90+ gas furnace problems

[hvactech1jm]

alright a senior tech at work has been working on a bryant 90+ gas furnace he said the gas valve was bad so he put a new one on and it did the same thing so he got another gas valve it did the same thing. what it does is the HSI lights up and starts to go out and about that time the gas valve opens and putters and spitts and trys to come on. what i think it is is the HSI is not building up enough resistance to open the gas valve like it should and sending a weak signal but of course im young tech so they dont take my advice. any ideas what it might be.

[BaldLoonie]

Hate to tell you but there's a reason they don't take your advice! You got some learnin' to do. The ignitor doesn't build up resistance to open the gas valve. The valve is powered by 24 volts from the control. Hopefully the senior tech has the training to properly diagnose this then explain to you what he found so if you run across it in the future, you'll know what to do.

[skippedover]

A good tech will, before comdemning the gas valve, check for voltage to the gas valve. In a situation like you've described, I'd run it through a cycle and check when power if applied to the gas valve, all the while watching the igniter to see when it drops out. If the igniter is a silicon nitride unit, the frequency to the igniter might be too low, thus causing the problem. My first inclination would be to check with the manufacturer if I don't have the cycle specs at hand. It could be a bad board but it could also be interference from some other electrical source. As an example of how extreme those problems can be, our company once followed the manufacturer's specs exactly, including installing electrical filters on the incoming electics, replace wiring harnesses, gas valve, control board, igniter and finally, the whole darned furnace!!!! Still had the same problem. Factory finally said, switch the phases on the unit. We switched it at the C/B panel and the problem went away. This was in a very small U.S. Post Office and apparently there was some postal equipment creating electrical noises that affected the main control board. In that case, the SiN igniter received a different frequency through each start cycle, each one less than the previous one until the furnace wouldn't light. The control was then supposed to do a purge and then step the frequency back up to the last level that lit the fire. Unfortunately, with the electrical noise it was receiving, the control would just go into a lockout mode. So knowing the manfucature's specs is hugely important these days. Guess work is a thing of the past.

[jibroni69]

Strange, sounds more like the time delay built into the board is malfunctioning, check the HSI for voltage and exactly when the 120v is dropped from the HSI. I suspect the board is dropping the HSI too quickly, it cools a bit and the gas valve opens. These are 18 second HSI's are they not? Double check the sequence of operations on this particular model and time when the gas valve cuts in, also check the voltage at the gas valve, weak voltage could account for valve opening late. Could be a number of things , but resistance means nothing on this one.

[sarpanch2001]

Hate to tell you but there's a reason they don't take your advice! You got some learnin' to do. The ignitor doesn't build up resistance to open the gas valve. The valve is powered by 24 volts from the control. Hopefully the senior tech has the training to properly diagnose this then explain to you what he found so if you run across it in the future, you'll know what to do.

thats good lesson ;):)

[hvactech1jm]

so your saying no matter if the hsi lights up or not it will open the gas valve. i always thought the hsi had to build up a sertin amout of resistance befor the gas valve opened.

[jibroni69]

so your saying no matter if the hsi lights up or not it will open the gas valve. i always thought the hsi had to build up a sertin amout of resistance befor the gas valve opened.

exactly, first thing that is going to happen is the board will check for continuity to safty limits, if this checks out good the inducer fan will start up. Then when the preasure switch closes, proving venting the board will continue with it's set sequence of operations. First it will start to power up the HSI for a set number of seconds, at a set time the gas valve will open and hopefully the gas will be lit by the HSI. The gas valve does not care whether the HSI worked or not. There is no check by the board to test the HSI while it is operating. Once the gas valve has opened the flame rod sensor has about 2 seconds to prove there has been ignition or not. If not the board will shut off gas valve and start sequence over again. After 3 tries it will lock out the furnace and throw a code.

The HSI is really the dummy in the equation, the board doesn't care or check whether it works or not. It has nothing to do with nothing. :)

[rayr]

SENIOR TECH??????? LMAO. I'd hate to see the Jr. techs diagnostis!!!!!

[hvactech1jm]

no one asked for a smart ass i was just looking for some help.sorry you new everthing the day u started.

[hvactech1jm]

exactly, first thing that is going to happen is the board will check for continuity to safty limits, if this checks out good the inducer fan will start up. Then when the preasure switch closes, proving venting the board will continue with it's set sequence of operations. First it will start to power up the HSI for a set number of seconds, at a set time the gas valve will open and hopefully the gas will be lit by the HSI. The gas valve does not care whether the HSI worked or not. There is no check by the board to test the HSI while it is operating. Once the gas valve has opened the flame rod sensor has about 2 seconds to prove there has been ignition or not. If not the board will shut off gas valve and start sequence over again. After 3 tries it will lock out the furnace and throw a code.

