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Issue with my American Standard High Eff Furnace

TalltomTalltom Member Posts: 1
I have a dual stage American Standard Hi Efficiency gas furnace that was installed approx 2004.

In January of this year, I woke up one morning to a very cold house.  A service tech came by and determined that the condensate had collected and backed up and fouled the pressure switches.  He drained everything out, and ensured that everything was working correctly before leaving.  A few months later (as the weather began warming up) I noticed that the inducer motor was running a 100% of the time, even when there was no call for heat.  As it stands now, it always runs as long as there is power to the furnace.

The LED fault light is giving me the 3 quick flashes indicating a pressure switch problem.  If I power down the furnace, then power back up, the furnace will cycle and run properly. 

I've checked all of the drain tubes and they seem to be dry and free and clear of obstructions.

I'm wondering if the pressure switches may have gone bad simply from having had moisture in them previously.  And if so, if this is an issue of merely replacing them.  If it is merely replacing them, is this something that I can do without screwing anything up such as a CO leak or anything like that.

Any thoughts or suggestions?



  • lchmblchmb Member Posts: 2,513
    sounds like

    It may be a good idea to have someone come in and service the unit and correct all issue's prior to the heating season. Some things are best left to a pro, and this sounds like one of them..;)
  • Tim McElwainTim McElwain Member Posts: 3,904
    Good advice

    call a pro and make sure they do a combustion analysis on your equipment. The new furnaces and boilers by the way are not as forgiving as the old systems. Many of these new units require an annual cleaning. Condensate lines can be a definite problem along with plugged secondary heat exchangers and on boilers the fireside combustion chambers getting all fouled up.
  • TechmanTechman Member Posts: 2,144
    edited October 2011

    Sounds like it could be a patially plugged trap for the flue gas condensate. Shutting the unit down allows time for the trap to drain ,then restarting the unit the condensate will build up in the trap after running for a certain ammount of time. Remove the trap, use white vinegar in the trap ,shake,shake, shake and pour it down the sink drain. Flush w/ lots of hot water and junk should come out of the trap.Do that several times,until the trap is clear. Re-install and run . Upon a call for heat the furnace starts and flue gas condensate forms. Upon a back-up of condensate the unit trips off by the safety pressure switch and "locks out"after several attempts for heat .But the unit is still calling for heat so the "timer" for the fan brings  the fan on.
  • Jean-David BeyerJean-David Beyer Member Posts: 2,532
    a patially plugged trap for the flue gas condensate

    Have I been lucky or wise? I have my mod-con serviced annually, near the start of the heating season. One of the steps is to remove and clean the condensate trap. There seems usually to be a little sediment in the bottom, and the first year, the technician put some of the sediment in a little bottle and had it analyzed. It looked as though there were aluminum dust in it, and the heat exchanger is aluminum and this concerned him. It turns out there was very little aluminum in the sediment and the next time there was not any, so it may have been casting residue that remained after the unit was manufactured.

    But could a boiler come up with enough sediment to block the condensate trap in only one year? Especially since most of them I infer are made of stainless steel? Or is the one in question one that may have not had annual maintenance?
  • Tim McElwainTim McElwain Member Posts: 3,904
    Typically the condensate lines get

    plugged because they are not maintained every year. They should be pulled and flushed as they build up a residue when they sit all summer and there is no heating activity.

    I would on your Ultra make sure it is checked every year as they are susceptible to problems with the condensate removal. I am sure you know you have to have a cleaning every year with the Ultra so it should be done then.
  • Jean-David BeyerJean-David Beyer Member Posts: 2,532
    every year

    I do have my Ultra cleaned and checked every year. In spite of the fact that my former contractor said gas furnaces and boilers do not need annual maintenance. One of the reasons he is my former contractor. The new contractor does it annually, and always replaces the igniter even when it does not seem to need it. There is a standard maintenance kit that includes all the heat exchanger gaskets, the gas burner gasket, and the igniter (that is also a flame detector. So they might as well put in a new one when it is all apart for cleaning the heat exchanger. I keep the old one on a shelf next to my spare pressure relief valve and some slightly used Taco circulators. They all were in working order, but two of them were noisy and I wanted to replace them at my convenience instead of late New Year's Eve when I assume they would go by themselves. The third one was only about two years old that I salvaged from my old oil burner.

