Noritz fan seems to run alot

Discussion in 'Tankless Water Heater Forum' started by lifespeed, Apr 23, 2012.

  1. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    I have been noticing the fan (I assume it is the combustion air fan, don't know if there is another fan in this thing) runs alot. After a burn cycle is done the red light goes out, and the fan runs for awhile and then turns off. But a few minute later the fan will fire up again, even though there is no call for hot water. Then it will do it again a few minutes later.

    Is this normal? Seems like an awful lot of fan useage to me.

    I do have a hot water recirc with dedicated line and check valve on the cold water inlet side of the return. However, this is a Redytemp that is on a timer (total of about 2 hours a day), and a manual switch. The pump is not running when I observe this behavior. However, the cold water inlet line can be warm if the recirc has been used recently. Not sure the recirc is causing the fan to run given the pump isn't on, but thought I should mention it just in case.

    Maybe that check valve is interacting with expanding/contracting water on the cold side just enough to trigger the water flow sensor and false start the tankless?

    Edit: this is the NRC-1111DVNG
    Last edited: Apr 24, 2012
  2. tarjan

    tarjan New Member

    Messages:
    9
    Location:
    VA
    As part of one of my quotes I was told this exact situation occurs without an expansion tank, even if I have a thermal bypass as part of the prv. I didn't really believe him... but maybe? Terry here states that the tank is required.

    Do you have one?
  3. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    No, I don't have a thermal expansion tank. So my guess about expanding/contracting column of water may not be that far off? The water flow sensor is being triggered? I assume you are referring to a tank in the hot side output? I suppose this item will not improve the speed of hot water developed at the tap!

    I don't recall in the installation instructions a thermal expansion tank is mentioned. :confused:

    edit: maybe the hot water speed will not be affected if the tank is in parallel with the output, it will just allow expansion/contraction but not require the hot water "flow through".
    Last edited: Apr 24, 2012
  4. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    what does this mean? What is PRV?
  5. tarjan

    tarjan New Member

    Messages:
    9
    Location:
    VA
    Pressure reducing valve, regulator in other words. City water is at 100+psi, which you don't want/need in your house so you use this device to drop the pressure down. Normally located immediately after the main shutoff for your house.

    Thermal bypass is a mechanism in the prv to help deal with water expansion. The PRV brings the pressure to a constant 60psi in my case, when the hot water heater was in operation, cold water would enter the tank at 60psi where it would heat and increase the pressure of the system. The PRV is a one way only device, so water can only flow in and once there it is trapped (closed system). With a thermal bypass, if the water were to keep increasing to something above the city pressure the thermal bypass would allow water back through to drop the total system pressure down which reduces wear and tear on your plumbing system.

    In my county it is code to have at least a thermal bypass or an expansion tank. Both are allowed as well, but I do not have an expansion tank yet.
  6. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    Is the thermal bypass the valve that blows over-pressurized water (typically onto the garage floor) out of the hot side of the water heater if there is some unforeseen problem? I've never seen an installation that does not have this. They are required by code, of course. But this valve is supposed to never operate except in emergency circumstances. I have a pressure regulator at the inlet to the house, far from the HWH.

    I checked with Noritz, and they claim I should have a check valve in the recirc pump output to the HWH cold inlet, as well as a check valve in the HWH cold inlet (which I already have). And an expansion tank between these two valves and the HWH inlet. I guess water is moving, expanding, or thermosiphoning and causing the HWH to false start.

    Noritz_recirc.jpg
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,149
    Location:
    New England
    Code may or may not be up on tankless systems, but generally an expansion tank is required when you have a PRV. Since a tankless only runs when there's a demand, you don't have a large tank of water that could be being heated and expanding.

    If you do install an expansion tank, they are not designed for installation on the hot side. If you do put one there, it won't last as long as where it is designed to be (on the cold side).
  8. tarjan

    tarjan New Member

    Messages:
    9
    Location:
    VA
    There is an overpressure relief valve on your TWH. The same design as the one on a water heater I believe. The thing with the lever.)

    That is not what I mean by thermal bypass. That is actually part of the PRV. If you look at the diagram, look at the cold water supply, the first thing inline is a PRV which you will note is shown as a one way switch. Built into the prv is a system that regulates the pressure of the inside water to always remain at 60psi, any time it drops below that, water is allowed to rush in from the city source, but only if it is higher pressure than your internal water.

    Here is the important point: At any time the pressure inside your house is equal to or greater than the psi outside, the prv stops the flow of water and will not allow any water to go back out.

    This is where the thermal bypass comes in. Assuming the prv is set to 60psi.

    * You have 50psi in your pipes, which is below the setting on your PRV. City is having issues and pressure dropped to 40psi. No water will flow into or out of your home because the source is less than your house.

    * Tank heats up, pressure builds. You now have 80psi in your pipes, which you don't want. The city water is also 80psi. Nothing will happen because the pressure is equal but water can flow in if a tap is opened AND the pressure in your pipes drops to below 60psi.

    * Tank heats up, pressure builds. You now have 135psi in your pipes, which you really don't want. The city water supply is at 100psi. The thermal bypass will allow water to be pushed back out of your house into the city water supply, getting around the prv's one way nature. It is code to hopefully keeping your pipes from bursting. Basically it is a low flow high pressure regulator going the reverse direction, but only in dire situations.

    I used 135psi as that seems to be a reference point for how high it actually has to get before the thermal bypass will allow flow.

    Expansion tank on the other hand should keep your system constantly at 60psi (or whatever is right in your situation) no matter what.
  9. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    I see. The 'one way switch' is a check valve, which is a one way switch for water. I should have included the legend from the Noritz diagram.

    So yes, I will need an expansion tank as discussed. I am also experiencing some odd temperature fluctuations (water cools noticeably) in the shower. I do not think I can attribute this to either the Toto thermostatic shower valves or the temperature regulation of the Noritz TWH. I think that recirculation loop is moving cold water into the hot water line by virtue of lack of a check valve at the recirc pump outlet in my system, as shown in the diagram.

    I'll get it fixed shortly.
  10. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    I see the Redytemp 4000D circulator is supposed to have a check valve built into the output, so I should not need to install one. In fact, my system should be configured correctly except for the lack of an expansion tank. Which, to be honest, I do not see as likely to be responsible for my issues described above.

    I suspect there may be a problem with the check valve at the circulator output. I will diagnose this by closing the valves at the input and output of the circulator pump and see if the symptoms go away.
  11. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    I closed the recirc pump valves and unbolted the pump. The HWH no longer runs when hot water is not being called for. Blowing on the check valve does not reveal any problems, but I don't think that is as conclusive a test as removing the recirc pump and closing the circuit.

    The built-in check valve is a cheesy plastic job. I wonder if that is the problem? There are brass check valves available, I wonder if I should use one of those instead of the built-in cheap valve?

    The shower valve temperature issue remains, and is clearly a failure of the Toto TSTAR valve thermostatic cartridge. See here.
  12. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    OK, this is one of those classic operator error moments. The Redytemp unit is cleverly designed to accept any 120V timer to operate the unit on a a schedule, as well as pushbutton from a momentary switch next to the disposer at the kitchen sink.

    The problem turned out to be nothing more than the timer set to "on" rather than "auto". Doh!
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