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  1. #1
    Join Date
    Oct 2009
    Posts
    4

    15 Y.O. vented gas log shutting down intermittently

    This is a Heatilator GC300 vented gas log fireplace with a standing pilot. We use it probably 5 hours/day in the wintertime and it's been great until this spring, when it started to shut off at random intervals. Sometimes it will shut off (pilot always stays lit) after ten minutes, sometimes may run for several hours with no problem. When it does shut off, sometimes it will re-light in about a second, sometimes it may be off for an hour or so. Sometimes it will shut off, restart, then shut off again. Turning the wall switch off and back on seems to make no difference.

    Had a serviceman look at it in the spring and he said he tested everthing an could find nothing wrong, but it needed a through cleaning and adjustment, which he did. Shut it down for the summer shortly thereafter and this fall we find it doing the same thing.

    The switch is just a standard 120v switch, so I took it out of the loop and just hooked the two wires together with a wire nut to see if that was the problem. It still shut down after a while, so I doubt that's the problem.

    It appears to have a high limit sensor that must be in the exhaust stack somewhere according to the manual/install instructions I have. I can follow the wire from the gas valve out through the side of the unit but not sure where it goes. Can these fail intermittently? Can it be tested? Would it ever shut off after the fire has only been burning for a few minutes?

    I talked to a gas fireplace shop and he says "it's the thermopile" with no doubt in his mind. The intermittent failure makes me wonder -- can they fail intermittently?

    I've checked the exhaust vent outside by taking the end off and it doesn't appear to be blocked (vents through the wall immediately behind the fireplace).

    I have the identical unit upstairs in the master bedroom that probably hasn't had three hours' use in the 15 years, but it's pretty tough to just make them magically trade places <G>.

    Any advice on where to go from here?

    Thanks!
    Last edited by miatapa; 10-24-2009 at 07:07 PM. Reason: Add more info

  2. #2
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,302

    Exclamation

    Quit tinkering with it and get a pro in there. You could hurt yourself or cause a fire/ explosion.

    This is not a DIY site. You can contact Heatilator for the nearest tech to you. This is an old unit that is probably just getting tired and needs a new part or two and maybe improve some connections. Now that you've messed with the venting adds a whole new dimension to the problem not to mention you referring to a 120 vac switch on a standing pilot fireplace.

  3. #3
    Join Date
    Oct 2009
    Posts
    4
    I've had "a pro" in here and they don't appear to have a clue. "Messed with" the vent includes taking off the head and looking to see if there's a blockage and then replacing it. The 120 vac switch was the one that was installed 15 years ago when the house was built. And the "pro" assures me that the 120 vac switch is what they use on "all our fireplace installs," and that there's nothing to be gained by using a millivolt switch.

    I fail to see how I've increased a risk of explosion by doing two things that the "pro" should have done when he was here in May.

    To quote you "This is an old unit that is probably just getting tired and needs a new part or two and maybe improve some connections." That's what I thought until the "pro" told me there's nothing wrong with it . . .

    Would it make sense to have that "pro" switch all the guts of the fireplace with the one upstairs that has never been used?

    Thanks.

  4. #4
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,302

    Cool

    Sorry if I sounded harsh but I've investigated enough 'tinkering' results to warrant my warnings.

    If you are not trained in or familiar with these vent systems, you can put them back together incorrectly, which can lead to fire, carbon monoxide poisoning or operational problems. Some units require special sealant on the inner flue joints for example. Also, many times, those not familiar with these things will unknowingly damage the aluminun inner exhaust section. In this case, this termination does not require sealant but it does have to maintain a 1/4" per foot pitch upwards towards the flue gas outlet. Also, the air intakes cannot be blocked---see details below. If you damage any of the venting on this fireplace, you might as well tear the whole fireplace out as this venting is no longer available.

    If that switch is powered by 110 vac going to a millivolt valve, it is a hazard and must be disconnecetd and the valve replaced before continued operation. If you are referring to a switch *rated* for 110vac but serving a millivolt circuit that's entirely another matter.

    If there's nothing wrong with it, then why doesn't it work?

    If parts are available from the mfr. it would not make sense to cannibalize another working fireplace. You are always better off using new parts from the mfr. than old or re-used parts even if from that mfr.. Besides, you then turn the second fireplace into a non-functioning appliance.

    The thermopile powers the entire fireplace. It generates about 1/2 of one volt DC by flame contact. They get old and tired just like us so some days their voltage output falls off causing sporadic operation. Also, anything that can affect the pilot flame can cause such sporadic operation. You have to consider the appliance itself but also surrounding structures and conditions. Were there any modifications or additions to the home? Changes in prevailing wind? Is the gasket intact on the glass and is the glass properly sealed?

    The high limit switch is in an upper corner of the outerwrap of this fireplace--not attached to the venting. It is a two wired Normally Closed circuit that has auto-reset, if I'm not mistaken.

    This unit has fiber insulation in the combustion air intake that can fall apart to where it blocks incoming air. It is impossible to replace in the field. It can be seen with a mirror up the back plenum.

    Gas valves, too get old and tired. The years of being next to heat and eventually cause things to break down, seize up or fail. That valve is only rated 175*F. Also, it could have been partially clogged with debris.

    If you provide your area, we may be able to suggest one or two techs to consider.
    Hearthman

  5. #5
    Join Date
    Oct 2009
    Posts
    4
    Thank you very much for the well reasoned answer. I guess you're right that there are a bunch of possible causes, I'm just trying to eliminate the most common ones.

    It's a 120vac "rated" switch running the millivolt line, so apparently that's not the problem as I said that when I just wired it directly together with a wire nut the failure still happened. There is NOT 120 running through the line. Just trying to eliminate the possibility of some corrosion on the switch being the problem.

    I have no problem whatsoever paying to have it repaired properly, just not excited about the prospect of interminable $75 service calls without repairing/discovering the cause of the problem. If I get to that point, I'll just use it the way it is and let it shut down and then turn back on when it feels like it <G>, though that may not be the safest approach.

    I don't think anything has changed in the house, it was new (a model home) when we bought it in 1995 and we haven't changed anything. The surrounding area and buildings haven't changed for over ten years.

    I'm in Utah (Ogden) at zip 84403 if you could suggest anyone. Just "shooting blind" by using the yellow pages is kind of a crap shoot.

    Thanks for your help!

  6. #6
    Join Date
    May 2005
    Location
    Madison, WI
    Posts
    1,078
    Sorry did not read all of the other lenghty posts.

    Based off the GC300 model I can offer some tips a service person should look for.

    The glass seal on those units was often a rubber gasket attached to the unit, this dries up and cracks apart causing exhaust leakage into the house and weird air flow patterns in the unit. This can cause them to go out. The glass seal should be replaced with a rope gasket heatilator sells by the ft.

    Could be also be thermopile, valve, limit switch, etc...

  7. #7
    Join Date
    Oct 2009
    Posts
    4
    Thanks, I'll replace the gasket as well. BTW, it appears the intermittent shut down MAY be resolved, as it hasn't done it for days now.

    I found a crimped connection on the wire from the high limit switch to the gas valve that I think may have been slightly loose. I moved it around it that solved it apparently -- if it continues to work correctly, I'll replace the connection.

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