ReplyIn what way exactly?
Originally Posted by pecmsg
Membership Chair/ARP Committee / Professional Member*
The original installer probably adjusted the burner input to better match the furnace with the house 36 years ago. Which used to be a somewhat common practice. Any chance the original manual is there somewhere near the furnace? I always leave them on furnace installs and it may well detail the capacity reduction procedure. The gas pressure reduction was probably a part of the capacity-to-space adjustment of the furnace as well.
Ignition delay / poor flame propagation often results from corrosion, and/or accumulated dust/dirt - something which any truly thorough inspection and cleaning would have remedied.
If the original install ran well for 36 years - was then changed and the furnace subsequently exibited adverse symptoms - it seems reasonable to project that the changes were the genesis of the adverse situation.
What was the gas pressure turned up TO?
What is the gas pressure supposed to be? And how do we know that?
Ws the heat exchanger examined with a camera or otherwise?
Was any combustion analysis done?
Was the temperature rise checked and found to be within the furnace's rated range?
PHM
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PHM
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When faced with the choice between changing one's mind, and proving that there is no need to do so, most tend to get busy on the proof.
Membership Chair/ARP Committee / Professional Member*
In what way exactly?
PHM
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When faced with the choice between changing one's mind, and proving that there is no need to do so, most tend to get busy on the proof.
Membership Chair/ARP Committee / Professional Member*
Whew!
PHM
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When faced with the choice between changing one's mind, and proving that there is no need to do so, most tend to get busy on the proof.
Regular Guest
Thank you for understanding my situation. I am concerned with safety and want to know if turning up the gas pressure is causing the furnace to overheat.
Professional Member*
I agree with PHM on this one.
You didn't have a problem until someone messed with it, at least not performance wise. Sure, you could replace it, but I doubt it's necessary to get it working like it was.
I don't think that having a capped burner and then turning the gas pressure down makes a lot of sense, if you have a pipe with a certain amount of flow, you then cap one, then you adjust it to be 3.3" or whatever it is on furnaces, but it's adjusted that way AFTER the pipe was capped.
If you took the burner and capped it without adjusting gas pressure after, you would have excessive gas, but that obviously wasn't the case here since it worked fine for ages and then someone messed with it.
In theory, excessive gas CAN cause an overheat if there is EXCESSIVE gas, as in the tech turned it above the manufacturers recommendation, but otherwise it shouldn't. Considering that you didn't have a problem until it was turned up, I would just turn it back down to where it was or actually find out why it's overheating if the gas pressure is at the right setting.
Professional Member*
In short it seems like it is.
That furnace setup is not unusual at all for the time it was installed. If the airflow is low as suspected, temp rise was probably used to set the manifold pressure after the burner was plugged. As long as the heat exchanger is intact, it is safe to operate if setup properly again.
Professional Member*
What brand, and model/serial is this furnace if any of those labels are legible? I have seen many brand new furnaces that have burner orifices capped from the factory. It’s not guaranteed that a technician changed the original design. Does your furnace have 1 motor only in it, to circulate the air in your home? Or is there another smaller motor towards the top that looks like part of the flue/chimney part? I’d guess your furnace is natural draft (only 1 motor) and could be as low as 60% efficiency. The minimum efficiency of current furnaces is 81%. Depending on your location/climate your contractor may recommend a high efficiency furnace up to 98%. A plastic smell could indicate a serious issue and should be investigated to resolution. Be very careful running your furnace. Please invest in a low level CO monitor.
There are two ways to do things, Right and Again.
Professional Member*
I am pretty sure we are dealing with a 3wire pilot and they do get flaky, but they usually always take some time to get warm enough to turn on the gas valve. It is when the gas valve/burners turn on and off or chatters that your looking at a failing 3 wire pilot assembly, so you probably paid out for something you did not need there. Newer techs find those earlier 3 wire pilot systems a curiosity and more often than not mis-diagnose them.
Those older CES0110 carrier control boards with the ice-cube relays need a kick in the butt to get the blower relay to engage sometimes, but that only verifies it is time to replace the board due to the failing relay that the tech said he had to tap on to get working.
