Parts manual and instruction sheet for Hunter pw50-3 gas heater

If you are installing new tankless in place of 40 gallon gas water heater, then you CANNOT use same vent pipe.
You must use larger diameter pipe that is specified by instruction sheet, and the pipe must be approved plastic or stainless steel to avoid corrosion.
The vent pipe must also have a condensate trap to catch acidic water that drips back down the vent pipe.
The reason is that tankless burn more gas than regular tank-type heater... because tankless must raise temperature quickly as water passes in a pipe.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Gene

Water Heater Timers Save Money

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

Sell it on ebay.

A simple chip change will not convert because the orifice for each gas is different, the gas control valve is different, NG and LP gas each burn at different temperatures and pressures... with propane having higher temps and pressures.

Don't buy tankless computers and expect trouble-free installation and water heating bliss afterwards.
Read the manual for maintenance requirements, and look at the parts sheet and ask yourself how such a complex machine will simply balance and monitor water flow, water pressure, incoming and outgoing water temperatures, gas pressures, vent pressures, gas quality, gas pressures, while connected to water, gas, venting and electric systems inside your home which each have innumerable problems on their own.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Install tank type heater for around $400 and live worry free.
Avoid Rheem products since they do not post service manuals.
http://waterheatertimer.org/Which-is-best-gas-water-heater.html

Gene
h

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

1) Call whirlpool
1-877-817-6750
Need model and serial number located on label on side of tank

2) Copy following links for troubleshoot and repair resources, including service manual by type of gas control valve.
http://waterheatertimer.org/How-to-replace-thermocouple.html
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

3) Get parts sheet from manual that arrived with new product.

4) Otherwise, neither Whitlpool or Craftmaster.has up-to-date product manual, parts sheet, or service manual, rendering their sites near useless for many owners.
Whirlpool site has 'troubleshoot and repair' section, but this is NO help for serious DIY repair.

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

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

Bradford White posts service manuals: Both before and after introduction of ICON (Honeywell) gas control valve
http://www.bradfordwhite.com/documentation/residential/gas.asp

Don't forget to clean air intake locate under combustion parts, using instructions in service manual. Or compressed air. Ample air supply will ensure that combustion chamber does not overheat because of slowed venting of hot combustion by-product that will trip the FV system.
And remove heat trap inserts if water pressure has problem or water heater is humming or whistling

Post question on pro water heater forum:
http://www.thetankatwaterheaterrescue.com/forums/forum3/

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

Thank you for the brand. Approx how old is water heater? 2nd and 3rd digit of serial number are year of manufacture.
For general instructions:
http://waterheatertimer.org/How-to-replace-thermocouple.html

Reliance is AO Smith, and air intake is located on bottom of tank.
Inspect and Clean intake.
Do NOT underestimate need to keep air intake clean because the arrestor screen is fine mesh and once clogged will cause heater to fail. Older models might need full replacement and at least parts.
http://waterheatertimer.org/images/Flame-trap-inspection-325.jpg

Product manual?
These gas water heaters are changing quickly today. The Reliance site shows the 909 but not 805
http://www.reliancewaterheaters.com/lit/om.html
The older designs are different, but instructions shown above will help.

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

Time to call qualified service technician. And watch what that person does to learn about your water heater.
I assume you have Honeywell Icon gas valve. Honeywell makes different several model numbers.

Here is 'typical' Honeywell Icon gas valve service manual for Bradford White, that may or may not apply to your water heater. It shows testing for Icon and disassembly instructions, and error codes.
http://waterheatertimer.org/pdf/Bradford-white-service-manual-44943-D.pdf

Gas water heaters today require yearly service that includes cleaning burner parts and combustion chamber, checking vent and air intake, electrical connections, testing gas valve, checking gas pressure, bleeding air out of gas line, etc. These are things you can learn to do by reading service manual, and making sure you have a spare water heater around to connect real quick if experiment goes wrong.
If Icon gas valve is problem, that control is modular and can be replaced without draining tank.
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot

Before calling service technician, open following links for Rheem troubleshooting resources including error codes.
Error codes are considered start-point for troubleshooting.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/ErrorcodeTroubleshooting.pdf

Error 11 is no ignition.
This problem can probably be solved by routine yearly maintenance shown in instruction manual which recommends: Yearly cleaning, adjustment and inspection of burner and combustion parts.
The yearly maintenance would check incoming gas supply, venting, wiring and grounding, and burner and ignition parts.
All gas water heaters today require same maintenance: tankless require yearly, and tank-type require periodic (1-3 years)

If you have a blower and electronic gas control on your AO Smith water heater, then reading the manual for your specific product is essential for troubleshooting the problem.

As you know, tank-type gas water heaters require periodic inspection and cleaning of burner parts and combustion chamber.. The manual is important for giving instructions and advisories to the homeowner and technical specialist.

If you have ordinary direct vent water heater with mechanical gas control the following link has some troubleshooting resources that might help:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#clean

Upvote the help.
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

I believe my gas furnace has a light on at all times on the control board. You may find an instruction/troubleshooting sheet on or in the sheet metal covers explaining the light and other blinking lights (if trouble occurs).

there are no instructions for doing this.

how do you know it needs replacing? its rare that they need to be replaced.

I can help you, but need to know what is going on with the unit first