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Issues with Sanden CO2 Heat Pump Water Heater

I had a Sanden CO2 Heat Pump Water Heater system with a 43 gal tank installed just under 6 months ago to replace an aging 80 gal electric tank.

While I am impressed with the energy savings, there are two issues that have plagued the system since install. I can't say Sanden technical support has been helpful or very responsive to my concerns which has been disappointing.

The system is used for DHW only. I have a Taco recirculation pump. The system was installed by a professional in the area, and far as I can tell it was done correctly.

The issues are as follows:

1) Wide fluctuations in hot water temperature. If you request hot water at the wrong time (basically right before the system thinks it should start making more hot water again) you may end up with a barely warm enough shower. I like decently warm showers, as does my wife, so maybe this isn't an issue for most people. But this was never an issue with our old electric tank. I know the system is set to turn on at 113F, but I have found at times that some showers are only getting water in the 105-106F range for the duration of the entire shower. If the heat pump was recently on then the water is piping hot and there are no concerns about temperature. This is an issue no mater the temperature set point (150F,160F,165F etc).

2) System pressurizes all of the water lines in the house. Anytime the heat pump is running, it pressurizes the lines in the house. If you open a faucet or flush a toilet you notice a distinct increase in pressure that subsides after about 5 seconds. This hasn't caused a problem....yet. I can hear my toilets release a bit of water here and there when the system is on. This is more annoying than anything else. The setup does not include an expansion tank like my old resistance hot water heater. This was not an issue on the old resistance hot water heater setup. Seems very unrefined, especially at this price point.

To trouble shoot these issues I turned off the Taco recirc pump for several days. The issues continued.

Any thoughts?

Comments

  • Icarus
    Icarus Member Posts: 143
    First...I am not a Sanden expert by any stretch. I am only learning about them by designing a combi system yet to be installed. One thing I know is that counter intuitively you want to keep the water tank stratified such that there is always cold water at the bottom. The Sanden is much more efficient with a higher Delta.

    Second, I would get in touch with Kieran at Small Planet Supply, a wholesaler for Sanden, and he has been very helpful in helping me design the combi system I am working on.

    [email protected]


    http://www.smallplanetsupply.com/sanden

    It certainly sounds like an installation issue.

    Icarus
  • SuperTech
    SuperTech Member Posts: 1,691
    I can't think of any logical reason why you wouldn't need a thermal expansion tank, especially if the previous water heater was installed with one. It sounds like some of your issues are due to this. Are you on a public water supply or on a well?
  • Zman
    Zman Member Posts: 6,994
    edited February 2020
    I think your installing contractor should be dealing with all of this. I assume you paid them to install this, they need to make it right. Show them the manual and nicely ask them to fix it.

    You may have an issue with the tank sensor.
    The system may have a schedule programmed that sets back the temp automatically.
    You should have a thermostatic mixing valve installed per manufactures instructions.
    Get an expansion tank installed before you damage something.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • crewkip
    crewkip Member Posts: 3
    They appear to have followed the installation manual, which does NOT show an expansion tank as part of the install.

    I am on public water which comes from a series of wells in the area. The water PSI coming into the house is around 40-50 PSI at most.
  • Jon_blaney
    Jon_blaney Member Posts: 136
    How old is the tempering valve? That my need attention. Also, have you considered adjusting the shower mixing valve? How are the water temps in the sink and tub?
  • crewkip
    crewkip Member Posts: 3
    Th tempering valve is brand new and was installed with the Sanden unit.

    The mixing valves at the shower are not the issue.

    At faucets with separate cold and hot valves the hot water temperature will fluctuate just the same as the showers.
  • Jamie Hall
    Jamie Hall Member Posts: 17,121
    If there is any form of backflow preventer or check valve on the water lines coming to your house or before the water heater, you must have an expansion tank. It may not have been on the install diagram because it is required by code in some areas, and simple good practice everywhere. It's not part of the water heater -- it's part of the plumbing.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ZmanSuperJ
  • mikeg2015
    mikeg2015 Member Posts: 1,183
    Does the circulation pump have check valves in the lines? Depending how it piped, the hot water can end up feeding from the recirc line and mix with the hot water line. This will cool the water at a shower or faucet.
    SuperJ
  • SuperJ
    SuperJ Member Posts: 605
    > @mikeg2015 said:
    > Does the circulation pump have check valves in the lines? Depending how it piped, the hot water can end up feeding from the recirc line and mix with the hot water line. This will cool the water at a shower or faucet.
    >
    >
    Agree. I wouldn’t just stop the pump. Valve off the recirc line for troubleshooting.


    > @Icarus said:
    > First...I am not a Sanden expert by any stretch. I am only learning about them by designing a combi system yet to be installed. One thing I know is that counter intuitively you want to keep the water tank stratified such that there is always cold water at the bottom. The Sanden is much more efficient with a higher Delta.
    >
    > Second, I would get in touch with Kieran at Small Planet Supply, a wholesaler for Sanden, and he has been very helpful in helping me design the combi system I am working on.
    >
    > [email protected]
    >
    >
    > http://www.smallplanetsupply.com/sanden
    >
    > It certainly sounds like an installation issue.
    >
    > Icarus

    The stratification is really important for top performance. A high performance home run plumbing system with the smallest diameter pipe (for low water content) is preferable to recirculation.