Ecodan 8.5kW PUZ-WM85VAA doesn't stay on

[athlonoc]

Hi,

 

I have just tied out for the first time this winter but coming up against a problem.

Heatmiser stat is set to 26 and room is 20

Flame appears on the stat

The FTC6 controller shows the play symbol and after a short while the ASHP icon appears

Check the ASHP outside and it's on.

 

However after about 2 to 3 minutes the ASHP stops. The ASHP symbol disappears on the FTC6, yet the flame on the stat stays on and the play symbol on the FTC6 stays on play.

 

Any thoughts why this might be happening. The stat is next to the RF switch so it's not out of range. Pressure in the system is at 1bar

 

Thanks

Lee 

[JohnMo]

Is it short cycling? Tell us more about your system. Is there a buffer, if so how is it controlled or is just dumb, i.e. does have a thermostat going back to the controller or not?  If you have a buffer the system is basically split into two system.  The heat pump feeding the buffer, the buffer feeding the heating system. They will generally operate independent of each other if controlled by a thermostat. If you don't have a buffer how much of the system is open to the heat pump?

[athlonoc]

I believe I do have a buffer tank

The buffer being a second tank and is much smaller than the main tank? Is that right.

And if yes to buffer then I'm not aware that it is controlled, just the main system.

 

 

 

[JohnMo]

14 minutes ago, athlonoc said:

The buffer being a second tank and is much smaller than the main tank? Is that right

yes

 

Is this the first time you have use for heating? Or has it been in for a while an been ok before?

[athlonoc]

It has been used before and appeared to work ok during last winter although it was only installed from December 22

So this is it's second winter.

 

[athlonoc]

Just a secondary question with the MEL Cloud App.

Both zones (zone 1 and 2) appear to be on indicated by a sun symbol. But all of zone 2 (downstairs UFH) is at room temp so shouldn't be onand isn't according to the FTC6 controller but is according to the Mel Cloud App.

Zone 1 is the upstairs rads and it's this stat that is set to heat upstairs at a higher temp but is cutting out on this occasion.

The app shows two room temps at 22.5 and the set temp at 20. Can you confirm if they should or can override the rooms stats around the house?

 

Reason I ask this is when looking at the summery settings on the FTC6 , page 2 of that menu has two temperature settings -  HRoom1 & HRoom2

These temp settings change when the settings on the app are changed for each zone. So are these independent temp settings from the actual room stats?

[sliderule]

As your MELCloud shows the same 22.5C for both zones, I'm guessing that your room thermostats are not the source of those readings, and the 22.5C is coming from the thermostat inside the little FTC box (mounted on the bigger FTC controls box, near the Hot water cylinder?). If you are on room temperature mode, then the heat pump will be controlled by those temperature readings. Try using the Weather Compensation mode if you are not already, as that will ignore the "room temperature". See YouTube videos on how to adjust. Don't lower the WC curve too much or the HP will cycle on and off frequently (bad). Too high and you will be spending more on electricity. I'm not sure about the settings you show, perhaps you should talk to mitsubishi if you still have a problem.

[GLPinxit]

I wonder if your Ecodan is appearing to 'not stay on' because the outside air temperature is high enough to mean it cannot modulate its output down to the necessary extent. I get the the same thing with mine at OAT around 14C and am currently puzzling over how to mitigate its impact on energy consumption. Looking at my Melcloud graphs, the system is not so much 'not on' as waiting for the circulating water temperature to cool to the point it 'starts' again.

FWIW I am consoling myself that the gently falling temperature graph is an improvement over the frantic cycling of 12 months ago before I reduced the weather compensation curve. And the house feels no less comfortable.