SO I have a feeling that the board is failing, preventing the blower from operating properly or timely, two speed blower maybe and running at wrong speed, thus furnace overheating, getting nasty hot acrid smell. I have a feeling that dialing up the gas pressure is not going to make a huge difference in the temperature rise, but if the company did perform a true PM, they should have listed down the manufacture's listed "Temperature Rise" which is required to be listed on a furnace data plate/sticker by law. Then taken measurments of what the temperature rise is across the furnace versus what is listed and written down their findings. Temperature Rise is probably the number one thing any tech should take and record. This will dictate what the next step of the service visit will be. If the temperature rise is excessive or high, then I would be looking at static pressure, filters, AC coil, blower wheel, blower performance, gas pressure, etc.
Right now it seems like a monkey poop fight and your not getting the specifics you need to make an educated decision on what to do and with your inability to supply us with that data, we are useless to assist you. All we can do is bicker amongst ourselves and utilize personal experience and opinions to blindly help you.
Get us the model number of the furnace, does it have an AC coil?
Get us the actual numbers from the service tech's visit, we need listed temperature rise, actual measured temperature rise, original gas pressure versus adjusted gas pressure setting. Blower listed amps versus actual running amps. Numbers don't lie.
Good luck and Happy Thanksgiving
Professional Member*
Doubtful...
Turning up the gp a couple 10ths of an inch didn’t create all of these issues.
Did older “RGGED” furnaces work for years? Absolutely yes, but it’s very highly unlikely that a combustion analysis was performed. Remember this was back before the days of the electronic CA. We had a chemistry set in order to do it, and if your company performed this test routinely on any and all equipment modifications you’re one in a million.
Just because “old school” modifications worked didn’t mean they were efficient and or safe. It just means they allowed the furnace to run. The longevity has nothing to do with the techs mods. It had to do with the durability of the equipment.
When the introduction of redundant safety controls were adopted as a standard, techs could no longer perform these “old school” mods. Manufacturer specs became much tighter and there was less room for alterations. I’m sure cavemen were able to get really good fires going until they figured out it could kill them... Hmmmmm, I wonder why redundant safety controls were adopted as a standard?
Last edited by mgenius33; 11-29-2019 at 09:29 AM.
"The only true wisdom is in knowing you know nothing" Socrates
Professional Member*
Sure, but was it going off on overheat until someone messed with it? No.
I'm sure any of us could walk in anywhere and find some problem with some unit, small or big, that's what we do.
Professional Member*
I would doubt that turning up the gas pressure from 3.2 to 3.5 made a huge difference on temp rise. It is more likely that the furnace had air flow issues before this was done and the added gas just compounded the issue. I don't think the added gas pressure caused the smell or the board malfunction although it is a slight possibility. Since it was said that the heat run are buried under insulation I have to assume that the furnace is in a horizontal configuration. In this orientation it is possible for heat to travel into the blower/control section of the furnace while the blower is off and cause an overheating of the controls. This is usually caused by an obstruction to air flow like a dirty A/C coil mounted after the furnace which would also be a likely cause for the limit opening.
The bottom line is you may not need a new furnace but it may be less expensive in the long run to cut your losses and change it rather than put more money into it only to find another problem later. If you should decide to have the unit replaced make sure that they do a load calc {Manual J} to properly size the new equipment. From the way you are talking it sounds like even with one burner inactive your furnace is still too big.
Regular Guest
I can get those numbers. The pilot lights the burners for seconds and are now turning off once or twice before actually staying on as they should. The tech says it is a slow moving gas valve. Not sure what that means.
To answer previous questions:. The furnace is vertical. Heat runs are in the attic. Yes AC coils.
Last edited by Warmest; 12-05-2019 at 09:04 AM. Reason: Add info
Professional Member*
Means hes Full of it!
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Regular Guest
Tell me more. I need info to call him on his BS.
Professional Member*
Tell him to get the documents on your slow moving gas valve...………………….
Better to just give up and find a different contractor!
R I P Icemeister
Supporting our Vet’s
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Professional Member*
Not necessarily. Some Carrier/Bryant furnaces did have a slow opening gas valve. However if the furnace has a 3 wire pilot it sounds more like the pilot switch is opening and closing at start up as I believe was mentioned before.
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