State select pr650povet hot water heater controller, roberts haw continulisly flashing water htr wont turn on till reset or ignitor cleaned but then only works for short time

It sounds like you have a scale problem which can seriously affect your water flow. If the water heater is older than 10 yrs, then this may be your problem.
If so, try draining the htr. First off, turn your heater off. If electric, turn off 30 amp two-pole breaker in your elec panel. Your elements may also be scaled up, thereby reducing their effectiveness. If you have little hot water, your bottom element and t-stat may be bad. If the electric heater is older than 10 yrs old, then you may want to consider replacing it as the average lifespan of a heater is about ten years. If gas, just turn the control knob all the way down. Attach a garden hose to your heater drain valve. Run the hose outside and open the drain valve with the water supply to the htr still on. This uses water pressure to blow out the scale that is likely clogging the drain valve. Blow it out for ten seconds, and then shut the valve feeding water to the htr.
Shutting the valve creates a vacuum so the draining will slow way down. To speed this up, turn on hot water all around the house. Do not do this with single handle faucets because cold water will cross over. Only the hot on two handle faucets should be opened.
If you don't have any two handle faucets, you can either turn off the water main and open the single handle faucets, or flip the lever up on the relief valve located on top or on the side near the top. Pull it so that it sticks straight out. This locks it in the open position and allows air to enter, and water to exit. Drain until no more water comes out.
Please keep in mind that if your heater is old, the scale may be the only thing keeping it from leaking, and this may expose that leak.
If none of this works, your inlet and/or outlet on the heater may be scaled up. This requires the removal of piping and scraping out the scale. Once again, if the htr is old, (over 10) you may want to consider just replacing it.
GOOD LUCK!

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

Clean air intake located on bottom of heater?
Gene

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

Possibly the air intake located at bottom of heater needs to be cleaned with feather duster under water heater.
Read your product manual for steps.
Copy following link for general illustration.
http://waterheatertimer.org/images/State-select-air-intake-400.jpg
http://waterheatertimer.org/pdf/Flame-Arrestor-Screen-Cleaning.pdf
Other causes can be bad intellivent gas control valve, poor venting, hot attic, low gas pressure, dirty combustion parts, tripped FV system.
Copy following link for available intellivent troubleshoot resources:
The service manuals are large files and open slowly.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

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

thermostat?
what are you trying to do, replace, reset?
most hardware stores have these, but I would replace both unpper and lower, not just the one.

make sure you set both to the same temp, the heater will work better.

just follow the instructions in the package. make sure you turn off the power before you start.

sounds like one of the saftey relays might be going bad. or the ingniter might be cracked or need cleaning

lucky for you I jst did one of these the other day same problem,, check the wires on the ignitor, some of them are thinly coated and causes them to short out, wrap electrci tape around them individuly turn off the unit , wait 30 sec, turn it back on at it;s lowest tem hold both temp buttons at the same time till lights come on the after it lights set the temp

Th epproblem you are most likely have is from a safety called a flag switch usually located either in the blower or right past it. When you unplug and replug you reset the switch. Sequence of events.  1 fan comes on. 2 switch is made from the airflow of the fan.  3 ignitor come on 4. main gas valve opens and ignitor starts flame. 
You are being stopped at step 2 when the fan does not move with the air. This shuts off and out the water heater from calling again.  Find the fan switch and make sure it moves easily. They get dirty and also dry from lack of lube. Good luck.  

did you turn the unit off before hooking it up ? Any function on a tankless rennai the pwer has to be turned off and the priority button has to be pushed in,, if you have the manuel it tells you haw to do this,,

in order to reset the unit you will have to turn the temp all the way down then unplug the unit for 5 min,, remember it is a computer and it knows, after plugging in back in after the five min, reset the temp open up a fauset while doing this, that way it will be regestering the flow of water to set the temp by

I have fixed mine. The problem part is the Ignition Control module. It is made by Robert Shaw part # SP10758. I paid $93 plus shipping.

Works great now. A repairman wanted to sell me a gas valve for $488.
Watch out for these people.....