About to attempt to fix my House Heater - no heat

movingzachbDecember 22, 2008

I have just signed up for this forum - and no i have not done a search but I will. I just want to post while things are fresh in my mind.

I have been doing some research to find out what is going on with my heater. I am looking for some free online help - as it is the time when I NEED heat now and cash flow is simply not available to pay for a service to come out and fiddle with it.

I have a Robert Shaw 9600 Thermostat - everything seems to work but there is no heat blowing. I can turn it on and hear it buzzing on the roof (opening the unit I can see its the fan engine spinning).

What I have done is:

- The 9600 Has a (in order) Red, White, Yellow and Green wire. Between the Common and the yellow or green wire I get 28 on the Voltage meter. White and Common I get .14. All other functions of the Robert Shaw 9600 Thermostat appear to be working.

- Got up on the roof and checked the units fuses - look fine.

- When it is powered on the fan motor starts and then you hear a minor click where it is attempting to ignite gas but nothing is happening.

- The solenoids don't appear to be getting power to ignite it, I verified this by checking the voltage coming from the Johnson Controls MG770 NGC-7 (this is an older unit there replacement is the Johnson Controls G770NHC-1C).


This unit is screwed in and looks very simple to replace as long as I put everything back in the right order with the new unit.

What I am concerned about is that I did read something about a exhaust fan being plugged or something like that. Where could make and adjustment to allow air to blow and ignite the gass (and this could be the issue) - however after checking voltage on the Johnson Conrtrols unit - this tells me the unit has failed I also wonder then how the fan is getting its power (maybe its routed differently and my heater is just locked out).

Here is where I posted my question still yet to be answered on the fixya site.


Any help or assistance with how to go about this is much appreciated.

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Guessing that the ignition module is bad is likely to be an expensive mistake. The problem needs to be diagnosed correctly.

This looks to be an intermittent pilot ignition system. That means that each time the thermostat calls for heat, the pilot light is lit by a spark, the fact that the pilot is lit is verified electronically and then the ignition module turns the main burner gas on.

You could have a variety of problems with the symptoms you have --- such as no gas coming into the furnace. Are you seeing a spark at the pilot light to light the burner? Is gas coming out of the pilot burner but you are not getting a spark to light it?

To diagnose the proble accurately, you need to understand the ignition control process and eliminate possible causes of the problem. Also, buying a different model control often means the arrangement of leads is different and it may require an understanding of how the new control should be set up to get it to work.

    Bookmark   December 23, 2008 at 11:12AM
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First. What type of unit is this? You might have a spark ignitor or a hot surface ignitor. If you have the hot surface ignitor, then you need to check the voltage coming to the ignitor. There should be a plastic harness clip that will come apart. You need to stick your leads on the two wires coming into that harness. You should get 120 Volts. If not, then you have a bad control board. That is if the induced draft motor is closing the pressure switch. If you are hearing that click in the control board after the inducer motor has come on, then you should get voltage to that harness.
If you have a spark ignitor, and you hear that same click from the control board, that should be the gas valve opening. But, if you do not hear the spark ignitor ticking, then you have a bad board as well.
I hope this helps a little.

    Bookmark   December 24, 2008 at 9:20AM
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The board is clicking - I do hear that when the power is turned on. There is gas - I can hear and smell it. - We checked the wires connected to the Intermittent control module (pilot). No power is coming from any of the cables connected to that module. I already verified that this replacement module I mentioned is a replacement (meaning a replacement for the old module by the company) - basically the same thing - new model number. I verified this by reading the PDF manuals from the Johnson Controls site.

I don't think it would really be that difficult to reconnect the wires on the new one where they went on the old one accordingly.

I don't know if it is a spark ignitor or a hot surface ignitor. I am guessing a spark. - Thing is - when it is powered on I can hear a click click. click-click - but it doesn't fire because no power is getting to the solonoids. The wires getting to the solenoids are coming from the Jonson Controls module.

    Bookmark   December 26, 2008 at 9:07AM
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movingzachb, you don't have a clue as to what the hell you're doing playing around with your gas furnace. You have to understand exactly what is supposed to happen and when. One screw up and KA-BOOM there goes your house and maybe your whole family! Is that the way to save a buck? Hell no! You've been dicking around for what four days now? Enough already, call for help. And you new guys who are trying to help him here. What are you going to do if this guy burns his house down and he gets a slick lawyer who trys to go after the people in the forum who gave him instructions he shouldn't have. Whats written in the documentation of every heating part that is ever replaced in any system? "THIS PART MUST BE INSTALLED AND SERVICED BY A TRAINED,EXPERIENCED SERVICE TECH". Now just why do you think that is? Take it from someone who's been hanging around in this forum for a long time. Figure out when to give advice and when no too. Do the words "accessory to the fact" mean anything to you?

    Bookmark   December 26, 2008 at 3:38PM
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m4.hvac - I know what your saying - really what I want to do is learn what is wrong so I can be come aware of what is going on and how to fix things - I just like to know how things work..

