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225 posts

Master Geek

  #3166461 30-Nov-2023 17:27
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Installed today, happy with it so far, especially the sound level, very quite compared to my central heating heatpump!!






Can't speak too much for the general case - but in the case of the Rheem unit its a soft start, so only requires only about 5 amps, single phase (notwithstanding the 20 amps mentioned on the brochure, which Rheem confirmed).   This is well within the realm of a standard Shelly IOT device [which include timers if thats how you want to do it] which you can just wire onto the circuit - and if you have a switch for it, behind the switch. (and this is how I do it on mine)     As I recall, the Rheem units also have a limited ability to turn themselves off during a peek time - but don't handle daylight savings and did not have the amount of flexibility I was after.   I don't imagine a competent sparky would need to charge much more then the initial callout fee.    The variant of Shelly I am using is the Shelly Plus1PM - which I believe has NZ certification and cost me about $60 for the hardware.


I was reading online that for units with greater draw you can use a Shelly type device to feed a larger relay, or sometimes get away with a "snubber", which I understand to be some kind of Capacitor that helps with the initial startup load. 





David, did you put the shelly device behind the isolator switch? Am looking to do something similar as my docs say the power input is 2.5kw which is within the 16amps of the Shelly Plus 1PM.







Trade NZ and US shares and funds with Sharesies (affiliate link).
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  #3166598 30-Nov-2023 22:02
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I put the Shelly between the switchboard and the unit (In my install there is a mounting box on yje outside of the house where the cable enters the house).

were it true that the unit drew 16 amps the Shelly would need a snubber but Rheem advised that it doesn't draw anything close to that). It also has a soft start which is helpful in reducing stress on the relay.

(Apologies if the formatting of this message is bad - im writingbthis on my mobile and the site appears a bit broken)

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  #3166731 1-Dec-2023 09:42
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Here is the (Redacted) correspondence I had  with Rheem which may be useful  - 



RE: Rheem GAUS-300FQS power draw


From invalidsignature ***> To (me) Date 2022-05-19 15:41   Hi David


The only reason the manual requests a 20A supply is this is an Australian requirement for any permanently wired appliance to be supplied with a dedicated 20A supply. We have just left it in the NZ option as it is good practice to have a dedicated supply to ensure uninterrupted supply.


The Compressor is a scroll soft start compressor so From your specs I would say your Shelly is capable.






From: (me)
Sent: Thursday, 19 May 2022 12:37 PM
To: )redacted)>
Subject: [EXT]Rheem GAUS-300FQS power draw




Hi [redacted]


I've been doing more research on IOT switches so I can turn the power to my unit off at peak, and I've found a device (Shelly 1) which can toggle power for up to handle (at up to 250v) 16 amps resistive load, and 8 amps (COS = 0.4), which I take to be its ability to handle a resistive load.  (ie to handle 2 peak periods per day and make better use of the solar system I'm looking at as well)


In the product data sheet for the Rheem I see the Electric Input (at 19 degrees c) is 0.95kW (so roughly 4 amps),  but there is another line that says "circuit 20 amps").   Do you know why there is such a large discrepancy between these 2 values ?    Relatedly, do you know if the heatpump has a "soft start" ?


Most importantly, can you comment if the Shelley is adequately specced to turn this device on and off?


Kind regards,
David Go




On 2022-05-03 15:36, (redacted) wrote:



Hi David




Thanks for your enquiry and the answers are as follows.




1)Yes this system does have a real time clock RTC and remembers the time for up to 7 days after a power failure or power off.


 *Settings such as block-out times are remembered for the time being beyond seven days, but cannot be stated clearly.


2) Yes only one block out time per day can be set.


3)Yes it is okay to control the power to this unit via a external time clock as long as the unit has power for 5 hours per day and has leginalla mode etc to complyand offers frost protection. I do not recommend this option.




Please find below more detail on how to set the time and block out modes.




10. How to Use Operation Panel


1. How to Operate


1-1 7-Segment Display


7-segment display on the operation panel ordinary displays the current time as a function of the Clock Display Mode. However, the display is switched to the Display Sleep Mode and turns off when no panel operation is performed for more than 60 seconds. Display Sleep Mode is cancelled when either of "UP", "DOWN" or "Enter" key


is pressed. When an error is occurred, a red LED on the operation panel turns on and an error code is displayed on the 7-segment LED display. The panel does not turn to the Display Sleep Mode while the error code is shown.


