Tankless flame failure

[PatrickTheDrummer]

I have a Bradford White 199,999 BTU propane tankless water on my house. It is the only gas appliance I have. It has worked for 7 years. Occasionally the water would go cold during a shower and I would have to turn the water off and back on to restart the heater. This may be a clue, but is not my current issue.

Recently my 250 gallon tank sprung a leak and had to be replaced. I had it replaced with a smaller 100 lb tank. The same regulator and plumbing are used on the new tank. The new setup worked fine the first day. That night the temperature dropped from 70 to 40. The water heater stopped working. If I go outside and turn on hot water I can hear the flame start, feel a short puff of warm air from the vent, then it goes cold and I get a code 12 (flame failure).

Yesterday my gas man came and turned the regulator up to put out 13.5 inches water column. This is as high as the regulator goes, and what the unit calls for. This solved the issue at the moment. It was 60 degrees outside. That night the temperature dropped back to 40 - flame failure again. Is it possible that my regulator is on the verge of going bad and the temperature drop with cold weather is messing with it?

 

[Fitter30]

Heater might have a inlet air filter just inside the cabinet thats dirty. Flame rod could be dirt and or the burner. Need complete model#.

 

[Sponsor]

 

[Bannerman]

With only a 100# tank, the liquid propane vaporization rate @40℉ is most likely below the BTUs needed by the tankless unit. A higher capacity regulator will not help when the quantity of vaporized fuel provided by the tank is insufficient. At 60℉, vaporization will be more rapid and sufficient to supply the BTUs required.

Because BTU vaporization capacity will decline as the remaining LP is reduced, the flame failure issues experienced with the 250 gallon tank, likely occured while there was little LP remaining in the tank.

https://flameengineering.com/pages/propane-information

 

[PatrickTheDrummer]

Water heater model is IGE-199C-5X. I swapped the flame sensor from an identical working unit with no change in behavior.

Bannerman you may very well be right about the smaller tank issue. It certainly seems to be temperature related, and if you are right its only going to get way worse with colder weather and the gas getting used up. I will say that I have the exact same heater on another building with a 250 gallon tank, and even at 2% full it functions perfectly. Is there any possible workaround to make this heater work with the smaller tank?

 

[PatrickTheDrummer]

Also, is there a way to dial back what this water heater calls for? It’s only running one shower. I bought two of them years ago because I got a killer deal, even though they are over sized for my application. If I could dial it back to a 75k heater maybe it would work better?

 

[Terry]

Have you checked the incoming air filter yet?

 

[Bannerman]

Also, is there a way to dial back what this water heater calls for? It’s only running one shower.

When hot water is initially drawn, the initial BTU output will be maximized until the hot water exiting the WH achieves the set temperature, then the gas input will modulate down appropriately to maintain that temperature. While fully modulated, the minimum BTU input for your model appears to be 11,000 BTU.

Perhaps the burner nozzle may possibly be swapped for a smaller orifice size so the maximum BTU output will be reduced such as 150,000-160,000 BTU. It would be advisable to discuss this with Bradford White or a qualified BW technician since reducing the maximum fire rate will likely impact combustion air ratios and other operational settings.

Is there any possible workaround to make this heater work with the smaller tank?

A 100 lb tank will contain approx 40 gallons LP max. 100 lb. propane tank has a 2,160,509 BTU capacity.

In reviewing the prior linked chart, utilizing 2-100 lb tanks @ 40℉ should be capable to supply 210,000 BTU (105,000 X 2) only while there is 40 lbs LP remaining in each tank. If the temperature should drop further to 20℉, then ~50 lbs will need to remain in each as shown in the chart below.
This chart also shows 3 tanks are capable of vaporizing 215,000 BTU @20℉ with only ~15 lbs in each
https://images2.imgbox.com/49/01/C3t677CU_o.jpg

Unless the tank has sufficient surface area to vaporize LP to supply the required quantity of vaporized gas, the tank would need to be either heated or a vaporizer will be required.

Perhaps a more suitable alternative will be to utilize a 123 gallon/420 lb cylinder?

 

[Fitter30]

Hook up a gauge or manometer check gas pressure while running. What regulator are you using? Pipe size and length of pipe?

 

[PatrickTheDrummer]

Terry - the incoming air seems to be just sucked through a grate on the front. There does not seem to be what i would picture as a filter, but a grate with a plate behind it that would capture any decent size debris other than small dust particles. It is clean and unobstructed.

Pipe is 3/4" and the entire run is around 25'. Regulator is Fisher R232-HBF.

 

[Fitter30]

Regulator is rated at 325k and piping are more than enough.

 

[Fitter30]

User manual look at paves 22 & 38 overheat switch powers flame rod control. Couldn't find a service manual but their failure codes in the user manual have alot to be desired. When has the water side been cleaned?

 

[PatrickTheDrummer]

It’s been a couple years since I flushed it. I’m going to do that today. I’m pretty convinced this is the vaporization rate issue. Every night when the temperature drops the heater stops working.

 

[Bannerman]

Although both installations each utilized identical tankless units and 250 gallon tanks, you said one had no issues even with only 2% fuel remaining while the other experienced periodic flame failures. Perhaps the more reliable system's propane tank is located where it receives more sun or radiation from a nearby sun exposed wall, or is more sheltered from wind to allow it to remain slightly warmer.

Frosting on the outside of the tank from the liquid level down is usually a good indicator the consumption rate is only meeting or is exceeding tank capacity. Because your tankless WH likely requires 199,999 BTUs for a short duration only during startup, frost will not have time to develop since the high demand requirement is so brief.

 

[PatrickTheDrummer]

Dude are you psychic? The tank that always works is on the west side of the house and gets direct sun almost all day. The shifty tank is under trees and shade constantly.

 

[Bannerman]

Not psychic, but there had to be a reason one system performed differently from the other. Heat from the sun warming the ground around the tank (and perhaps a concrete pad below) all day will be released at night so the environment surrounding that tank will be slightly warmer 24 hrs/day.

As the tank that experienced the leak was located in a shady area, it will have remained wet longer after each rain, which likely contributed to premature failure of the tank due to corrosion.

 

[PatrickTheDrummer]

Update - my propane guy came out and looked at it. He said the tank could have possibly been overfilled, and I guess he was right. He bled the tank down just a little bit and problem solved.