I remember watching an old Andy Griffith episode where Ant B refuses to fix the noisy refrigerator and Andy would keep tell her - Call the man. So I have made that slogan a household phrase. "Call the man". So I am certainly not opposed to it - but I am also one who likes to feel good about being able to fix something myself. I love the Internet and the ability to research things - so naturally that is why i am asking questions.

I understand your warning - but a nice articulated response will do fine :) Don't worry I am not going to do anything without calling the man - but I have been able to find out a lot of things on the Internet in the past that have saved me LOTS of money.

I fixed my cars smog, replaced a sensor and got it to pass smog. I also replaced a CAS O ring on it and saved 300 bucks at a mechanic. It is worth a try :)

I know that this is a trade-off if this was happening in the summer I would have more time to research it - but now its comfort over cash flow.

It is a spark ignitor - I will probably call someone I want a diagnostic though to find out how much they will charge me. I know that some of these places can find a loose wire and charge you 300 bucks and say its something else. I am not trying to be overly cautious - but if and when I do have someone come out to fix this - I will make sure I know exactly how it was fixed and what was wrong.

I know that many problems can be fixed VERY simply and I don't want some fix-it guy to "overlook" that :)

    Bookmark   December 26, 2008 at 4:33PM
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"but a nice articulated response will do fine :) If you want a nice articulated response I charge for them and I should warn you I am high priced and on holiday rates presently.:) So who do I send the bill too? One thing you should understand, with gas, many times you don't get a second chance! Mistakes when working with heating equipment can mean a house literally being blown off its foundation and occasionally an occupant whose body parts have been scattered about the neighborhood. I'm sorry if that too is to inarticulate for you but I'm a heating technician who has seen his fair share of screw ups in the trade not an English teacher. You want to learn, ask the experienced tech who comes to fix your system.

    Bookmark   December 26, 2008 at 5:02PM
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Dear MR HVAC here we go again with the doom and gloom.You sound very much like our out going administration.I think most responsible homeowners would like to be educated about there mechanical and electrical system so they can make informed decisions.Not scared into believing these system are so dangerous and complex that only a paid technician can fathom them.See my post:Gas valve failure

    Bookmark   December 27, 2008 at 8:18PM
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OK howtan1, just how do you know that the person who is giving you advice in a forum actually knows what they're talking about? For all you know they could know then you do! Hell over the years there have been supposedly experienced technicians advising in here that shouldn't even be doing such mundane jobs like changing filters! If you look at any paperwork pertaining to heating equipment I guarantee you will see the words "By a trained and experienced service person" I guess you think the manufacturers are also spreading "doom and gloom". Hey, do what the hell you want, its your own house just remember this is an open forum, if you don't like the responces you get what you pay for!

    Bookmark   December 27, 2008 at 11:59PM
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Actually mrhavac,
If this was a boiler or watersource heatpump or anything else other than a furnace that has multiple safety limits and switches, I would not help this guy out. But seeing as how he has a furnace and will not blow up his house unless he jumps out every single safety limit and switch, I figured I would give him a little help, and for the record I do know what I am doing, and if you have any problem with the troubleshooting advice I gave movingzachb then tell me where my advice was wrong.
I have a feeling you're not much of a people person.....maybe even a little pretentious.

    Bookmark   December 29, 2008 at 9:36AM
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"I have a feeling you're not much of a people person.....maybe even a little pretentious."
Oh really tlewis??? Funny, in all my years I've never been accused of that before. I'll tell you one thing about me though. I'm not someone thats going to sugar coat anything, if I think someone has no business inside their system I won't think twice of voicing my opinin. Maybe you're an overly sensitive and extremely naive little individual tlewis. Perhaps you should go over this entire thread again. It seems to me this guy is having a problem with his gas heating system. Incidentally he himself said he smelled gas! So he thinks he could go on the internet, type in a question or two and "glory be" his problem it solved! But its possible he could kill himself trying. Its been days now and this guy is still monkeying around. How do you know at this point if this system isn't totally scrwed up. Is the internet anyplace to learn about gas furnaces? NOT! "Gee, I wonder where this loose wire gets connected to!!!" I suppose your going to explain to this guy how to check all the safetys in his system too. If you're in this trade tlewis I hope you don't work this way with your customers. I don't know about you but when I work on a system, even if it was something simple, I go through that entire system. I check every safety, every wire, every sta-con, "everything" If I remove a wire nut I always cut back and strip insulation this way I know I have a nice new clean tight connection. Maybe in your mind I'm not a people person but I'm one hell of a conscientious technician who customers and less expereienced techs ask for. I also think I'm a pretty good judge of people and know when somebody should bail out. I hope someday being a little goody two shoes doesn't end up biting you right on the keester! Its a crazy world out there!

    Bookmark   December 29, 2008 at 6:08PM
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Oops....I guess I hit a nerve.

    Bookmark   December 29, 2008 at 10:11PM
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Forum rookie! :-)

    Bookmark   December 29, 2008 at 10:36PM
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