Rinnai R85 Tankless hot water heater issue

rosscanant

I have two 10 year old Rinnai tankless hot water heaters on propane. The most used one (master bath) has started having an issue. It will either not start up (I believe it lights then shuts down after 15 seconds or so) or it will drop off in mid shower and not come back on unless we turn off all flow and restart. It seems to help if we keep a sink running with the shower leading me to believe it is a flow sensor. I don't believe our shower has changed at all. I'm thinking it could also be a flame sensor but not sure? I have descaled it and blown out the heat exchanger. Fan is working fine.

Jack

What temp is it set for?

rosscanant

140 degrees. Has been set there for 5 years.

lchmb

Have you ever had the unit serviced to include descaling the HX? May be time to get it done..

Jack

Set the temp to 120. The R85 has a min flow of .4 gpm to initiate operation and a min input of 10kbtu. 140 is way to hot for domestic use, other than a DW. By lowering the output temp you increase the percentage of hot to cold. That should minimize the margin issues I think you are seeing.
Also, prior to changing the temp do a flow test. Run the shower at your comfort level and read the flow rate on the controller. Lower the temp and read that flow. Please report the difference and whether the shower cuts off. Also what, if any, error codes are there in memory?

rosscanant

Yes, I spent Saturday descaling both units and cleaning the heat exchanger, fan, and burner area. It did seem to help. The 140 setting is what the wife likes in the shower. She can stand it hotter than I can.

rosscanant

I'll drop it back a bit and see what happens. Thanks.

Jack

Tell your wife that the shower valves are set by code to no more than 110-112*. As well, if you sit in a tub that is more than 105* you are no longer bathing, you are par-boiling. Can you pull the error code history?