Incompetent Installers , incompetent regulation Do I need a MIM-B19N?

HI Christian,

Given the almost three month long fiasco with my “migrating Flow sensor”, I am painfully aware of the Water flow values!

For my system it varies between 16 lpm and 23 lpm depending upon wither it is supplying the Hot water tank coil or the Heat Exchanger/Radiators/Volumiser tank.

The Water flow sensor is still not fitted with the correct cable, seven months since the original Czech Electrical Engineer , Viktor, complained, and refused “to cobble up a cable”.

Viktor gave the international hand signals for “tearing his hair out” when told to Patch a temporary replacement cable in place.

Viktor has since resigned from my “installer” preferring to stay in Brno rather than Glasgow!


Thanks @iantelescope can you provide a link to the exact manual that you are using?

Hi Trystan,

We get a hard copy with the unit but is the Samsung support page for the indoor unit, the Field Settings are in the left-hand download.

@iantelescope can you check the doc in the link is the same as your manual please?


Hi Christian & Trystan,

Yes, I can confirm that this is one of the three Manuals I received.

The Details of the use of field options 2091 options 1 to 4 are given in the manual.

My Heat Pump has resumed intermittently failing to heat my house.

I have now not using Hot Water from the Heat Pump.

I have partially closed the valve to my Volumiser tank, trying to limit , hopefully,instability.

The Symptoms would be consistent with an intermittent Outside Air Thermistor failure.

The Air Thermistor does not seem to have an Error code, and , I can test it by shutting down the Heat Pump and running the outdoor diagnostic. When running the Diagnostic the Thermistor, Address 040 H
shows the correct temperature.

How can I access these outdoor Sensors without an MIM-b15N ?

Where can I get a set of thermistors for the outdoor unit?

A YouTube video showing "how to replace these thermistors " is available, showing such replacements to be a fairly regular occurrence in the much colder USA.

Please don’t advise my , now former , Struck OFF, “installer” OR the MCS, NIC or RECC.

I have had it up to my eyeballs with the “installers” and “Regulators”.


Hi Trystan and Christian,

The You tube video showing the measurement , and replacement of a dead Outdoor Temperature Thermistor is at

My manual does NOT show a E337 Error.

How do I access the Status registers within the outdoor unit ?

Can the MIM-b15N access the Outdoor status registers while the Pump is running?


to Christian & Trystan
Following a morning where the Heat Pump , again , spectacularly failed , with the Water Flow Temperature , again rising to "impossible " values greater than 55 C, I may have , finally, found the cause, if not the solution.

When the Flow water temperature is set and controlled by the Weather compensation system, Field option 2091 options 2, 3 and 4, the Temperature control system can become unstable.

This instability manifests itself in large “Ringing” Flow water Temperature overshoots.

Changing anything within the feedback loop , Hysteresis ( 2091 opts 2,3 or 4) , Switching the volumising tank on or off , rapidly changing the Water Law offset , ALL result in the large Water Temperature overshoots.

The overshoots result in large Flow water temperatures peaks above 55 …65 C! Alarming!!

With Weather compensation controlled by the outside Air Temperature Thermistor , and with the Thermistor being easily replaced , replacing the Air Temperature Thermistor would be my preferred

In the interim I have switched OFF the Weather Compensation control ( Field Control 2091/2092 OFF , 2093 ON with option 2), relying on the Thermistor behind the Samsung Control panel to control the Water Temperature.

So , far, the Heat Pump has remained stable when controlled by the room thermistor.( 2093 opt 2) .

So, I have a "workaround " to get the beast up and running.

How , and where do I get a replacement Air Temperature Thermistor for a Samsung Heat Pump?


Sorry Ian, I don’t know the answers to any of the questions you have asked above.

hi Christian,

Many thanks for your patience.

Could I ask an apparently simple question?

On your Heat Pump front Screen do you use the Flow Water temperature Control screen with the Absolute value of the Flow water temperature, e.g 35 C?
On your Heat Pump front Screen do you use the Relative Water Law version of the Control screen with a +/- 5 C range control, e.g +3 C.?

I have now returned , myself,to the Absolute Flow Water Temperature control screen.

Does anybody , apart from myself, use the +/- % C Work Law relative control?


Hi Ian,

I don’t think I do either of those things!

I set flow temperatures in water law and the heat pump for heating is controlled by an external (smart) thermostat, so a call for heat switches it on.
During winter hot water is done by the HP on relatively cheap electricity overnight; in summer it’s done via spare generation from our solar panels.

A few times in the evolution of this thread I was going to mention you seem to have a slightly unconventional setup, in that I believe you use the thermostat within the wired control unit. I have seen at least 2 heat pump suppliers who say not to do this (on their web pages).
I didn’t mention it because I didn’t think it would help you.
Also, it seems most smart thermostats are not really suitable for heat pumps because they don’t let the heat pump run for long enough. I have bought a more suitable one from the shop here but not fitted it yet.

I have been tempted to try the option where I can set the flow temperature via the wired control unit but I thought I’d probably just get myself in a pickle i.e. I think I would have to change quite a lot of settings to implement it then same again to reverse it when it doesn’t work for me!

Hi Christian,

Again, many thanks for your patience.

Could you send me the details on your smart external Thermostat?

How does your smart Thermostat communicate with the HP?

Given my recent experience I am beginning to fear for my safety.

Who is responsible for the safety of Heat Pumps?

Safety must, surely, not be compromised by the “ability to pay”!