The HSI is really the dummy in the equation, the board doesn't care or check whether it works or not. It has nothing to do with nothing. :)


thanks for the info man that helps me out.

[tinknocker service tech]

with these new ignitors the voltage to them drops to the point where they wont lite to burners then on the next try the voltage is increased to the last recorded voltage the burners lit and remain there till the power is disconnected the starts the search orver again

it is possible the valve is slow to open and not lite but not likely
the board doesnt care if the ignitor isnt hot enough it just times it

there is something else happening on this unit and time for your tech to become a tech and stop changing parts

[ZZZRSC]

The gas valve does not care whether the HSI worked or not. There is no check by the board to test the HSI while it is operating.

The gas valve doesn't care, but I know of at least one control board that does. It was on a commercial boiler though. A "senior tech" with any knowledge at all wouldn't put in a third gas valve, as the likelyhood of the first two being bad is pretty slim. If there is a drain pressure switch, it has to be closed at this point to allow board voltage to the gas valve, otherwise make the following test: You should have a voltmeter on the gas valve terminals and a pressure gauge on the test port; it should have made up to three 8 second attempts to open to allow the burners to fire. If it opened and the pressure (3.5") was there, the burner should have lit o.k.
Above all let us know what you find, as sequence of operations are always changing.

[stvc]

A good tech will, before comdemning the gas valve, check for voltage to the gas valve. In a situation like you've described, I'd run it through a cycle and check when power if applied to the gas valve, all the while watching the igniter to see when it drops out. If the igniter is a silicon nitride unit, the frequency to the igniter might be too low, thus causing the problem. My first inclination would be to check with the manufacturer if I don't have the cycle specs at hand. It could be a bad board but it could also be interference from some other electrical source. As an example of how extreme those problems can be, our company once followed the manufacturer's specs exactly, including installing electrical filters on the incoming electics, replace wiring harnesses, gas valve, control board, igniter and finally, the whole darned furnace!!!! Still had the same problem. Factory finally said, switch the phases on the unit. We switched it at the C/B panel and the problem went away. This was in a very small U.S. Post Office and apparently there was some postal equipment creating electrical noises that affected the main control board. In that case, the SiN igniter received a different frequency through each start cycle, each one less than the previous one until the furnace wouldn't light. The control was then supposed to do a purge and then step the frequency back up to the last level that lit the fire. Unfortunately, with the electrical noise it was receiving, the control would just go into a lockout mode. So knowing the manfucature's specs is hugely important these days. Guess work is a thing of the past.

Just curious, electrical is one of my favorites.
Was this a single phase or 3 phase system?
120 or 208/240V ?

[jibroni69]

I have never seen a variable voltage ignitor? If you decrease the voltage and the resistance of the HSI remains the same, the amperage would increase. There would be no savings in that. Who uses these? every residential brand of gas furnace I know of uses a straight up 120 v HSI, not sure about those stupid honeywell smart valves though. Enlighten me plz, i appreciate it

[stvc]

I have never seen a variable voltage ignitor? If you decrease the voltage and the resistance of the HSI remains the same, the amperage would increase. There would be no savings in that. Who uses these? every residential brand of gas furnace I know of uses a straight up 120 v HSI, not sure about those stupid honeywell smart valves though. Enlighten me plz, i appreciate it

I think you might be responding to my post but am not really sure.
My question to skippedover about the incoming electrical service, phase and the operating voltage of the equipment had more to do with what the source of that problem really was, rather than the equipment itself. Electronic equipment does strange things to the sine wave and can't be measured without a true RMS meter. In a perfect world if you have a single or 3 phase system with a balanced load on all phases neutral current will be 0. When you add a buch of electronic loads to the system the power supplies in them clip the sine waves and balance becomes distorted. It does strange things. A non true RMS meter may read zero on a neutral conductor but a true RMS meter could read 500 Amps. That is why neutral conductors of multi wire systems burn up in commercial sytems. I think it may also be migrating to residential systems along with other problems.

