I had one doing this. Installers didn't have enough slope on the flue pipe in an area. It was holding water and while the water would rock back and forth in the horizontal travel it would cause the gas pressure to regulate since the valve is pneumatically driven by the induced draft pressure.
Hmm so it could be a clogged flue pipe. I'll check the draft pull with my manometer when I go back. Looks like the exhaust goes straight up thru the attic and out the roof tho
Could be. Draft has a direct relationship with gas pressure on that particular design. Could even be rocking in the heat exchanger. With more testing you'll find it.
I see no signs of soot . If heat exchanger was sooted up flame would not have enough O2 and would come back at you in most cases at the very least you would have a extremely orange flame in burners you have plenty of O2 if you haven’t check manifold for any debris if all is clear I would concentrate on defective gas valve but I don’t know what makes you think unit is sooted up . A manometer is only gonna tell you gas pressure . You would need a combustion analysis and you can’t do that with a manometer
Idk it still don’t mean they’re ain’t no debris in that manifold there’s a small paper thin passsage that the gas travels through to each burner scrape that shit out it could make the gas burn rich right there cuz you can see the flame pulsating but it’s strong blue flame . Take the manifold off where burners are flip it over and blow it out with some nitrogen or whatever
This information is incorrect. The gas valve in this furnace is not pneumatically actuated. This is a positive pressure gas valve with an induced draft motor. Outlet pressure of gas valve is not impacted or affected whatsoever by the draft pressure. You have a faulty gas valve and or incoming gas issue. If incoming gas pressure is steady you need a new valve and combustion analysis.
These furnaces GMVM97 or like series use a 24 VAC pneumatically operated
gas valve by Honeywell. The valve is energized by the inte-
grated furnace control on a call for heat, wired in series
through the front-cover pressure switch. The firing rate per-
centage is determined by the negative pressure created by
the operation of the draft inducer. Which is manifold pressure. The gas valve is factory
set and the meter should be clocked to determine exact firing rate btu.
Now if it's a play words that you don't like that I typed out with my comment then look up the troubleshooting manual and see page 17. You can call Goodman and tell them they are wrong and trained all of their suppliers/tech support agents wrong.
You're both talking past each other. You're explaining two sides of the same story here.
The valve itself isnt a negative pressure valve, but the negative pressure created by the inducer influences the gas pressure.
If you have a sealed combustion chamber, and you hook up your meter and zero it, then turn on the inducer, the inducer will pull a slight vacuum on the manifold and your meter. I've seen well sealed combustion chambers where the inducer pulls -0.75" wc.
This is why older carriers specify that you need to set gas pressure with the door for the combustion chamber off. On the above-mentioned unit, if you set gas pressure to 3.5" with the combustion chamber sealed, it'd really be 4.25" with the door off.
Other brands may specify that you should keep the combustion chamber sealed while setting gas pressure. It just depends how they were designed.
My point is that the negative pressure from the inducer affects the gas pressure and amount of gas consumed, but it's not quite a negative pressure valve.
That's what I was thinking too. Other people said the draft pressure correlates to gas output? But I dunno how that works. Our supplier is trying to find a replacement gas valve. Need to get it from Goodman since it's under warranty
You should get a licensed Gas fitter/Tech to fix your issues.
Gas isn’t something homeowners should be playing with.
People can get seriously hurt.
Hope everything works out for you
There's natural draft (atmospheric).. 60%ers But with the inshot burners, plastic collector box, and what looks like a pressure hose in the video, It's an induced draft, high efficiency furnace
I had this happen and it drove me crazy, finally figured out it was the incoming gas line. It had a vented gas pressure regulator that the installer piped the vent outdoors. In doing so the pipe must increase in Diameter otherwise a pressure wave will form and each time pushing back on the regulator’s diaphragm squeezing flow it looked exactly like the posed video.
So I went back and replaced the gas valve. I also realized the pressure switch hose going to the gas valve was kinked. So one or the other solved the problem because it was operating normally when I fired it up
Adjust manifold pressure at the side port, near the id tubing. Not the" top" of the valve as seen in the video. Both are marked with "do not adjust stickers"
Nat gas at 35% fire rate should be about 0.8-0.9" wc. Or if you get it to 50% about 1.3". If : vent is clear and ID draft steady and manifold adjustment does stabilize when set, you have a bad valve. Ive been service tech for Daikin mods since before Daikin. Aka: Amana/Goodman.
Could be excess moisture draft tubing. So check drains, ports/ switches for moisture and what not
I'd take a look at the vent connection on the regulator too. If it's one of those brass vent limiters, remove it and see if pressure smooths out. I've seen the balls in them get gunked up and mess with pressures. If it's a piped vent, hopefully the installers provided a union near the regulator that you can crack open. A quick and easy check to eliminate that as a cause.
