Are the burners staying on all the time, or are they cycling on the limits. Were they operating good at one time, if so when. Was any electrical work done on the building where the phases could of been changed and the blowers are running backwards.
The burners are staying on the whole time. They are on a door switch where when they open a roll up door the units shut down and once it is closed the units start back up... Sometimes (probably about once every week or once every two weeks) we will have to reset the units in order for them to fire again. They were installed when the building was built around seven years ago and worked perfect for the first two heating seasons then they started getting worse and worse every year since then. The blowers are not running backward. The air is definitely blowing out at high volume. The blowers are operated by a VFD which can be controlled. About three years ago they had a company come in and install a/c coils to each of the units and they did it by removing the units from the wall, moving the structural steel that the units were mounted to (because with the new coil box for the a/c the unit would be in the way of the crane located in the building) and then the units were mounted back on the walk and ran the same as they did before the a/c was installed. This is just all hearsay because neither I nor my coworker have worked on the site at the time it was happening. We started and then the guys that took care of the site before retired shortly after. They didn't seem like they were worried about it because they were retiring but now we are stuck with the problems of these units.
Have you checked what the main gas pressure is while the 3 units are running, and all of the heat stages on. I know you said 3.5 in.w.c.
Is that a sealed combustion system. If so what is the combustion air pressure and what is the draft pressure. Have you checked the design pressure for both.
There is a software that you have to plug a laptop into the board on the unit and you can read the rpm of the combustion blower and the percent of gas at all six stages. They are all where they are supposed to be. I am thinking that the heat exchanger might be getting clogged because of the draft reading of the flue and the lack of the transfer of heat from the heat exchanger. My coworker swears that it cannot be the heat exchanger being clogged because there was no black soot coming from the flue.
Yes it stays at the 3.5 " w.c. during all the stages
Yes it is a sealed combustion system and we have not checked the combustion air pressure. The draft pressure is around zero (I say "around" because it will fluctuate between a negative and positive draft pressure... That is why I think that the heat exchanger is constricted.
So how are you controlling draft and combustion pressure. Does the system have a power draft and combustion blower external to the Heater?
What are the actual readings of the draft and combustion air. Have you verified that the pressure readings are correct with say a magnehelic gauge. Does the controller use a pressure transducer for draft and combustion pressure, and if so have you checked that the pressure pick up tubes are installed correctly. Make sure that they have not been installed in a way that they are reading velocity.
So what is the manifold gas pressure on the units while running with all stages on?
You think that there is a restriction in the heat exchanger but if that's the case have you experienced any sort of high temperature limit failure or short cycling of the heat?
Try getting the airflow and input rates set correctly first, then recheck the draft pressure. I'll wager that it'll fall in line. IMO the units are over-fired and the airflow is set way too high. How did you go about measuring the manifold pressure?
Originally Posted by breegle1313
Didn't know they used to work properly .
as flange said ,,,possible heat exchanger issue .
Is it sooted inside ? It may not be restricted , soot will INSULATE and kill heat transfer.
That would explain high stack temp and low TR...
Can you pull the burner or exhaust and inspect?
We've covered a lot of ground here already ....do the math ,,your output is low for rated capacity
You are underfired. IMO
You have verified gas pressure .
And that it is calling for all stages
And combustion appears correct
Stack is hot , TR is low
Look at the internal heat exchanger and see if it's fouled..
Can you post a picture of the unit and heat section so we can understand what we are looking at for sure , or even a link to pictures of off ICE website.
Posted the above assuming you have a power burner.
Give us a photo...
Is it like this ?
I stand by my opinion that you are underfired . That what I come up with after interpreting the info provided
Either the burner is not set or controlling properly (underfired) or you are sorted (fired properly but insulated)
Are you taking gas pressure AFTER the modulating valve?
Wish I could lay hands or eyes on it .
There is a draft control on that system and if not set or working correctly there could be insufficient combustion air or draft. It is very likely that the ICE controller is compensating for inadequate combustion or lack of enough air. This will result in a lower gas output due to the control safety function.
The symptoms are clear that you are under firing but this is just a symptom to your problem.
What is the control voltage input signal while the heat is running and is it corresponding to the load correctly?
Troubleshooting is not part of the repair..................understand the symptom's and you will find a solution.
Is this unit is pulling 100% outside air?
Originally Posted by breegle1313
Are your AHU making up the exhaust air by bringing outdoor air back into the building??