What should the min and max manifold pressures be on my tankless water heater PTG2-42PVN. I'm under 3200 feet in elevation.

Which type Richmond water heater?
Is this a tankless water heater or tank-type?

Tankless are notorious for 'cold water sandwich' under exact conditions you describe. You might need tankless with larger BTU burner.
Don't install a tankless.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

If you have tank-type water heater, then I suspect a clog in the hot water line, or single-handle faucet cartridge in show is going bad.
Same problems can contribute to tankless problems.
http://waterheatertimer.org/Low-hot-water-pressure.html

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Open following links for Rheem troubleshooting resources, including Rheem chat, error codes, and possible manual.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf

Error codes are considered start-point for troubleshoot.
Error code 24 is malfunction of operational switch: press max or min button on PC board to reset, -or- replace PC board.
Max-min button is sometimes located above dip switches, and can be 1 button that is rotated with screwdriver or 2 separate buttons. Look at wiring diagram in manual that came with product.

Fix most tankless problems yourself, same day, for $330.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

Things to Check:

1. incoming gas pressure (minimum 5" when unit firing)
2. Make sure damper on top of unit isn't sticking
3. check vent length and #elbows versus installation manual specs
4. if above 2000', disconnect high elevation termination

If these all check out, you'll probably need to do a manifold adjustment. Call Noritz for assitance on this.

Filters always reduce pressure.
You can add a pressure tank between filter and tankless.
Tankless are sometimes like bowling on a ship.

Add a comment saying how you fixed problem.

Fix most tankless problems yourself, same day, all brands for $330.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

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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.

Possible flow sensor issue. Check to see if your water pressure fluctuates a lot or is fairly steady. These units are sensitive to the pressure. take care.

open cover.. find buttons min/max press nim then press mas and then hold min and max presses for 5 seconds or so. Power off controller and power back on..You have reset your fault code til next time.

norm point 7 of 1Bar hogh/pressure release blows norm just under b3Bar best of luck

Hello. let me help you. The water pressure is what it is in the house. In other words, the tankless water heater doesn't increase the pressure of the water, it only heats the water. There is no official minimum pressure but the minimum pressure you would be happy with in any home would be 20 pounds per square inch, PSI.

See this link:

http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/water-heaters/tankless-water-heaters/overview/tankless-water-heaters-ov.htm

Then think about it

no the tub faucet is the only faucet that is wide open you might have to not run full blast on the faucet , your tankless water heater is under sized for the application, to many gallons per min going thru the unit, look at the rating chart for your unit, the r94 is only 9.4 gallons per min, and a tub faucet can be upto 5 gallons per min, depending on the faucet,,