At wits end with Rinnai RL75I water pressure problems

[DonJr]

I am wits end with my Rinnai RL75I tankless unit. One person can shower and the rest of the house is a trickle. The unit is 10 years old, has faithfully been descaled every year, including 6 months ago and a few days ago (both times minimal sediment). The current water output is 2.6GPM with a 6.0GPM input. With the unit off the input water pressure is 55psi in at cold water intake, and 45psi at the hot water exit. The
combustion unit has been cleaned and blown out with an air compressor. The fan has been removed and cleaned, with about a dozen insects removed. Fan runs true with no wobbles. Exhaust and intake has been cleaned from unit to outside (two feet) with only one small dirt dobber nest found. Today I replaced the water servo valve with genuine Rinnai parts. Still same 2.5GPM flow. DIP switches are at factory settings with 120 degrees set. As a precaution I have a new fan ordered to be delivered today. Other than that possibility I have exhausted my options.. Any help is greatly appreciated!! Please HELP!

 

[Fitter30]

I am wits end with my Rinnai RL75I tankless unit. One person can shower and the rest of the house is a trickle. The unit is 10 years old, has faithfully been descaled every year, including 6 months ago and a few days ago (both times minimal sediment). The current water output is 2.6GPM with a 6.0GPM input. With the unit off the input water pressure is 55psi in at cold water intake, and 45psi at the hot water exit. The
combustion unit has been cleaned and blown out with an air compressor. The fan has been removed and cleaned, with about a dozen insects removed. Fan runs true with no wobbles. Exhaust and intake has been cleaned from unit to outside (two feet) with only one small dirt dobber nest found. Today I replaced the water servo valve with genuine Rinnai parts. Still same 2.5GPM flow. DIP switches are at factory settings with 120 degrees set. As a precaution I have a new fan ordered to be delivered today. Other than that possibility I have exhausted my options.. Any help is greatly appreciated!! Please HELP!

Page 27 has the water pressure drop. 6 gpm = 12 lb drop. All heaters of this type have a high pressure drop. Just look at the chart just 1 gpm to 7 gpm 12 to 15.
Look at the bottom curve takes the temp rise to gpm. 120° with 50° water 70° rise

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[GReynolds929]

Fan won't make a difference. Was the inlet filter checked and cleaned yet? Inlet water temp?

 

[John Gayewski]

A 6gpm inlet? What do you mean by that?

 

[Fitter30]

Post 1 wrote he has 6 gallons per minute

 

[Reach4]

If you set the temperature to some low temperature, such as 98F, do you get more GPM out?