    My condensate trap is fairly clear semi-softsoft plastic, so if I pull the front off, I can make a superficial check to see if it is blocked or not. I would not consider this a definitive test, and it would be no substitute for periodic cleaning, but it would warn me in advance.

    My boiler runs all year because it is needed to warm up my indirect fired domestic hot water heater. Seems to burn a little over 4 therms a month to do that.
  • TechmanTechman Member Posts: 2,144

    Traps for furnaces are different then boilers.Some furnace traps are little ,black plastic ,un-take-apart-able, 1 1/2" x 2 7/8" x 4" or something like that. The stuff from the combustion air is part of the stuff in the trap. How many CFM of combustion air  for a therm of gas ? How many GPM or GPH or GPD goes thru the trap ?
  • Jean-David BeyerJean-David Beyer Member Posts: 2,532
    Condensate production rate.

    The maker of my mod-con boiler says to use a 2 gallon/hour pump for condensate removal. My boiler is rated at 80,000 BTU/hour, but I doubt it ever runs close to that except when the indirect hot water heater calls for heat. For home heating, I calculate that I need about 30,000 BTU/hour when it is 0F outside. I have never seen that. Design temperature around here is 14F and it goes below 10F a couple of times a year.

    When it is just above freezing, I can fill a 2 gallon bucket with condensate about once a day. I am sure I get more condensate when it is below freezing, but then the water in the bucket freezes, so I cannot tell how much is produced. In cold weather, a lot of "steam" comes out of the vent pipe, so I am not getting 100% condensation. When heating my large heating zone (at grade concrete radiant slab), the return water temperature varies between 75F  and about 110F under normal conditions, so I expect the system to run at between 98% to 93% efficiency.
  • Tim McElwainTim McElwain Member Posts: 3,904
    For a normal gas system

    atmospheric gas burners it takes 10 cubic feet of air for every 1,000 BTU's plus 4 cubic feet of excess air, add to that 15 cubic feet of dilution air at the draft hood for a total of about 30 cubic feet of air for every 1,000 BTU's.

    With fan assisted we do not need the dilution air so we have less air required per 1,000 BTU's roughly about 15 cubic feet. Burning 25 cubic feet of natural gas produces about 2.25 pounds of water. If a 100,000 BTU atmospheric furnace or boiler burned continuously for one hour it would produce slightly more than a gallon of water.

    A condensing appliance produces slightly less than that of moisture per hour if in a fully condensing mode and obviously with modulation cubic foot gas usage will vary and cycle rate will also affect the amount of condensate so it is hard to predict volume of condensate. I am sure there will be someone here from the engineering side who has calculated all of that out for us.

    I can tell you this I have seen times when the plastic tubing running from the condensate pump was too small and had to be enlarged. I tell everyone to go with 1/2" of more depending on input. Most residential furnaces are not much more than 125,000 BTU's if that so it is different for them than boilers.
  • MrDucksMrDucks Member Posts: 27
    Inducer Running With "NO CALL" For Heat?

    That code will show stuck closed, But NO CALL for heat. Check your grounds --- If OK Sounds like the board went. Any AC hooked to this system, Water during the summer??
  • MrDucksMrDucks Member Posts: 27
    edited October 2011
    Ultra Boilers

    Does your heating contractor use the Wei McLain Ultra Mantenance kit?  JDB
  • Jean-David BeyerJean-David Beyer Member Posts: 2,532
    Does your heating contractor use the Weil McLain Ultra Mantenance kit?

    My new contractor does. My former contractor did not: he would not even open the heat exchanger for cleaning and inspection "because it is gas and does not need it." That is why that outfit is my former contractor.
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