Results 1 to 10 of 10
  1. #1
    Join Date
    Sep 2008
    Posts
    7

    Blocked vent safeguard switch goes off repeatedly

    Hi,

    I have 58UHV HVAC. I just started using it this season and within an hour the "blocked vent safeguard switch" shut it off. I push a button on the switch to turn it back on and the furnace works for another hour, then the switch shuts it off again. I can say by touching a flue collar that it's hot, I mean real hot, almost like an iron on a low setting. I am not sure if this is the way it's supposed to be or if it means that I have a clogged vent.

    What should my next steps be? If the vent is clogged then how do you attempt to clean it? Do you have to actually detach the vent pipe from the flue collar or would it make sense to climb on the roof and see if the vent is clogged up there?

    Or would it make sense just to replace a safeguard switch and see if it goes off or not? How hot should the flue collar be under normal circumstances?

    A qualified technician looked at my furnace last year and also they cleaned the ducts. I am not sure though if that included cleaning the vent, now I doubt it. Even if I call them again I want to find out first what they SHOULD do to fix it permanently.

    Because last time the same thing happened but only once and all that young guy did was push the same button on the same safeguard switch (that's how I learned this trick). And that was enough to keep it running till the end of the season. Not this time though.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,922
    I'd get a tech out ASAP! Probably is a blocked flue but also could indicate other venting issues, not something safe for a homeowner to mess around with.

  3. #3
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,709
    stop resetting the safety until you get a competent tech out to take a look at it.

    not the one that reset it and left........


    quite a few conditions could cause the same end result.

  4. #4
    Join Date
    Sep 2008
    Posts
    7
    Thank you, I will definitely get a technician.
    Can you tell me what the normal temperature of the flue collar should be when the problem is fixed?

    Right now my furnace keeps working without me resetting the switch for quite a few hours. It bothers me that another technician may come, do some inspection, dust a few things off and since it does not shut off anymore he may just tell me that there is no issue.

    Just like it happened last time: the technician cleaned air filter and did some inspection and, well, he reset the switch and he left.

    Is it normal that the flue collar is really hot to the touch even if the blocked vent safeguard switch stays on? This is how it's been as long as I remember. The technician just mumbled something when I asked him about it. I need to get this info before I proceed.

  5. #5
    Join Date
    Mar 2003
    Posts
    1,234
    Just curious, is it windy when it shuts off? This has occurred many times and since it doesn't shut down every time I doubt you have an obstruction in the vent pipe. It may need to be extended higher above your roof also. That switch is set to open about 210-215 degrees and it draws air through the little opening by it to keep it below that temp. If the vent isn't high enough and the wind blows it can restrict the flow of hot air causing it to back-up and overheating that switch.

  6. #6
    Join Date
    Sep 2008
    Posts
    7
    Thank you for this info.
    No, it wasn't not windy.
    I also doubt there is any obstruction in the vent pipe. I looked at the vent on the roof: air is coming out of it and it is pretty hot when unit is working.
    Also, I took a vent pipe off a flue collar: it has some small specks of white residue and some corrosion inside for the first three feet, but it is not obstructed for the first 6-9 feet that I could see through before it makes a bend and goes vertically. There is no obstruction in the unit either. I vacuumed whatever I could but that's just some white white corrosion dust - not much.

    Would it make sense to install a new sensor - exactly the same as I have just to see if it ever trips over? Someone suggested that if sensor came off a few times it may do it more "easily" after that.

  7. #7
    Join Date
    Jun 2008
    Location
    Cincinnati, Ohio
    Posts
    2,176
    Quote Originally Posted by vasilybu View Post
    Thank you for this info.

    Would it make sense to install a new sensor - exactly the same as I have just to see if it ever trips over? Someone suggested that if sensor came off a few times it may do it more "easily" after that.
    This will not solve the problem, but it could be weakened due to the condition of the HX. Have the tech replace it also.

  8. #8
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    There is a good reason some safety controls are manual reset, it is an indication that there is a DANGEROUS condition that requires correction before continuing to operate the equipment.

    I strongly advise against repeatedly resetting manual reset safety controls in the future.

    Please call a tech out to look at it, and be sure and explain what it has been doing, and that you have reset it several times.
    Most likely there is something at least partially blocking the vent pipe, but there are other things that can cause that safety to trip.

    Quote Originally Posted by vasilybu View Post
    Can you tell me what the normal temperature of the flue collar should be when the problem is fixed?
    Somewhat lower than the temperature the safety switch trips at!

    But seriously, in normal operation, it will be to hot to touch, but there is a pretty big "normal" temperature range it could be, depending on a number of factors.
    If more government is the answer, then it's a really stupid question.

  9. #9
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,986
    The switch that you're resetting was put there by the manufacturer to turn the furnace off if a situation presented that could be dangerous. The safety warning on these kinds of safety switches ususally reads something like "can cause property damage, bodily harm or death!"

    The fact that it has a manual reset verses an automatic reset means whatever makes it trips is something that should be taken care of emmediately. Resetting it should only be done by a qualified technician after a complete safety check of the furnace and venting.

    I'd suggest you call whatever service company you feel comfortable with and tell them what is happening and that you'd like them to send someone that is qualified to diagnose this type of problems.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  10. #10
    Join Date
    Jun 2004
    Location
    Howell, Michigan
    Posts
    16,173
    Quote Originally Posted by vasilybu View Post
    Would it make sense to install a new sensor - exactly the same as I have just to see if it ever trips over? Someone suggested that if sensor came off a few times it may do it more "easily" after that.


    This is not a DIY help site. You need to call a technician before someone gets hurt or worse.

    Quit trying to fix it yourself!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event