1-2 Time setting


This product contains a built-in clock.


As part of the water heating cycle logic refers to the current time, it is necessary to set the clock before starting to use the product. The current time can be set in the Clock Setting Mode as described below.




There is no need to adjust the time setting for the daylight saving period. Even if the installation is conducted during the daylight saving period, the clock setting to the ordinary time (not daylight saving time) is preferable.


1. Switching to Clock Setting Mode




With the display reading 000X (X being the time elapsed from starting the unit) Press the "Enter" key to switch to the Clock Setting Mode.


Time Display starts flashing once the mode is switched.


2. Setting the Clock




The time setting can be adjusted by pressing "Up" and "Down" keys. Fast forward and rewind are available by pressing and holding down either the Up or Down key.


3. Confirming Time Setting




After the clock is adjusted to the current time, press the Enter key to confirm the setting. The time display stops flashing once the setting is finished.




The setting automatically cancels when no panel operation is performed for more than 60 seconds in the Clock Setting Mode. If this occurs, changes made will not be reflected to the setting. If the clock setting is rewound to a time that is earlier than the time when a heating cycle is triggered, the system will start the heating cycle.








SLEEP MODE IS TURNED OFF WHEN ANY BUTTON IS PRESSED (UP, DOWN or ENTER). Sanden Heat Pump – Service Technical Book Page 55 of 64






Block out time Setting Mode


Enter into Commissioning Mode


First option is the Heat Setting


Second option is Temperature Setting–


Press the UP Key to access Block Out Time then Press Enter to access


This mode is used to set the block out time that prevents the heat pump unit operation within the chosen time period.


Block out times are used if the customer has a time of use tariff or wants to take advantage of Solar PV production


'bo' and '00XX' (00 = Out Beginning time, XX = Out end time) are displayed. (Initial setting = 00 o'clock for both start and end)


Adjust set block out Beginning time


Press Up or Down key and '00' (start time) in '00XX' starts flashing and 'XX' (end time) illuminates. Now the block out Beginning time can be adjusted. Setting can be performed only in hour increments, not in minutes. Time is displayed in Military time not AM/PM


Set block out Beginning time


Press the Enter key to set the desired time setting. After the start time is set, the start time display stops flashing. The end time display NOW starts flashing.




Adjust block out end time


Set to the desired end time by using Up and Down keys. Setting can be performed only in hour increments, not in minutes. Time is displayed in Military time not AM/PM


Set block out end time


Press enter key to set the desired time setting. After the end time is set, the start time and end time are displayed for two seconds, then it starts to display 'bo' and '00XX' (00 = start time, XX = end time) sequentially.




Go back to clock display mode


Press Enter key to go back to the clock display mode. It will automatically go back to the clock display mode when no panel operation is performed for more than 60 seconds. Block out time setting mode cannot be set unless the end time setting is confirmed.


Cancel block out setting


To cancel the block out setting, set both beginning and end times to '00'. Setting to other than '00' (01 ~ 23) will be interpreted as a setting error and the end time will flash. Make sure to set both times to '00' when cancelling the block out time setting. Sanden Heat Pump – Service Technical Book Page 58 of 64








To bypass the Block Out Time, simply press the UP key to access the next parameter in the Commissioning menu




Kind Regards






From: David Go <>
Sent: Monday, 2 May 2022 10:08 AM
To: Rheem NZ Service <>
Subject: [EXT]Settings / Warranty question for GAUS-300FQS Rheem / Sanden system




I have a GAUS-300FQS system - and as far as I can tell, it has not been set up for time-of-use control.  As I'm now shifting to a different power plan  I am going to set this up.  I've looked through the installation manual and worked out the basics of how to configure the built in timer, but I have some questions -


1.   Does the timer have a built in RTC (real time clock) - ie how much does it suffer from drift, and, more importantly, will it remember the settings if I have a black out, and if so, for how long (ie minutes, hours, days)?


2.  Can you confirm that the system only allows for 1 block-out setting per day?   Ideally I would like to block out both the morning and evening peak - as it is, I (hopefully) have set this for the evening peak.


3.  I am considering getting a solar system installed, and having changes made to my electrical board.   Can you confirm if it is safe (ie will not damage the equipment or void the warranty) if I replace the above system with an intelligent timer which controls power to the circuit)?


Kind regards,


David Go




(Rheem boiilerplate footer with disclaimers removed for readability)  

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