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Normal startup delay on Rennai V65e

rohanm Member Posts: 2
My plumber and I installed a new Rennai V65e in my studio yesterday. Once it was installed and running for a few minutes it was producing water that felt like the target 120°F. I installed the thermostat and turned it down to 108°. Even though the heater is on the other side of the wall from the shower and only 8 feet from the kitchen sink, it takes 35 seconds before the water comes up to temperature. I turned it back up to 120° and the delay was the same. Is this a normal amount of delay? Is there any way to have it come on faster? I use very little water when shaving and washing dishes and it feels like I am wasting a lot of water just to get the water hot enough to use. This morning I was completely shaved and just rinsing my face when the water finally got up to temp.

Also, I am trying to figure out what the heck the "Priority" button actually does. Is this supposed to be use to select among multiple thermostats? Should I ever bother turning the thermostat Off?



  • Leon82
    Leon82 Member Posts: 684
    The priority would be the shower temp, because you don't want to scald them if you are doing dishes at the same time. But code requires a thermostatic mixing valve usually.

    The delay is from the hot water having to push out the cool water sitting in any lines. This can be a gallon or so depending on the length of pipe. There is also a delay while the unit senses enough flow to turn on.

    The remedy is to install a recirculation system. You can do a loop or one that forces the water back into the cold side.
  • rohanm
    rohanm Member Posts: 2
    Hi Leon,
    With a tanked water heater in the same location as the tankless the delay was less than 15 seconds, and with tank if I turned the hot water off while washing dishes or shaving and turned it back on again it would be hot right away. Right now, when I turn the water off and back on, the water often is hot for about 3 seconds, then tap cold for 15 seconds, then 2 more seconds it is hot again. I'm guessing the 3 seconds is the water already in the pipe and the 2 seconds is getting a flame hot enough to fully heat the water and 3 of the 15 seconds is the hot water moving in the pipe. If my guess is correct that would mean that the heater is not coming on for 12 seconds after the water starts flowing. I'm hoping there is a way to reduce that delay. If the igniter can come on after any water in moves in the hot water pipe, I am OK with that.

    The point of installing the tankless heater was to save energy, so installing a recirculation system would not be a great fit for me.
  • NY_Rob
    NY_Rob Member Posts: 1,370
    If it's a gas (LP or Nat gas) fired device it may have to go through a startup cycle that includes a pre-purge... that can take up to 30 seconds. Maybe the manufacturer has set it for less than 30 seconds... but if it does preform a pre-purge.. it will add some amount of time to the lite off.
  • Leon82
    Leon82 Member Posts: 684
    When you start and stop the water the tankless has to start back up so you always have a "sandwich" of cold water that flows thru before the burner is at full fire and outputting hot water.

    You can use a small buffer tank to fix the sandwich problem. I use a 4 gallon mini tank.
  • rick in Alaska
    rick in Alaska Member Posts: 1,269
    You should have someone turn on the water while you are at the heater and time how long it takes for the water heater to light off after the water starts flowing. It might be that the heater has a problem with the flow sensor and is taking too long to start up. Most of the Rinnai's I have dealt with take about 8 seconds max to start heating.
  • Slimpickins
    Slimpickins Member Posts: 323
    Recirc is cost effective if its done right. Since you probably don't have a return line back to the Rinnai, I would check into the Tacogenie or the AquaMotion Hot systems. Both of those will activate the recirc pump with a motion detector.
    j a_2
  • Jack
    Jack Member Posts: 1,045
    Rick is correct in that you should hold the output line at the water heater and see how long it takes to actually heat. That V65 has a .4 gpm activation rate and will hold operation down to .25gpm. It sounds to me like you have a piping layout issue. I think you will find that the Rinnai is making HW right away, but due to the lay-out of your homes piping it is taking a while to get there. Rinnai recently introduced a wireless function for all water heaters that is backwards compatible to 2006...on everything but the Value Series. Unfortunate as the wireless control makes recirc much easier. Your value series has the same engine, but without the added control features of the HE and SHE units. The Priority button is for homes that have multiple controls. For instance I had 4 controls in my last home. If I wanted to fill the tub, I'd take priority with the M Bath control and set the temp at 104. Once I did so and began flow to the unit no one else could change the temp while the tub was filling. Once the flow was stopped at the tub however another person could take control at another location by hitting the priority on their control, setting a new temp and beginning flow. Very few units used the multiple controls as they required that control wire be run to each location. Today, again on all but the Value series, that operation can be controlled by the wireless module and your cell phone. Get into your owners manual and learn the features of the control. With simple button pushes you can see the flow rate to a tenth of a gallon and check the output temp of the unit. A great deal of tech info is available as well.