[ZZZRSC]

I think jibroni was refering to TinKnocker's statement "with these new ignitors the voltage to them drops to the point where they wont lite to burners then on the next try the voltage is increased to the last recorded voltage the burners lit and remain there till the power is disconnected the starts the search orver again"
I have never heard of this response, but there are a lot things I haven't heard of. Also, if you reduce the voltage to an electric heater (ignitor) the amperage and wattage will decrease I=V/R and W=VxI where R is a fixed value for the ignitor. This is not true for an electric motor.

[Airmechanical]

Strange, sounds more like the time delay built into the board is malfunctioning, check the HSI for voltage and exactly when the 120v is dropped from the HSI. I suspect the board is dropping the HSI too quickly, it cools a bit and the gas valve opens. These are 18 second HSI's are they not? Double check the sequence of operations on this particular model and time when the gas valve cuts in, also check the voltage at the gas valve, weak voltage could account for valve opening late. Could be a number of things , but resistance means nothing on this one.


agreed;

that is right where i would of started, (unplug the ignitor check voltage and timing voltage was applied and disengaged)

also as others have stated, it is easy enough to change every part in the unit

but why not just use your meter to diagnose the part you are thinking of changing

in this trade (servicework) when performed properly, parts are checked then if proven faulty (with a meter) parts are changed!



.

[hvactech1jm]

The gas valve does not care whether the HSI worked or not. There is no check by the board to test the HSI while it is operating.

The gas valve doesn't care, but I know of at least one control board that does. It was on a commercial boiler though. A "senior tech" with any knowledge at all wouldn't put in a third gas valve, as the likelyhood of the first two being bad is pretty slim. If there is a drain pressure switch, it has to be closed at this point to allow board voltage to the gas valve, otherwise replace the integrated furnace control board. You should have a voltmeter on the gas valve terminals and a pressure gauge on the test port; it should have made four 8 second attempts to open to allow the burners to fire. If it opened and the pressure (3.5") was there, the burner should have lit o.k.
Above all let us know what you find, as sequence of operations are always changing.


yea thats what i was getting at why would a senior tech try 2 gas valves an still think thats what it is i mean what are the odds of getting 2 or 3 bad valves that do the same thing. thanks ill let ya no what happens.

[beenthere]

A manometer would be a help when doing a dianostic on this.

[Milk man]

need to give this guy a break. Because you are showing your ignorance as how some other equipment works. And some of you should know better.

My gas oven's HSI has to draw a minimum amount of amps before the gas valve to open and stay open.

[Milk man]

Goodman and maybe Lennox used an igniter and board that reduced voltage to the point the furnace would not light. Then on the next attempt the voltage was increased to the last ignition point. (As stated above)

[Airmechanical]

need to give this guy a break. Because you are showing your ignorance as how some other equipment works. And some of you should know better.

My gas oven's HSI has to draw a minimum amount of amps before the gas valve to open and stay open.

yap, and on the space shuttle before ignition takes place..........:D:p



.

[erc tech]

This is most likely not the problem, But get the senor tech to check the condensate piping on this 90%er. if its not draining correct it will try and fire up by sputtering popping but the second pressure switch will not make. Also check the green gound wire that runs behind and routed back of the inducer housing. Its close to the heatexchanger box and I have found them badly burnt giving the gas valve a fit

[Milk man]

yap, and on the space shuttle before ignition takes place..........:D:p



.

Are you sure they don't have a three tries for ignition before a soft lockout?:D

"Houston, we have a problem"
"Houston, the damn thing locked out again"
"Houston, I turned the key off and back on, it should light now. We can check the problem after the mission, during regular business hours."

[tinknocker service tech]

first i take it this is a new furnace
with these newer boards and ignitors the board does reat the ignitor
in some cases
some of the WR boards if you unplug the ignitor to test to see if voltage is been applied or when it is turned of the board will go into default and show ignito fault

you need to check the voltage at the board with every thing intacted

again is it propane or natral gas and what is the manifold pressure
is the ignitor lined up properly and are the burners clear and lined up

after te third valve what did he want to change next

if this is an older unit it may have a weak ignitor or the wrong one
amping the ignitor will give this info. If 3.0 or higher it is good, if less then 3 then time for a new one even if 2.99 it needs to be replace

being you are new then just kick back and watch. ask questions and learn
he isnt going to listen to you from what you are saying here

apply for pro menbership so you can realy learn things the correct way because there is a lot of good info there that cant be posted here

[hvactech1jm]

need to give this guy a break. Because you are showing your ignorance as how some other equipment works. And some of you should know better.

My gas oven's HSI has to draw a minimum amount of amps before the gas valve to open and stay open.

yea this is what im talking about i new some equipment did this. that shows what some of the other guys on here no. thaks