. One might be to engage the blower, but the other is the "proof of fire" sensor so the unit knows its running. It may be wired in with the vac sensor, but I dont know that for sure. The 15 minutes is usually when the Control Board promps the POF switch and it it doesn't detect propper temp it shuts down.


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## SmokeyTheBear (Oct 19, 2011)

If your vent is clogged there will not be proper air flow or vacuum in the stove, the vacuum switch should open stopping the stove.


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## Andy H (Oct 19, 2011)

sorry, I forgot to reply to that part of your post Smokey,  I'm 100% sure every part of the stove is clean.  I took the whole stove outside and spent a couple hours cleaning every single part of it out with my vacuum and air compressor, including the hose that goes from the burn chamber to the pressure switch. 



if the low temp switches  could be the issue I'll replace those.


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## Don2222 (Oct 19, 2011)

Hello

See my post on testing the vacuum switch with pictures!

https://www.hearth.com/econtent/index.php/forums/viewthread/80407/


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## SmokeyTheBear (Oct 19, 2011)

Andy H said:
			
		

> sorry, I forgot to reply to that part of your post Smokey,  I'm 100% sure every part of the stove is clean.  I took the whole stove outside and spent a couple hours cleaning every single part of it out with my vacuum and air compressor, including the hose that goes from the burn chamber to the pressure switch.
> 
> 
> 
> if the low temp switches  could be the issue I'll replace those.



Did you clean your venting.

Are all sensors and switches back to where they should be and when you were playing with that vacuum and compressed air did you stay away from the vacuum switch, it is possible to damage them if you apply to much pressure or vacuum to them.

Do you own a multimeter?


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## jtakeman (Oct 19, 2011)

I would think the POF switch would not shut everything down. It shut tell the control no fire is present and go to normal shutdown(All fans to high for 5 minutes or so, Then shutdown). But I am assuming again. Not owning one this would only be a guess.

Funny jumping the vacuum switch keeps it going???? Don does have a point it could just be a bad connection???

Just for giggles, I'd hook the switch back up and fire stove as normal. But open the damper more. This would comp for say a leaky seal or something. Another is you might be able to increase the combustion blower speed with the control panel. I'd also like to see your venting configuration JIC. Excessive EVL????


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## Andy H (Oct 19, 2011)

The venting is also clean, and i'm not getting the lazy flame at all like i do when something is dirty.   the thing could be roaring and it would just go out.

I even turned it on when it was outside (no exhaust vent hooked up) and it did the same thing.

Edit:  just to make sure i answer all your question so I can get the best help possible,  it was doing this before i took it out to clean it.  Everything was cleaned and all the wires were connected back where they should be, i was very careful about this

when i brought it back inside it did the same thing... the cleaning didn't help at all.


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## jtakeman (Oct 19, 2011)

Evil stove gremlins!

I have also seen the wires at the molex connector start to pull out as the stove warms the connection is lost. Checking for loose connections is a royal pain, But it could be your issue???? Guessing again!


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## Delta-T (Oct 19, 2011)

j-takeman said:
			
		

> Evil stove gremlins!
> 
> I have also seen the wires at the molex connector start to pull out as the stove warms the connection is lost. Checking for loose connections is a royal pain, But it could be your issue???? Guessing again!



Stove gremlin are the worst.....the worst I say!


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## Andy H (Oct 19, 2011)

I'm on the USSC stove website and they have the 125* Sensors   If you guys think that could be what it is i'll buy them.  i just don't want to waste my money if there is no chance that is what it could be.


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## jtakeman (Oct 19, 2011)

You can jump it just like the vacuum switch. Just to try though, I don't recommend burning long periods with sensors jumped.


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## SmokeyTheBear (Oct 19, 2011)

Check your connections to the control board as Jay is suggesting, add the combustion blower motor connections to the list, and the vacuum switch connections.  

You should also check any wires going near the hot parts of the stove or through any pinch points.  Make certain the stove is off, cold, and unplugged.


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## jtakeman (Oct 19, 2011)

Delta-T said:
			
		

> j-takeman said:
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Next is them danged "glitches" and don't forget about them "quirks"!


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## SmokeyTheBear (Oct 19, 2011)

Delta-T said:
			
		

> j-takeman said:
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This bunch is even worse they were both feed and watered after midnight.


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## SmokeyTheBear (Oct 19, 2011)

Andy after checking the connections and giving the stove a start my next suggestion is to call USSC.


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## SmokeyTheBear (Oct 19, 2011)

Andy did you check your door gasket and is the door closing tightly?


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## Andy H (Oct 19, 2011)

j-takeman said:
			
		

> You can jump it just like the vacuum switch. Just to try though, I don't recommend burning long periods with sensors jumped.




ok, here is a dumb question,  How do i jump them?   

this is how the sensors are wired, do i just hook the black wires together?


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## archie79 (Oct 19, 2011)

I'm new to pellet stoves in general.. So with verry little knowledge, I purchased a pf 100, and installed it in my house last week... I was just wondering If anyone else has installed the pf 100 with an ac unit? Also if I wired the stove into the thermostat I control my ac with, would that be a "no no"... I know the thermostat that is supplied with the stove is a 3 degree variance thermostat and v/s the 1 degree difference for my AC unit..anyways thanks in advance!


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## SmokeyTheBear (Oct 19, 2011)

Andy H said:
			
		

> j-takeman said:
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Yes


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## SmokeyTheBear (Oct 19, 2011)

archie79 said:
			
		

> I'm new to pellet stoves in general.. So with verry little knowledge, I purchased a pf 100, and installed it in my house last week... I was just wondering If anyone else has installed the pf 100 with an ac unit? Also if I wired the stove into the thermostat I control my ac with, would that be a "no no"... I know the thermostat that is supplied with the stove is a 3 degree variance thermostat and v/s the 1 degree difference for my AC unit..anyways thanks in advance!



First off welcome to the forum.

You might want to start your own thread with title such as:  Is a 1 degree swing thermostat going to cause a problem with a Harman PF 100


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## archie79 (Oct 19, 2011)

Sorry thought I was starting a new thread... Will do that


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