AAON intermittent flame failures

[sigma]

The machines are MUA units model: RNA-0-16-C-8-DAAOA-DB3KO.
There are two spark ignition modules per unit:
They are Aaon P/N V57870, 1097-850 series direct spark igniter by UTEC.
When there is a flame failure, diagnostic light flushes 1 time which means “control in one hour lock out”.
After restarting the machine burners come on all the time. When nothing is done the module resets on its own ( I guess after one hour). I have never seen other faults like:
2 flushes- Pressure switch open with inducer on
3 flushes- Pressure switch closed with inducer off
4 flushes - Limit switch is open
5 flushes -False flame 1 hour lockout
Have anyone experienced this situation?

[thatguy]

Forgive me for my looking up the numbers...

Have you checked the flame rod if that is what it is using for flame verification? May be on the cusp of needing replacement or cleaning?

Also have to checked for proper flame at the burners? Could be a cracked HX, blocked flu or blocked up HX causing the flame to extinguish?


Sent from my iPhone using Tapatalk

[patpinet]

Corrosion on the ground wire of the Ignition control.
Ground wire is the one that read the flame signal and get it back to the Ignition control.
Have you measured uA reading on the flame rod?
Is the flame rod clean and in good shape?

[sigma]

I think that now I have a pretty good idea what is going on. I believe that flame goes out intermittently because modulating gas valves throttle down to much and either flame is to week to be in contact with flame rod or just simply gets blown away due to low velocity. I wish I had time to watch it and see the flame right before it goes off.
These intermittent failures were always happening on warmer days. Now when outside temperature dropped, burners fire without issues. I have to reed the manuals and see if lowest opening of valves can be increased.

[buford]

Checked gas pressure thru all operations?

[heatingman]

Does this unit modulate the heat?


Sent from my iPhone using Tapatalk

[sigma]

Gas pressure wasn't checked through the whole operation and yes, the unit modulate heat.

There are two stages of heat; two ignition modules, two heat exchangers and two modulating draft inducers.

First stage has two modulating gas valves and stage two - one modulating valve.

[71CHOPS]

have you checked it with a combustion analyzer?

[sigma]

I am in-house maintenance and we don't have combustion analyzer.

Let's assume that i would have an analyzer and readings were not up to par.

How one can change the fuel to air ratio in this Aaon? Opening of gas valves and speed of inducer fans is controlled by Modgas controller.

[Spitz]

I'd assume it's a Maxitrol. If so they are about the easiest valves to adjust. Check your heat exchangers.

Sent from my SM-G960U using Tapatalk

[patpinet]

Personally I wouldn't do the combustion analysis.
It's a atmospheric burner and there's not much you can do to adjust combustion.

Make sure you have the right manifold pressure at high fire.
Low fire should be around 0.5 in wc

[sigma]

Personally I wouldn't do the combustion analysis.
It's a atmospheric burner and there's not much you can do to adjust combustion.

Make sure you have the right manifold pressure at high fire.
Low fire should be around 0.5 in wc

I believe that this is the best next move. When I get chance I will do that and let you know what readings I had.

[Spitz]

It has a atmospheric burner???

Sent from my SM-G960U using Tapatalk

[gravity]

Personally I wouldn't do the combustion analysis.
It's a atmospheric burner and there's not much you can do to adjust combustion.

Make sure you have the right manifold pressure at high fire.
Low fire should be around 0.5 in wc

Dont listen to this guy.

Perform the combustion analysis.

There are ways to adjust


Sent from my iPhone using Tapatalk