Rinnai tankless water heater problem

kj64

I am a homeowner with a Rinnai R53i-1 installed in 2007. It is not heating when the hot water taps are turned on, but it shows no codes. My operation/installation manual suggests checking the inlet supply filter, the water flow turbine and the resistance of the water flow control sensor. The filter is clean and the turbine spins freely. I am not sure how to check the resistance of the flow sensor (I have a multi-meter but am not sure where/ how to test the unit). Rinnai customer service looked at a parts diagram and pointed me toward this flow control kit which does appear to be the one for my heater http://">https://supplyhouse.com/Rinnai-104000017-K-Water-Flow-Control-Assembly-Kit. I have already had the unit out and replaced it (the same assembly, not a new one). The heater fired off a couple of times but is dead again.

The heater is flushed yearly with vinegar. There is sufficient flow to trigger the unit in normal circumstances. The heater generally functions correctly, although there have been intermittent occasions when the unit stopped in mid-shower. Usually it could be coaxed back on by opening another faucet. I suspect something is faulty in the flow sensor. Is there something else I should be looking at? I am leaning toward ordering and replacing the flow control assembly kit as opposed to calling in a tech, as my regular plumber is not that experienced with Rinnais and I'm not sure who is reliable around here (near Burlington, VT).

I have heard that the only dumb question is the one you don't ask so here goes. How the heck does the control work? How does the sensor pick up the turbine rpm's? The electronic package is splined to the valve but to what purpose?

Fortunately the sun has been shining enough to keep the solar tank upstream of the Rinnai warm, but October is coming up...

kj64

I installed the new flow control assembly which appears to have cured the problem.