# Noritz heat exchanger



## sikxsevn

I'm posting this because this is bothering me. I went on a warranty on a 5 year old noritz N-084M last night that the outside of the heat exchanger was corroded so horribly that it wouldn't let air through it. I replaced the heat exchanger, and adjusted the fan speed, but the combustion chamber temps are still a little high, around 700-775 degrees F. Shouldn't it be more in the 550-600 range?

The unit is properly installed, with a fairly short venting run, and it does have the drip tee installed in the vent according to manufacturers specs. 

My main question is this: what caused the heat exchanger to corrode like it did?


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## sikxsevn

I should also note that before it was getting up to around 900 and then shutting down and throwing a code 90. The fan speed correction would get to 110, even after replacing the fan and adjusting the base speed. I pulled off vent and looked up it, no obstructions, and the vent cap was still on. But when I looked down into the exhaust on the heater, solid green. 

As noted before, at it's hottest it now runs 700-775, and the fan speed correction is at 104% instead of at 110% from before. Also of note is that the heater is located in a hot attic (it was 137F when I got there) with limited ventilation. The incoming water is 80F and the heater is set on 115F, only a 35F rise. The hottest the tankless gets is between 1.8 and 3.2 gpm, it runs much cooler at 5.0+ gpm, down in the low 600s. Below 1.8 gpm, the heater runs in the high 600s.


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## Redwood

90 code is poor combustion...

Gas Pressure?
Blow out the dirt...
Has it been descaled?


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## sikxsevn

Not to argue, but in my service manual the wording is "abnormal combustion."

Manifold pressure was in range, and the inside of the heat exchanger was descaled, it was the outside that was deemed uncleanable and noritz sent a new one that I installed. The house it self is fairly new, about 10 years old

Also, the first day I was out there I took the gas valve off and then blew everything out with an air compressor, per tech support instructions


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## SewerRatz

I would look into combustion air. Many areas I have seen poor air quality ( grease, aerosols, dust, lack of oxygen) cause the heat exchangers to corrode externally. This is why i always talk the people that are insistent on getting a tankless water heater to get one that uses a direct vent system, this way it gets its combustion air from outside.

You can get the abnormal combustion due to poor combustion air quality.


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## Redwood

sikxsevn said:


> Not to argue, but in my service manual the wording is "abnormal combustion."


Poor or, Abnormal....

It Ain't Right! That's for sure... :laughing:


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## OldSchool

Lots of thing can cause incomplete combustion..

- blocked venting
- gas pressure
- primary air 
- secondary air
- dirty burner
- inducer fan or ventor motor
- regulator
- undersized gas lines

Once you check all of those and it checks out ... it could be one of your fan motor do not have the proper RPM.


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## OldSchool

As for excessive air temp in venting

- To much induced draft
- to high fuel pressure
- corroded or scaled or blocked up heat exchanger


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## Tankless

sikxsevn said:


> My main question is this: what caused the heat exchanger to corrode like it did?


To answer ur question........condensation. if you look down the "flue collar" to the top of the exchanger and it's green that's the condensate. You mentioned there was a drip tee.....i have seen on more then one occasion guys put in a horizontal dtv-4 in a vertical position and vice versa.

If you have the correct tee in place. I would look at your air make up.......as i teach NY clients....its not just air make up....it's clean air make up. That's what killed ur exchanger....insulation....dust....poor clean air make up are all red flags for issues. You will be doing this job again. I just pulled an 8.4m and did two nr 83's dvc....with a new softener. It had to be done to give these people a reliable heating system. The dust gums up the exchanger....less air flow and now a concentration of heat to throw temps all over the place.

As for your combustion temps....i font have the figures near me but you should not ever be adjusting fan speeds unless your at 4000 ft. Or higher. Something else is going on....but poor make up will not cause that severe of a restriction unless you got no air coming in. 

And the internal Mani pressures should not be close....whey should be right on within a half inch. Sometimes i take the high down a half when a heater is grumbling...but no more then that. 

All's i can tell you is if you give the heater what it wants it will operate correctly....barring the occasional doa.


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## sikxsevn

Thank you for the advice, if I have to go back out there we may swap it out for a DV unit, and I'll be sure to look into how little ventilation that attic has, that may be the source of the problem


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## breid1903

hey, i've been poor AND abnormal all my life. breid................:rockon:


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