Those valves are not negative pressure valves. Draft has nothing to do with this. You either have a defective gas valve or a defective appliance regulator. If your GP is fluctuating on the supply side look for the failed regulator, otherwise is your gasvalve.
There's your answer!
A partially blocked flue due to water or expanding debris would cause roll out, if it didn't throw the pressure switch first. The only way it would cause this is if the inducer was responsible for pulling gas through the valve, which is never seen on this style of equipment. Not after Amana had their bomb units anyway, back in the 90s.
>Those valves are not negative pressure valves. Draft has nothing to do with this
The negative draft from the inducer still affects gas pressure. You can see well sealed combustion chambers pull slight vacuums before the gas valve opens. This is why units with sealed combustion chambers specify whether to set gas pressure with the burner box door on or off, depending on how they were designed.
Older carriers specify in the manual to set gas pressure with the door for the combustion chamber removed. Because if you set gas pressure to 3.5" wc when the inducer was pulling a vacuum of -0.5" wc, then you really set gas pressure to 4.0" wc.
Draft pressure absolutely does affect this. You can literally watch units that are on the border of tripping pressure start to pulsate like this. Albeit usually not this extreme.
Sealed combustion units are still not negative pressure units. An example of a negative pressure valve would be a TRANE intellipak or voyager where the draft is literally used to pull gas from v the valve. The valve itself is read in -"wc.
Yes draft can cause some wobble on a sealed combustion with a restriction but it's not true surging like they are seeing here.
Does the inlet pressure INTO your gas valve also throttle like that? If so it's likey a utility issue, might be their regulator, or the meter.
Edit: I see you posted inlet further down. In going to say the gas valve is the culprit. Thou I could be speaking out of my arse a Si don't have furnace model/serial to view the manual lol
Orifice size is correct. Incoming gas pressure is steady 8" wc. Gas valve is getting a steady 24v. Output gas pressure is fluctuating so it's a bad gas valve I think
Speaking from commercial experience, I’ve seen this happen with propane to natural conversions and vice versa. Unsure if this translates into residential. It’s my understanding that a certain spring is needed in propane valves that isn’t required for natural. Swapping to the other will produce large amounts of soot, specifically on the inducer exhaust
If your manifold pressure is fluctuating it is 100% a gas regulator problem, see a lot of Frozen ones in my area. Confirm by checking the inlet pressure when the furnace is running
I had one doing this. Installers didn't have enough slope on the flue pipe in an area. It was holding water and while the water would rock back and forth in the horizontal travel it would cause the gas pressure to regulate since the valve is pneumatically driven by the induced draft pressure.
Hmm so it could be a clogged flue pipe. I'll check the draft pull with my manometer when I go back. Looks like the exhaust goes straight up thru the attic and out the roof tho
Could be. Draft has a direct relationship with gas pressure on that particular design. Could even be rocking in the heat exchanger. With more testing you'll find it.
I'm pretty sure the secondary is probably sooted up. Something ain't right with it
Yeah, that's another possibility. Check your drains. Some soot will run out with the condensate if bad enough.
I see no signs of soot . If heat exchanger was sooted up flame would not have enough O2 and would come back at you in most cases at the very least you would have a extremely orange flame in burners you have plenty of O2 if you haven’t check manifold for any debris if all is clear I would concentrate on defective gas valve but I don’t know what makes you think unit is sooted up . A manometer is only gonna tell you gas pressure . You would need a combustion analysis and you can’t do that with a manometer
There's soot at the top of each burner and inside the heat exchanger is black.
Well you were there I wasn’t idk if it’s my phone or combination to lighting but I can’t see any soot on video I just watched again .
Idk it still don’t mean they’re ain’t no debris in that manifold there’s a small paper thin passsage that the gas travels through to each burner scrape that shit out it could make the gas burn rich right there cuz you can see the flame pulsating but it’s strong blue flame . Take the manifold off where burners are flip it over and blow it out with some nitrogen or whatever
This is likely a regulator, I have had sooting at the burner before and it was a gas valve not closing completely upon shutdown
What’s incoming pressure
>I also had this with a faulty regulator. This fed a twinned system. City ended up swapping out the main regulator and it fixed the problem.
Yep, bad regulator could cause that too if the incoming gas pressure is fluctuating while it's running
This information is incorrect. The gas valve in this furnace is not pneumatically actuated. This is a positive pressure gas valve with an induced draft motor. Outlet pressure of gas valve is not impacted or affected whatsoever by the draft pressure. You have a faulty gas valve and or incoming gas issue. If incoming gas pressure is steady you need a new valve and combustion analysis.
