Since a Rinnai heater is all self contained, there is a special procedure needed to clean it out. That doesn't mean it cannot be done, but unless you have the proper tools, hoses and support pieces of equipment, this one is better left to the professionals. Only attempt this if you are a serious do-it-yourself type of person with related experience, or you could end up damaging your heater.
Instructions
1. Turn off all water valves to the unit.
2. Hook up the hoses. Using your pipe wrench, disconnect the inlet water hose turning the fitting counterclockwise. Attach one of your water hoses to the inlet with your pipe wrench. Attach the other end of that hose to the outlet port of your pump. Disconnect the outlet hose on your water heater. Connect another water hose to the outlet port. Allow that hose to dangle the end inside of a five gallon bucket. Your final hose will get attached to the inlet side of your pump, and the end of that hose will be placed inside of your bucket.
3. Fill the bucket with the hose end dangling inside with two gallons of vinegar. Do not dilute the solution.
4. Turn on your pump. It will suck water from the bucket and circulate it inside of the Rinnai heater, and then drain back into the bucket, where it will again be recirculated. Allow this circulation to go on for about 30 minutes.
5. Turn off the pump.
6. Remove the bucket of used vinegar and replace it with five gallons of clean water. This clean water should be in a new bucket. The old vinegar can be dumped down the drain. It's a natural acid and won't hurt the pipes or the environment.
7. Turn on the pump for another 30 minutes. This will let the clean water rinse out the inside of the heater.
8. Turn off the pump.
9. Reassemble the system. Reattach all the original hoses and turn back on the valves. Run the hot water through the heater as a final rinse for about 15 minutes, and your system will be clean and working as good as new.
Tips Warnings
While this may not sound particularly complicated, if you do any of these steps incorrectly you could irreparably damage your Rinnai water heater. Be careful, and do not force anything. If you suspect a problem, contact a professional immediately.
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