Posted by: @m1kegibson

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My daughter has recently moved into a new flat where water and heating are provided by an Ecodan ASHP.

When she moved in I tested the underfloor heating and it all seems to work with the zone valves opening and the ASHP kicking in to circulate water through the manifold/underfloor pipes etc.  So far so good.

What I did notice however is that the hot water did not kick in despite the water in the tank being more than the configured 10 degrees below target.  The Hot Water is set to continuous (not timed).

The engineer looked at the system and after turning off/on, the ASHP kicked in and heated the tank water.  However, after using hot water and the tank temp again dropping below target, the ASHP did not kick in.  The control panel never indicates that the system is demanding the ASHP start up and heat water.  Again, if turned off/on, the heating cycle begins, heats the tank but again never replenishes the hot water.  The engineer has visited 3 times now and nothing has changed.

Does anyone have a clue of what might be happening here?

Mine (Vaillant) recently did something very similar, basically heating DHW for a short while after a reset, then giving up.  It was accompanied by various other 'funnies' which made me get quite concerned that the control unit had thrown a wobbly and would need a new PCB.  

It turned out to be a blocked filter which, my installer tells me, accounts for 90% of his ASHP call outs.  I thought I had cleaned out the filter mysel, but it turns out that I have 2, one magnetic filter (easily accessible and easily flushed) and a second, finer, mesh filter which in my case is just behind the outdoor unit and requires you (or a plumber) to lie awkwardly on your/his/her side to access and clear, having first isolated the filter from the system,

Your symptoms are not identical, but they are quite similar and its a different unit.  That said Im surprised the engineer didn't check water flow rate first of all.

Probably worth checking this. a second filter, if there is one, could be inside or outside the unit.  Are there any error codes.

Thank you for that. I will tell them to check flow rate. As you say that seems schoolboy but given their only suggestion so far is to turn it off and on again that is at least a plausible explanation!

Unfortunately there are no error codes so on the surface everything seems okay. 

Posted by: @m1kegibson

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Thank you for that. I will tell them to check flow rate. As you say that seems schoolboy but given their only suggestion so far is to turn it off and on again that is at least a plausible explanation!

Unfortunately there are no error codes so on the surface everything seems okay. 

Yeah, mine did exactly the same - no error codes.  The turn on/off again suggestion was (sensibly) made by my installer before he turned up - might as well get the obvious out of the way without spending time.

Vaillant has a 'live monitor' function whereby you can monitor various parameters like flow rates etc and also it tells you what its currently doing with a short message (eg 'DHW pre-run, compressor on').  Does Mitsi have anything similar.  It could be in the installer menu and should give an insight - perhaps in this part of the menu tree

The way my installer proved the problem in my case was to whack the water pump up to max (using a 'test' function) and monitor the flow rate, which was half what it was when he first commissioned it - pretty much QED.  Since it took only 3/4 of a 'season' to block up, I intend to learn to do this myself!  I cant really blame the installer for the grot in the system given how old bits of it are.

Heat pumps controllers are, by reputation, more keen to 'check' their operating parameters and stop if they sense anything amiss.  They thus appear more sensitive - boilers by contrast just let the heat exchanger bung up (for example) until they overheat and need replacing!

Of course its worth also double checking the DHW program/settings in case anything has changed.  There is absolutely no guarantee its a filter.

Posted by: @m1kegibson

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What I did notice however is that the hot water did not kick in despite the water in the tank being more than the configured 10 degrees below target.  The Hot Water is set to continuous (not timed).

The engineer looked at the system and after turning off/on, the ASHP kicked in and heated the tank water.  However, after using hot water and the tank temp again dropping below target, the ASHP did not kick in.  The control panel never indicates that the system is demanding the ASHP start up and heat water.  

Hi @m1kegibson 

Maybe a long shot but is the controller in holiday mode? There would be a suitcase symbol towards to top left of the screen if it is. 

Another long shot, is the DHW smart grid setting on? 

What happens if you set it up to do DHW on a schedule? Does that work okay?

To check the flow rate you go into the service menu, scroll down to running information and enter 540. The displayed number is the flow rate in l/min. 

@robs @jamespa Thanks for your input.  I will explore/suggest the engineer looks at flow rates.  The Smart Grid function would appear to be disabled (no SG icon on screen) but will take a look at settings.  When I hit "Heat Now" in the MELCloud App the system kicks in so it does not need a restart to get it to work!  This is very frustrating!

Posted by: @m1kegibson

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@robs @jamespa Thanks for your input.  I will explore/suggest the engineer looks at flow rates.  The Smart Grid function would appear to be disabled (no SG icon on screen) but will take a look at settings.  When I hit "Heat Now" in the MELCloud App the system kicks in so it does not need a restart to get it to work!  This is very frustrating!

If it heats reliably when triggered from melcloud it points more to a control misconfiguration than to anything physical. 

Holiday mode, selecting manual operation rather than timed, or some corruption of the time programme are the obvious ones, but I guess you have checked these already.

I have experienced problems with various soft/firmware devices (including my heat pump) which are resolved by changing a setting then changing it back again.  Might  be worth a try 

It’s definitely not in holiday mode (no suitcase symbol). I think it’s in “constant” mode but not sure I know what “manual” mode is? Can you illuminate?

Posted by: @m1kegibson

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It’s definitely not in holiday mode (no suitcase symbol). I think it’s in “constant” mode but not sure I know what “manual” mode is? Can you illuminate?

By manual I meant constant/DHW priority, ie it should reheat once the temperature drops below (target - hysterisis).  Are you certain (a) the unit has this mode and (B) it is set to this or could it have been turned off with the space heating

The schedule function on the Mitsubishi is potentially confusing as it seems to combine DHW timing with space heating timing.  Is it possible someone has accidentally fiddled with this?

Is it possible that the temperature sensor has become displaced

I presume that the DHW hysterisis is set to a sensible value (10C you seem to say)

If you are absolutely sure that it works every time when triggered from Melcloud then that pretty much rules out anything physical other than a sensor issue. It also sounds like it works once but not repeatedly, which suggests scheduling.

When you say that the water in the tank is more than the configured 10C below target, is this according to the controller or some independent measurement.  What temperature does the controller think the water is at the time it 'fails' to reheat?

What happens if you use 'forced' DHW mode  -some explanations in here

Unfortunately Im not a Mistubishi controller expert and some heat pump controllers can be a bit confusing until you get used to them, albeit in the end the functions are pretty similar.

A couple of pics. One shows temperature of water in tank (report from MELCloud app) over course of 24 hrs water in tank dropping to close to 30C and a pic of the controller confirming water. Tank at 31C but not demanding heat. 

@m1kegibson Hi, looking at the melcloud it looks to me that it stops heating the water at 40 DegC, this is set to low and it will fire into hot water mode when it hit 29 or 30, they often come out the box with a 10 Deg diff, so if set to 40 (Max Lim) it will wait until 30 before it fires up again.

The reason it probably works when reset is the ecodan when first fired up looks to satisfy DHW as it treats this as a priority. This will work regardless of the temp below the set point until set point is reached.

The only reason I can think that the melcloud is saying it is set to 50 but it is stopping at 40 is max set point DHW settings?

Just so you know, the quickest way to fix this if it is a programming error is to call Mitsubishi electric, they will log on through the app and make the settings correctly, they have an amazing customer support and can fix this if it is just installer settings.

Looking at those photos I agree with @ashp-bobba.

To put it another way it looks like its targeting a DHW temp of 40 not 50, which means that it will normally start reheat only when the temp falls below 30 (assuming the default hysteresis of 10).  Reprogramming/correcting the programming is likely the answer.