Intermittent cold H2O after 3 years of no-problem Rinnai Tankless WH? Why?

KarenB

My Rinnai tankless WH worked for three years with no problem. Then, last summer, showers began to be interrupted (not always) by periods of cold water that could be relieved by turning shower off, shivering a minute, then turning back on. Then, these events became more frequent, then came quicker and quicker. Had a technician come last week, who cleaned the unit. He said there was some scorching on the heat elements, and that while he had fixed things, it would be a good idea to install a dedicated pipe from the propane tank to the unit. Hot water still stops about 2 minutes after starting a shower, and restarts after about 30 seconds of shivering. My question is this -- why would the piping become insufficient suddenly after three years? The problem has persisted through hot weather with no heat on, to cool with heat on. It is in all lines (dishwashing, showering). I want hot water, but am not sure that this piping business, which is quoted to cost near $500, is the reason. The Rinnai used to supply endless hot water to multiple showers, washing machine, dishwasher, summer or winter. Please help me to decide if the new piping is the way to go or there is some other issue. Thanks.

Ironman

The gas line may be under-sized, but there's no way for us to tell without specific info about the total btu rating of everything connected to it, line sizes, length of run, etc.

Still, I don't think that's what's causing your problem. Three basic things to look for:
1. Was the heat exchanger properly cleaned by pumping cleaning solution through it long enough?
2. Is there a water inlet strainer on the unit and is it clean?
3. The flow sensor may be dirty or defective.

If all these things check out OK (doubtful), and the contractor still thinks the gas line is the issue, then make him guarantee in writing that what he's proposing will fix your problem or else you won't have to pay for it.

Snowmelt

Gas piping, just from experience, sometimes the meter to the street has failed, first thing you need done is to check the gas pressure.

KarenB

Yesterday I spent time on phone with Rinnai technical assistance, and we found code 25 (condensate). We discussed the drain arrangement the plumber had put in for condensate, which the technician thought was problematic and deserved attention. I called the tech who had cleaned the unit on Friday, and he came back and flushed the tubing from the unit to the drain (a run of about 15 feet to gravity), and the Rinnai seems to be working fine now. However, he found that the opening gas pressure was 8.11 (sufficient), but once the unit fired, pressure went down to 6.85, which he said was insufficient. I am deciding whether to run a new gas line/pressure regulator from the propane tank; I thought it illogical that the gas pressure would be a problem since the pressure is the same as it was for past 3 years -- but I did not consider the issue of meter failure, which certainly could be the case (per Snowmelt). (A clue here is that the propane company replaced the tank last month because there had been a slow leak -- was the meter replaced? -- I don't think so). And the possibility of a dirty flow sensor meter or other issues as Ironman has brought up, must also be considered. I will attempt a nice long shower later today, and see what happens....if it ends in cold water again, we will be on to the very helpful suggestions -- thanks. I'll let you know the outcome of the shower.

Ironman

If it's propane, chances are you don't have a meter since the LP co. bills by how many gallons they put in the tank.

You should have an incoming pressure of 11.5 - 12.5" WC with nothing running. With everything running, including the Rannai in high fire, the pressure should NOT drop below 10.5" WC. If it does, the piping and/or regulator is undersized.

This shouldn't cause the problem that you're describing, but it will cause the unit to under-fire resulting in less output during high demand.

Jack

Bob is on the money here. I will say, as long as you are up to your elbows in this, do figure out how to access the fault history on the display, take a sharpie and mark the date and the codes that you are seeing.

RobG

If the unit worked in the past, your LP provider should come out and inspect and probably change the regulator. As Bob said above, those pressures are too low.

KarenB

Thanks, guys. I will get with the propane company -- the shower is working now but for the long run, we need to increase that pressure, and the fact that the tank was not delivering full pressure for months before it was changed out suggests that we need some changes -- and would explain the development of this problem last summer. This has been really helpful!

icesailor

The LPG dealers I always dealt with would have been on this like flies on something dead. The service guys I worked with would have had those regulators changed and going up to spec's or they'd be suggesting a direct line from the regulator to the appliance.

What's the size and developed (overall) length of the gas line to the heater? Are there any other fixtures coming off the line?

KarenB

length of gas line from tank to heater is about 10 feet. The single line supports the furnace and the cooktop as well as WH.

neilc

had a same type problem with my domestic tankless,
wound up having little bits of leaves in the 1st of the 2 burner pairs for low fire,
it would make and burn 4 or 6 tubes to start, then when it down fired, the clogged 1st tubes would break their flame sensor,
took the whole burner apart and found 3 tubes, 2 of them bad, with leaves, and more in the fan, waiting,
added some 1/4" hardware cloth to the inlet of the concentric, that was 5 plus years ago now,
damn that water got cold, shut it off and restart, lots of sad showers then,
no problems since.

Ironman

KarenB said:

length of gas line from tank to heater is about 10 feet. The single line supports the furnace and the cooktop as well as WH.

Need to know the btu rating of the furnace.

KarenB

Im out of town today, but when I get home tomorrow, I will check that and report!