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Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 22017
Experience:  Licensed Master plumber with 40+ yrs. experience.
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I have a RV53i tankless water heater that is 3 years old..

Customer Question

Hello Marc
I have a RV53i tankless water heater that is 3 years old.. It has not been serviced since we moved in. The last week it has started going cold in the middle of our showers. I have flushed the heater twice and cleaned inlet filter. I have taken off the cover and blew out the unit and checked the vent and I do not see any blockages. But now we get about 5 minutes of hot water and then stops. Error Code 10.
Submitted: 1 year ago.
Category: Plumbing
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can

continue our conversation.

A 10 error indicates a blockage in either the air intake or exhaust. It could also be a problem with the fan. The first thing to check is to look for any blockages

Customer: replied 1 year ago.
I know 10 error code says blockage.. I have already taken the cover off, taken an air hose to the fan and inside. Disassembled the vent and taken the air hose to that.. No visible blockages..
Expert:  Rick replied 1 year ago.

Is this a condensing model (PVC vent)? Do you have an ohm meter?

Customer: replied 1 year ago.
Model Number Rinnai RV53i
- Horizontal Termination without using the Condensate Collector
- The main vent is metal surrounded by PVC
- Yes I have an ohm meterType of Appliance
• Temperature controlled, continuous flow, gas hot water system
• Certified for installation in manufactured (mobile) homes
• Forced combustion / Direct vent
• Energy Star qualifiedRinnai Model Number - REU-VB2020FFU-USMinimum/Maximum Gas Rate (Input)
15,000 - 150,000 Btu/h (Natural Gas and Propane)Electrical
Appliance: AC 120 Volts - 60 Hz
Controller (optional): DC 12 VoltsElectrical Consumption
Normal: 55 w Standby: 2 w Anti-frost protection: 184 wIgnition System
Direct electronic ignitionHot Water Capacity
0.6 to 5.3 GPMTemperature
120° F or 140° F without a temperature controller;
98° - 140° F with a temperature controller;
98° - 160° F available with the MCC-91 controller for hydronic applicationsTemperature (without a controller)
120° F (factory default)Energy Factor
Natural Gas: 0.82 Propane: 0.82Service Connections
Gas supply: 3/4 inch MNPT
Cold water inlet: 3/4 inch MNPT
Hot water outlet: 3/4 inch MNPTIsolation & Pressure Relief Valves Included
Heavy duty forged brass Webstone Isolator valves EXP E2, certified to NSF/ANSI 61-8 for potable waterWater Flow Control
Water flow sensor, electronic water control device and fixed by-passMinimum/Maximum Water Supply Pressure
20 - 150 PSI (recommended 30-80 PSI for maximum performance)
Expert:  Rick replied 1 year ago.

Ok, this is not a condensing unit. I asked because the only other listed cause for this error is a burner sensor fault which is only installed on condensing units. So the only other possibilities since your sure there's no air intake or exhaust obstruction is an improperly installed condensate collar or clogged fins on the heat exchanger. Did you blow out the heat exchanger too? You need the install manual to check the condensate collar installation. Beyond that you may need to pull the fan to be sure there's nothing in there.

Expert:  Rick replied 1 year ago.

I did some more digging. The service manual says only the condensing units have a burner sensor/thermistor but the ladder diagram for your unit shows a burner thermistor so I'm posting a link to the service manual which will give you details on where to probe to check the thermistor resistance (Page 21 & 35). Ohm reading values are in the table on page 21