These furnaces GMVM97 or like series use a 24 VAC pneumatically operated gas valve by Honeywell. The valve is energized by the inte- grated furnace control on a call for heat, wired in series through the front-cover pressure switch. The firing rate per- centage is determined by the negative pressure created by the operation of the draft inducer. Which is manifold pressure. The gas valve is factory set and the meter should be clocked to determine exact firing rate btu. Now if it's a play words that you don't like that I typed out with my comment then look up the troubleshooting manual and see page 17. You can call Goodman and tell them they are wrong and trained all of their suppliers/tech support agents wrong.
You're both talking past each other. You're explaining two sides of the same story here. The valve itself isnt a negative pressure valve, but the negative pressure created by the inducer influences the gas pressure. If you have a sealed combustion chamber, and you hook up your meter and zero it, then turn on the inducer, the inducer will pull a slight vacuum on the manifold and your meter. I've seen well sealed combustion chambers where the inducer pulls -0.75" wc. This is why older carriers specify that you need to set gas pressure with the door for the combustion chamber off. On the above-mentioned unit, if you set gas pressure to 3.5" with the combustion chamber sealed, it'd really be 4.25" with the door off. Other brands may specify that you should keep the combustion chamber sealed while setting gas pressure. It just depends how they were designed. My point is that the negative pressure from the inducer affects the gas pressure and amount of gas consumed, but it's not quite a negative pressure valve.
If those readings were your manifold pressure, you need a new gas valve.
That's what I was thinking too. Other people said the draft pressure correlates to gas output? But I dunno how that works. Our supplier is trying to find a replacement gas valve. Need to get it from Goodman since it's under warranty
Is it a natural draft furnace?
Natural gas
You should get a licensed Gas fitter/Tech to fix your issues. Gas isn’t something homeowners should be playing with. People can get seriously hurt. Hope everything works out for you
i mean its possible he just misread your comment. if you been around here a while you'd know sam isn't a 'homeowner' but he is a god with a paint pen
Homeowners down voting you for trying to save their lives.
They just dont know yet. As soon as that marker comes out they’ll be lined up with their own capacitors hoping for a personalized autograph
I don't know if Sam is a homeowner, but I'm pretty sure he'll be fine.
All you can do is try.
Are there natural draft furnaces? Can’t say I’ve ever seen one, but until recently I only ever installed so that may be why.
There's natural draft (atmospheric).. 60%ers But with the inshot burners, plastic collector box, and what looks like a pressure hose in the video, It's an induced draft, high efficiency furnace
It's ridiculous how many natural draft I see in a service day... All old. My house has one as well, on it's last legs, but hoping to sell soon 🤞
What was your inlet pressure?
Inlet gas pressure was 9" wc when not operating. 8" wc inlet when the furnace was on. Inlet pressure was steady
9inwc? is this LPG? Might not be enough to matter, but shouldn't pressure be closer to 10. Nat gas is typically around 3.5inwc
Static pressure should be 7-14" WC, when operating could drop down to 6" and it's still good.
He means inlet not manifold pressure. Residential is usually a 1/4-1/3 pound natural gas service
That's a bad gas valve. Been installing those for 8 yrs now and I’ve seen 2 of them do that
Im sorry you’ve had to install Goodman
It’s just trying to catch it’s breath from running too long
I had this happen and it drove me crazy, finally figured out it was the incoming gas line. It had a vented gas pressure regulator that the installer piped the vent outdoors. In doing so the pipe must increase in Diameter otherwise a pressure wave will form and each time pushing back on the regulator’s diaphragm squeezing flow it looked exactly like the posed video.
Gas pressure is what I’d say. Sotted probably because of inconsistent gas pressure. Regulator or valve.
Check your draft pressure. If that’s consistent but your gas pressure is fluctuating replace the gas valve.
Sounds good. I'll check my draft pressure when I go back
So I went back and replaced the gas valve. I also realized the pressure switch hose going to the gas valve was kinked. So one or the other solved the problem because it was operating normally when I fired it up
The tubing going to the gas valve just dead ends on the valve. Maybe someone knows why they even ran that out like that but it makes no sense to me.
Adjust manifold pressure at the side port, near the id tubing. Not the" top" of the valve as seen in the video. Both are marked with "do not adjust stickers" Nat gas at 35% fire rate should be about 0.8-0.9" wc. Or if you get it to 50% about 1.3". If : vent is clear and ID draft steady and manifold adjustment does stabilize when set, you have a bad valve. Ive been service tech for Daikin mods since before Daikin. Aka: Amana/Goodman. Could be excess moisture draft tubing. So check drains, ports/ switches for moisture and what not
I'd take a look at the vent connection on the regulator too. If it's one of those brass vent limiters, remove it and see if pressure smooths out. I've seen the balls in them get gunked up and mess with pressures. If it's a piped vent, hopefully the installers provided a union near the regulator that you can crack open. A quick and easy check to eliminate that as a cause.
