I'm no expert so you'll have to wait for one of the other regular contributors to come along and opine on relative merits of the two manufacturers. However, I have just two points....

Firstly, we have a Mitsi (the 8.5kW) and have had no reason at all to fault it. We were originally spec'd with a Vaillant but supply problems meant our installer offered the Mitsi given they had some in stock already, and it's been rock solid so far.

Secondly, both our experience and a recurring theme being bandied about all the time on this forum and elsewhere is that the differences between the different manufacturers' units are in practical terms trivial if you can get an installer who knows what they are doing with the system design and installation. I'm struggling to think of any thread on this forum outlining a nightmare centred around the failings of the unit itself rather than of the design or installation of the overall system.

@majordennisbloodnok many thanks, good to know you've had a good experience with the Mitsubishi pump. I assume you don't have the Mixergy cylinder? 

The design is more important than the unit, unless you want to take advantage of the manufacturers specific controls as opposed to a simple on/off stat or the homely smart stat.

if you want to get the benefits of the homely smart stat then you’d be looking for a unit that homely have done the modbus integration for in which case you’re looking at Samsung or Midea.

@hughf I must confess I have no idea what a "homely stat" is. Also, I am a bit limited to the ASHPs that my installer works with, and they strongly prefer Vaillant and Mitsubishi units. 

Posted by: @kk_777

@hughf I must confess I have no idea what a "homely stat" is. Also, I am a bit limited to the ASHPs that my installer works with, and they strongly prefer Vaillant and Mitsubishi units. 

Homely is a smart thermostat that is specifically designed for ASHP use. It provides full, advanced, weather comp and scheduling from a smart phone app. It automatically sets the weather comp curves up to suit your property location and rad emitter sizing. It's a complete game changer:

https://www.homelyenergy.com/

But if you are stuck with what your installer will fit then go Vaillant - but make sure it's a complete Vaillant package with all their controls, wiring center and thermostat. You'll get sub-standard performance installing a Vaillant without using their balance-of-system components.

Posted by: @kk_777

Hello all, we are considering quotes from our installers for the above ASHPs, with or without a 250l Mixergy tank. I am generally of the impression that the Vaillant pump is better, but it is about £1200 more than the Mitsubishi without the cost of building its own little platform and soakaway in the garden (which I have yet to get a quote for).

Would be most grateful to hear people's views / experiences on:

- The relative merits of Mitsubishi Ecodan vs Vaillant aroTherm - which would you guys choose, taking account of the price differential?  

- I assume the mixergy would definitely be a good add on for the Ecodan, but I haven't seen anyone talk about it in combination with the aroTherm - any thoughts on this combo?

Thanks in advance. 

 

We too have a Mitsubish ASHP and it's been great - good performance and reliability and lots of engineers who know them.  I can't comment on Vaillant, nor do I have a Mixergy tank.

I cannot comment on the relative pros and cons but can tell you I have a Mitsubishi 11.2 ASHP and I’m very pleased with it. My only comment re the Mitsubishi is, if you go that route, to insist that your installer use only Mitsubishi controls.  Mine installed third party wifi stat’ which although it worked it caused confusion.  Third party parts were used due to shortage of supplies, allegedly.  Once changed the system works flawlessly.  Very impressed.  I cannot comment on the Mixergy but remember somebody on this site recommending it to me when I was setting out on my ASHP journey. My installer decided against.  I think some installers are set in their ways re makes and models due to familiarity.  If you get a good install I doubt you’ll regret it. Good luck.

Always go with the manufacturers controls/stats (if you must have a stat - ideally you don't need one)