Daikin Altherma 3 - Pump settings for Open Loop Design

Hello there,

After a short exchange with Glyn in the YouTube comments of his latest video, I decided to repipe my buffer setup in order to effectively bypass it and remove the circulation pump. I have Daikin Altherma 3 Monoblock 8kw (the smaller size one).

I’ve had the system since June, the suppliers were fairly hands off and let me take the lead with my entire installation, its a midway though deep-renovation bungalow in Bournemouth. I was provided with Daikin’s pre-plumbed setup which I was happy with an it comes from the factory set-up with hydraulic separation and a circulation pump for the heating system.

Last night I finally decided to re-pipe the buffer so it now operates as a volumizer only (not that I really need it, but its part of my cylinder so no need to remove it). The only setting I have now changed in the controller is to set the pump to continuous rather than sample, this means as long as the space heating mode is on, it will circulate - even if no additional heat is required. Do you think this is correct? With sample it would only be circulating the system when the heat pump is heating, and when its sampling for temperature.

I run pure weather comp, no room influence, no actuators, no mixing valves, no manifold pumps etc. It was getting pretty good COP (according to the built in interface) before but hopefully this should improve with the new setup.



@jtrent I think you want the pump operation mode to be Request, so that it only runs when there is a demand for heating. I don’t see the point of circulating water continuously, all you’ll be doing is dragging heat to places you don’t really want it when there isn’t a demand for heat, like out through the heat exchanger outside. It’s also a waste of electricity.

Screenshot of the field settings from my older Daikin (EDLQ). ‘2: Request’ is the bold text, and default value.

Thanks for your reply,

I don’t think it’s correct though, I am running pure weather compensation with no internal reference and the option for request isn’t available to me as the control is based on Leaving Water Temp,

Do those who run open loop style systems not have water circulating through their system constantly? The design of this setup relies on the Heat Pump providing the circulation for the entire heating system.


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Sorry, I didn’t pick up the ‘pure’ part of your setup. Yes, you’ll be running the pump continuously. The problem you might get with this is that you might find the property overheat under a couple of scenarios.

  1. The heat pump can’t modulate low enough for the heat demand of the property. Many forums are full of stories where the Daikin only modulates down to about 40% of its output, so in your case a minimum heat output of around 3.2kw.
  2. The house gets significant solar gain, and warms up. The heat pump won’t know this.

Do you have a Daikin controller like the Modoka? It might be a good idea to include that in your control mechanism and run weather compensation with modulation from the indoor temperature.

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I believe these are the sections relating to our Daikins (EDLA models)

I use LWT mode with the following parameter set:


(I turn the heat pump off during milder periods to prevent excessive standby electricity usage )

and also the following parameter:

“Pump limitation to 60% during sampling”

this runs the pump at 60% electrical power input for sampling (more than enough!) and also becomes relevant when it gets to ~7C as the sampling occurs even when “turned off”


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My only concern with running sample mode is that there would be periods of time where my system isn’t being circulated - though I might be getting the wrong end of the stick with how “open loop” design works. The philosophy champion by Heat Geek and others seems to mostly be implemented with Valiant heat pumps - maybe worth looking further into how Vaillant manages this style of design?

I am considering a Madoka! Do want to muddle on with the ‘pure’ set up for now just to see how it works


“Sample” is only relevant when it overshoots the target flow temperature, and is then basically “waiting” to come back “on” again (short cycling).

Hence I turn “off” Space Heating when above ~7C and no real need for heating to occur as this stops the pump and saves a fair bit of electricity.

Below ~7C or so, the system overrides this and samples anyway, presumably to avoid water below 4-5C in the outside unit which is then getting close to freezing and also the ~3C anti-freeze valve limit before they dump the water from the system.

In this cold weather we’ve had under 6C for long periods, “Antifrost” can also confuse matters as even when Space Heating is “off” you can find the heat pump running to bring the water temperature up to avoid dropping too low. Not really enough to heat the house, but just to keep some thermal energy in the system.

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When running in pure WC Vaillant runs the pump between cycles but slows the pump down so it doest waste as much power.


Thanks for the insight, I’ve popped it on sample to try it out for a day,

I will say, with the bufferless setup the heat pump now runs for extended periods of time, which is great but it modulates down the flow rate to very low and it makes setting up the flow meters on the underfloor heating a little awkward, the areas that are set up to have 1L/min or so end up with nearly nothing at this minimum flow rate (around 7L/min).

From what I can tell the Daikin modulates the pump to ensure a specific delta T (5c). I could manually turn the delta T down in order to force it to get its flow up (around 13-15L works really well on my system). This may also just be resolved by completing the house and having every circuit up and running, as the system design is based on the completed project!

I have an ESP32 device coming so will be trying to utilise that for cheap monitoring - should ESPAltherma give me worthwhile data to use on heatpumpmonitor.org?

While you can pull data from the MMI using ESPAltherma you will be reliant on the internal meters in the Daikin unit, Not specific MID certified meters that are tested and reliable to a stated accuracy. It will give you a starting point but personally splashing out for the l3 heat pump bundle was the best investment I made (allowed me to find and identify a number of issues with my setup).

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I concur.

The OEM system is invaluable and worth every penny, I would be lost without it.


That’s great information thank you for sharing. I had been planning on installing the ESP32 device inside my monoblock unit outside - Is there a way to wire it into the MMI itself to get the data though?

I’d like to splash out on metering, but I think our funds would be better put towards the piggy bank for solar PV!

This will allow you to tap right into the p1/p2 lines on the main controller and not touch the outdoor unit. Don’t know if there are many differences between it and ESPAltherma but worth a go.

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This is a great option, though I think for now I’ll continue with the ESPAltherma route as it’s simpler with regards to the ESP32 hardware itself.

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Hello there,

How do you set the outside temperature limit for space heating? The menu I’ve found is “operation range” and the space heating off condition wont let me set it to lower than 14c, I’d like to set it around 12c for a test period