you can do either of those options. Using the Hive is less efficient than using the Mitsubishi controller. This is because the controller can actually modulate the pump. The Hive is just, as you say, on and off. You can make it more efficient, but you cant ever match the pump controller for what it can do.

I am in the process of having my Nest removed for this exact reason.

Posted by: @brooster

Hi looking for help. I have an ECODAN and am using the Hive stat. The HP is set for temp compensation etc but I know the Hive is just a dumb on/off switch. The ECODAN ought to be able to modulate but is off more than it is on and I suspect this is down to the dumb Hive which was designed for gas boilers after all. Ought I swap the Hive for Mitsubishi’s own stat or ramp up the Hive to say 30 so it’s calling for heat all of the time and then lower the flow temp to achieve balance and get the house temp that way? My installer says it’s fine with Hive as a dumb switch but I can’t get my head around that 

Hi Brooster,

Welcome to the forum. Batalto is perfectly correct that a thermostat is not the ideal method of controlling an ASHP.

The Mitsubishi Controller actually contains a temperature sensor, but needs to be located in the room whose temperature you are trying to control. If the controller is not in the correct location then you could try the following.

Set your Hive 1C or 2C above the desired indoor temperature. Ensure that your heat pump is set for Weather Compensation, and adjust the curve to say 25C Water Flow Temperature at an outdoor temperature of 20C and 45C Water Flow Temperature at an outdoor temperature of -5C.

Monitor your system over a period of time and see how it performs. Make small adjustments to the curve if you deem it necessary.

Your installer is an idiot…

turn the hive all the way up and forget about. Or have it removed altogether. 

if you’ve got an ecodan then it makes sense to use the Mitsubishi room sensor/controller.

Posted by: @brooster

Ought I swap the Hive for Mitsubishi’s own stat or ramp up the Hive to say 30 so it’s calling for heat all of the time and then lower the flow temp to achieve balance and get the house temp that way?

Do you have a Mitsubishi controller too? If so, then there's not really any drawback to adjusting the weather compensation curve until you reach balance.

The Hive may just be intended as a safeguard against overheating if the curve isn't quite correct or the Mitsubishi controller goes crazy after a firmware update (which I have seen happen once). It seems a bit like expensive overkill for a safeguard, though.

Posted by: @derek-m

If the controller is not in the correct location then you could try the following.

If the controller is not in the correct location and is a recent version, it is possible to get another sensor and connect it. Not cheap, though.

Posted by: @hughf

Your installer is an idiot…

turn the hive all the way up and forget about. Or have it removed altogether. 

if you’ve got an ecodan then it makes sense to use the Mitsubishi room sensor/controller.

@hughf

Exactly what I had to do.  Installer put in a Heatmiser stat.  Since replaced with proper Mitsubishi sensor/controller.  All is good since the change.

@morgan to be fair I had no idea on installation and already had the Hive. Installer asked and I said keep the Hive having no understanding of the differences and thinking it would run like a gas boiler! Looks like between all the comments Hive has to go…

@mjr I only have the onboard controller on the hwc but it is in the garage so without something (Hive) there is no way for the ASHP to know what is going on in the house. However from all the comments it looks like (as I suspected) Hive goes and Mitsu’s own wireless stat replaces it to talk to the onboard controller on the HWC

Posted by: @brooster

@morgan to be fair I had no idea on installation and already had the Hive. Installer asked and I said keep the Hive having no understanding of the differences and thinking it would run like a gas boiler! Looks like between all the comments Hive has to go…

@brooster

My installer, although I was insisting on full Mitsubishi control components, suggested his hands were tied due to supply issues.  Now that is partly true as I had to source and buy the required parts myself and there was a delay.  I say partly due because he actually specced Heatmiser in the initial quote.  Once I had possession I called him back post commission and he replaced the components for me.  It was clear however that he wasn't familiar with them as he was on the phone to Mitsubishi tech support being talked through the install.  Basically I think it's just easier for installers to go with a dumb on/off stat as it makes life simpler for them.

@morgan indeed I suspect you’re right. As I understand it to remove the hive and install the Mitsubishi stat there’s a couple of dip switches need changing one to remove a third party stat and others to install the Mitsu stat; probably not for the faint hearted as a diy project…

The Ecodan actually works quite well with 3rd party room stats and weather compensation. Once you've got your compensation curve about right, use the room stats to stop the house overheating, i.e. set them 1-2 degrees above your target (as others have said). This will switch the ASHP off and let the house cool a bit if it gets too hot.  You can also use the rooms stats for setback using their timers.  The only slight issue with this is if you have a well balanced compensation curve it takes a while for your house to heat up after a set back.  But you can tinker with the timings and it works quite well.  It's often said that the ASHP will use a lot of power to heat up from cold.  It doesn't really if you're using external stats because the ASHP doesn't 'know' how cold the house is. It only has to heat up the flow temperature and that doesn't take very long.   

Weather compensation on its own is also good but unfortunately you can't adjust the offset automatically on a timer; it needs to be done manually.

If you use the Mitsubishi room temp setting mode and controller, the controller does 'know' how cold the house is and, depending on the settings, it will try and achieve the target room temperature by boosting the flow above the weather compensation set point.  This could be less efficient   

I've just bought a Mitsubishi wireless controller.   I've got lots of data on energy use with weather compensation (with and without room stats) from my MMSP so once I've got the Mitsubishi controller set up I'll do some logging and comparison and work out which one is best. 🙂 

@kev-m that’s kind of what my installer says but I only have TRVs in each room and from other research I’ve done the advice seems to be to leave them on max and don’t create cold spots as that makes the pump work harder as the emitting area is artificially reduced leaving the pump to work harder to push out the same heat through a smaller available area? TRVs are clearly not as sophisticated as individual stats in each room. That said three rooms face due South and when/if the sun shines they can easily get to 23 with solar gain which kind of throws everything out of whack anyway…