6 posts were split to a new topic: What do you use for a Thermostat

Hi Christian,

Sorry again for the delays …still recovering from my destroyed hard disk on my pc. Did not take a backup!!!

I currently have a simple Honeywell Home Thermostat that interfaces using a simple switch , or relay. The Unit uses a simple radio transmission to control the thermostat relay.

I am considering a continuous , non-switched control.

Samsung provides a “Thermostat Interface” , at great cost.

The Samsung “Thermostat interface” uses the F3/F4 common control lines between the Control box and the Heat Pump in my garden.

This interface converts 240vac to 24 vac Smart Thermostats.

Do I need this unit if using a “smart” European Thermostat?

The Interface unit can also use “Continuous control” of the Heat pump temperature, in contrast to the Switched Thermostats.
A continuous control can provide Voltage or Pulse width control of the Power demanded of the Heat Pump. Not switched , variable.

Does anyone have a continuous control ?


Is your Honeywell’s relay wired into your main indoor control box?

Hi Christian,
Yes it is a simple Radio controlled switch.
Sorry, my Technical authorship has let me down again!

I was considering a continuous power control , not a switched control.

Do I need the Samsung Thermostat convertor to use the F3/F4 control lines?

My Heat pump has remained stable today, but , I am steadily losing confidence after 7 months.


In your posts above I believe I have seen settings which conflict with using the external thermostat.

Please can you share all your settings in section 2, water law?

Hi Christian,

During the last month I have changed the 201* Settings on several occasions trying to control the room Temperature , Heat Pump Economy and Stability.

When cold , and tired, I have increased the Lower settings to 50 C !.
When warmer , and bothered about the Electricity bill I have reduced the Lower settings to as low as 40 C , before regretting this and compromising with 45 C.

Currently the temperature is warm enough that I can survive with head to foot thermal insulation and a lower temperature of 43 C.

The Higher 201 * settings have also been changed from -8 to -5, -5 being my current setting.

When the Heat Pump began overshooting to 65 C I tried to reduce these settings without success!

When unstable, the Weather compensation loses control, probably , I think, because of an intermittent Air Thermistor.

The Reduced Temperature operation during Weather control could also be cause ed by the air Thermistor.

My Temperature measurements are wildly inaccurate due to the K type sensors being attached to the pipes, and not into the water .


Hi Christian,

Yes , I agree , KNX does work but I could never afford it!

I am conscious that I have failed to write about my problems with sufficient clarity.

To Simply matters I have produced the following photographs of the front screen of my Samsung.

Front Screen Without Weather compensation, set using 2091/2092 OFF.

The Water Temperature is set 38 C and the HP is delivering 37.8 C.
The HP is working without Weather Compensation.

Front Screen With Weather compensation, set using 2091 Option 4 .

With the Water Law offset Thermostat set to 1.2 C the Water Temperature is set to 42.4 C.
The HP stays in this condition oscillating about 42.3 C.
Weather Compensation is working

Front Screen With Weather compensation AT peak operating point, set using 2091 Option 4 .

The Samsung is stable operating point at 42.4 C.

Samsung Air Temperature Sensor. The probable Culprit.

The Probable Culprit , the Air Temperature Sensor!

Hopefully, Photographs are worth a thousand words!

Many thanks

Hi Christian,

A Samsung DE-icing with White Steam accompaniment !!

Please have a look at a Samsung Heat Pump "DE-icing incident " finally caught on camera.

and another,

The photographs do not show the steam /Vapour thrown up over my garden!

After the Show of tantrums the Samsung has returned to stability.
The Outside Temperature is +4 C.

Caught on Camera !!

I missed the Steam However!!


Hi Christian,

Have a look at the Power and Absolute Temperature Graphs after the De-Icing Incident.

Power Graph at DE-icing incident

The Power rapidly increases during the incident at 11.15 this morning.

The Absolute Temperature also shows a dramatic Fall at 11.15.

So, The Samsung is DE-icing at an outside Temperature of +4 C.

I have returned all of my settings to their defaults.

I have no intension of following the Outside Temperature manually , without automatic Weather Compensation.

Manual Flow Water Temperature compensation is far too painful.

Automatic Weather Compensation depends upon the stability of the outside Air Temperature Thermostat.

DE-icing is also controlled by the air Temperature Thermistor .

The Air Temperature Thermistor is known to be unstable in the USA, see You tube.


Hi Ian

The white steam you refer to is completely normal, it is water vapour and is a result of the defrost cycle. When the ASHP fan comes back on it pushes the plume out in front of the unit.

Defrost cycles are completely normal and can happen more often when the outdoor temp falls below 4deg, dependant on outdoor humidity level.

With your method of switching heating off overnight, the heat pump is pushed a little harder when it does come back on. This means the coils at the back of your outdoor unit can become colder, attracting more moisture/ frost and causing a defrost cycle more often.

I don’t believe that the thermistor at the rear of your unit will be responsible for controlling your weather compensation. You will likely have another outdoor stat ideally located on a north elevation away from the heat pump to prevent inaccurate readings. Do you know if you have this installed? Christian may be able to advise on what this looks like.

I personally do not use a room thermostat but use the weather compensation only, there is no room influence and i find that, with the WC curve set correctly, the heat pump modulates perfectly well based on the outdoor temperature. My system lowers the WC curve based on the desired temp of the room, rather than taking any influence from the room itself. This allows me to drop the set point over night by around 1degree, enough that the heat pump doesn’t have to work to hard to return to temperature the next day.


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