Issues with Sanden CO2 Heat Pump Water Heater

crewkip

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?

Icarus

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.

kieran@smallplanetsupply.com


http://www.smallplanetsupply.com/sanden

It certainly sounds like an installation issue.

Icarus

SuperTech

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

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.

crewkip

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

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

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

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.

mikeg2015

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

> @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.
>
> kieran@smallplanetsupply.com
>
>
> 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.

tim smith

Just a check 3 yrs later, how has the Sanden held up for you. If you still have it?
Tim

H2OBandit603

I installed one with the 119 gallon tank and a swing check on the incoming hot water from the heat pump just to be sure it’s not having any cross contamination or thermal siphoning issues as mentioned before.  Other than power outages and such that have caused the heat pump to lock out on an error code, once when it was VERY cold and the heat tape doesn’t seem to run when the unit is locked out since it’s wired to the heat pump circuit board, it’s always come back after a few breaker cycles with 3 minutes in between.  Really happy we got the 119 gallon tank it lasts all day and my father’s 15 gpm tub filler usually clicks it on at the end of the day.  The water is 145 F when the ambient temp is below 65 F and 150 F above 65 ambient.  We also insulated all the hot water lines.  No mixing valve it’s done at the shower and you can definitely burn yourself the water is nice and HOT.

in my opinion this is the best water heating solution.