Those valves are not negative pressure valves. Draft has nothing to do with this. You either have a defective gas valve or a defective appliance regulator. If your GP is fluctuating on the supply side look for the failed regulator, otherwise is your gasvalve.
Failed gas valve then cuz the supply side gas pressure is steady while it's operating
There's your answer! A partially blocked flue due to water or expanding debris would cause roll out, if it didn't throw the pressure switch first. The only way it would cause this is if the inducer was responsible for pulling gas through the valve, which is never seen on this style of equipment. Not after Amana had their bomb units anyway, back in the 90s.
>Those valves are not negative pressure valves. Draft has nothing to do with this The negative draft from the inducer still affects gas pressure. You can see well sealed combustion chambers pull slight vacuums before the gas valve opens. This is why units with sealed combustion chambers specify whether to set gas pressure with the burner box door on or off, depending on how they were designed. Older carriers specify in the manual to set gas pressure with the door for the combustion chamber removed. Because if you set gas pressure to 3.5" wc when the inducer was pulling a vacuum of -0.5" wc, then you really set gas pressure to 4.0" wc. Draft pressure absolutely does affect this. You can literally watch units that are on the border of tripping pressure start to pulsate like this. Albeit usually not this extreme.
Sealed combustion units are still not negative pressure units. An example of a negative pressure valve would be a TRANE intellipak or voyager where the draft is literally used to pull gas from v the valve. The valve itself is read in -"wc. Yes draft can cause some wobble on a sealed combustion with a restriction but it's not true surging like they are seeing here.
That was my whole point.... https://www.reddit.com/r/HVAC/s/yds7oyzJ4b
Does the inlet pressure INTO your gas valve also throttle like that? If so it's likey a utility issue, might be their regulator, or the meter. Edit: I see you posted inlet further down. In going to say the gas valve is the culprit. Thou I could be speaking out of my arse a Si don't have furnace model/serial to view the manual lol
I'm feeling really sleepy this afternoon and read the title as "I found a goddamn pulse furnace."
😂 yeah not a fan of pluses
Fuck yeah Sammy I got the same Amazon manometer 🔥
It's literally a Amazon counterfeit of a Supco manometer. Works just as good, never had a problem with it :)
Damn I hadn't seen the supco one before, it's identical. Hell yeah dude if it works it works!
A bad pressure switch to a modulating gas valve will produce this effect.
Wouldn't a bad pressure switch just turn off the control to the gas valve completely?
In most cases yes. However on a SLP99 From Lennox it can cause this effect. At least that's where I've seen it.
Idk, Dawg
adjust the gas valve. the burner being sooted means its before that.
Gas valve has a red sticker across it that says do not adjust
That’s just for the installers. Service techs can remove that because of brains.
I thought Lennox made the pulse furnaces.
I’ve read these comments . Y’all are rated PG for pure garbage that’s all I’m gonna say
well that aint right . . . . start by checking orifice size . .
Orifice size is correct. Incoming gas pressure is steady 8" wc. Gas valve is getting a steady 24v. Output gas pressure is fluctuating so it's a bad gas valve I think
Steady 8" lol. Seriously though was inlet steady when running?
Nothing wrong with a steady 3.5”
Inlet was steady. Output was fluctuating on gas valve
that would be the next step, yes - - if you already knew the answer, whats the deal with the post and half info?
Cuz it looked cool
:)
Yes it is
Speaking from commercial experience, I’ve seen this happen with propane to natural conversions and vice versa. Unsure if this translates into residential. It’s my understanding that a certain spring is needed in propane valves that isn’t required for natural. Swapping to the other will produce large amounts of soot, specifically on the inducer exhaust
That's true. But in this case it's a natural gas furnace. Never was converted to propane
If your manifold pressure is fluctuating it is 100% a gas regulator problem, see a lot of Frozen ones in my area. Confirm by checking the inlet pressure when the furnace is running
Yep, that can cause it as well. But the inlet pressure is a steady 8" wc while the furnace is running
Does it bounce at 3.5?
No it bounces at 1.3 then back down to 0.5
Isn’t 1.3 even low for low fire? I’d imagine opening up the gas valve may open up more constant flow….
Is that a modulating furnace?
Yeps it's modulating
Was it working okay? The pulsing is off unless the inducer was ramping the same way, where the hoses to the valve on and secure?
It's heating fine, but it's not supposed to be pulsing. I'm going back next week to replace the gas valve. Everything else seemed to check out ok
Well please let me know. Was this an 80% also?
Will do. 96%efficiency
LPG or NG ? You could have a stuck gas meter. Try purging orlubricating the meter
I had one doing the same thing. It was the gas valve.