I have a Bradford White model# MITW50L6CX10, serial# TA4176718-130-131, 48 gal., gas, power vent. The vent is running constantly, and when the burner lights it burns erratically even going all the way out only to re-light and continue with erratic flame.

Check size of breaker check cable load .

Feb 2013
1) Rheem/EcoSense tankless product manual does not have specifications for length. Error 11 will let you know if venting is improper.
Often, tankless are installed outside because unobstructed venting is key for combustion of the amount of gas coming out of 3/4" gas line.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

2) Copy following link for Bradford White venting: Exactly same as Rheem, but more installation detail. No maximum lengths given.
For lengths greater than 5 feet, a condensate trap must be installed. Acidic water from hydrocarbon combustion will damage metal, and destroy heat exchanger inside tankless if water drips back into unit.
http://hometips.me/Tls/Venting-Bradford-White-tankless-gas.pdf

3) Copy following link for tank-type power vent tables:
Generally, the longer distance requires larger vent diameter, and there is max number of elbows and/or air-flow restrictions.
http://hometips.me/Mar/Bradford-White-Power-Vent%20-tables.pdf

4) Otherwise call Rheem/EcoSense, and add comment saying what resources they offer.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) Do you mean NG natural gas to propane?

2) Most companies do not support gas-type conversion, especially with modern FVIR-compliant heaters. New burner, gas control are required at minimum.

3) Contact Bradford White and include model number, serial number that appear on label on side of unit.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) I believe you can immediately elbow the PVC pipe.
There is a limit for how many elbows can be used between blower and termination, and limit is determined by diameter of PVC pipe.

2) Copy following link for venting resources and typical Rheem and Richmond power vent manuals, and diameter-elbow pdf from Bradford White.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#venting

3) Richmond is Rheem. Product manual will show specifications for venting.
Product warranty is voided if installation does not follow specifications shown in manual.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Probably cheaper to fix existing water heater.
The problem might be the power vent, or the power vent might be short cycling because the gas control valve is bad, or vacuum switch has gone bad.
Call Bradford White and get their recommendation for your specific model.
http://www.bradfordwhite.com/contact.asp
http://www.bradfordwhite.com/supportserv.asp
http://www.bradfordwhite.com/findaserial.asp

Bradford White is very good brand of water heater
Rheem, Richmond, GE are good.
I prefer the AO Smith, American, State, Reliance, Craftmaster. Kenmore, Whirlpool brand since air intake screen is located on bottom of unit and can be inspected and cleaned without removing burner.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Some how you have disconnected the sensor that tells the main burner that the fan is on. Its trying to light but cant. On some models there is a air pressure switch that reads the pressure inside the vent pipe itself. It will have a small hose on it and if that has cracked or was not replaced it wont light. This is how its supposed to work--- vent fan comes on,sensor confirms fan is on,hot surface ignighter starts to glow red,and main burner is opened,another sensor confirms that main burner is lit,then hot surface ignighter turns off. Hope this helps.

Why is it always Rheem problems?
Every water heater problem is Rheem.
And Rheem doesn't post any service manuals, like the other two big manufacturers, AO Smith-American, and Bradford White.

Copy following link for troubleshoot by gas control valve.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Scroll up and find pressure switch heading among links.

You can install gas control valve yourself.
http://waterheatertimer.org/pdf/How-to-replace-water-heater-gas-valve.pdf

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

The slightly warm water makes me think of a thermostat problem. The fact that the heater is 10 years old I wonder how hard your water is. Calcium build up kills water heaters. But the yellow flame you mention could be the results of dirty orfices. May want to have a Pro look at that.

the Thermos coupling has gone bad, call the manufacture and talk to customer support.