@jamespa 

Again sorry James, My Thermostat Only goes up to 25 C , no further.

The Thermostat , delivered by my then "installer " some three weeks after the start of the "installation", with my "installer" initially  not "realising" that a Thermostat was required !.

The version of my Thermostat, has , significantly only Cycle times of 3,6, or 12 Cycles per hour , with the instruction leaflet claiming a once per hour setting. Different Versions?

I will, as you say, have a careful  go at Shorting the Thermostat input pins.

Posted by: @iantelescope

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Different Versions?

Maybe

Posted by: @iantelescope

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I will, as you say, have a careful  go at Shorting the Thermostat input pins.

This will of course cause your secondary pump to run continuously.  However don't worry about this for now as it will also allow us to see what the heat pump is doing without interference from another, totally unsuitable, control loop.

Eventually the thermostat needs to go, as you have now proved, more or less, that it cant even be used as a temperature limiter.   

There are several options (not dissimilar to those that existed when you were going to replumb).  The secondary motor should probably be arranged to run at the same time as the primary motor runs.  But that's a decision for a few days time once we know what the heat pump itself does!

PS to above.  I think you said you had a valve that allowed the buffer to be isolated.  If so I strongly suggest you isolate it. You wont be defrosting at this time of year and isolating it reduces the unknowns.

Also its not the input terminals of your thermostat that need shorting out, its (presumably) live to the output (so the output is live as if the thermostat were on).  You may need to check the manual and, as @derek-m says, be careful.

if you do both of these you will end up with secondary pump permanently on, buffer and thermostat out of circuit, so you basically have a simple system connected by a heat exchanger.  That will give some hope of getting to some sort of optimum settings because it will be possible to see what the heat pump is doing.  Later control for the secondary pump and some sort of temperature sensor can be reintroduced.  Im around for the next few days so happy to give my advice, but only if its followed.

PPS

Please can you confirm how the valves valve1 and valve 2 are controlled.  I presume its directly from the heat pump NOT from the thermostat, but its worth checking

PPPS

Your thermostat appears to feature a programmable upper limit, which limits the max temp it can be set to.  Im guessing that it is this upper limit which is preventing you set a temp above 25C

You can try changing that to avoid having to short the terminals, then set the set temp to 30or even 35.  Manual attached.

@jamespa  I  have slightly lost the plot regarding what the aim of further testing is, now that the planned reconfiguration is unlikely to happen. However, the simplest way to get rid of the action of the external thermostat is to set FSV 2091 & 2092 to 0 (Not use) and turn the set temperature on the wired remote controller up to a high number eg 30C. Ian can experiment with different settings for FSV 2093. If he wishes to change the LWT on the fly, then he will need to go into service mode each time and adjust 2021/2022 & 2031/2032 - as the Offset will no longer be visible in the display.

If FSV 2091 & 2092 are not set to 0, then physically removing the external thermostat wiring will prevent the heat pump from starting up - not helpful! However, there is a workaround, which was used on my system, when my buffer and external thermostat were removed last year. Simply connect terminal B20 (Output Thermostat Power Fused live) to B22 (Input Command Signal Zone 1 Heating Switched Live) as in the picture. This makes terminal B22 permanently live as if an external thermostat was constantly calling for heat. Obviously, make sure all power is switched off first! However, I have a feeling that his external thermostat is required to make the secondary pump work, so removing the external thermostat wiring may cause new problems.

Posted by: @mike-h

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I  have slightly lost the plot regarding what the aim of further testing is, now that the planned reconfiguration is unlikely to happen.

The aim is to get as sensibly a working system as possible without the reconfiguration, step by step.  Currently the system works even worse than is necessary due to the cycling caused by the unsuitable thermostat and the configuration of the buffer (which I think can be valved out).

Posted by: @mike-h

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However, the simplest way to get rid of the action of the external thermostat is to set FSV 2091 & 2092 to 0 (Not use) and turn the set temperature on the wired remote controller up to a high number eg 30C

Agreed but @iantelescope is saying that he cant turn it up above 25C (which I think is because it features a programmed limit that has obviously been set by the installer) hence do something else to make it look like the thermostat is permanently on (there are various options I agree).

Posted by: @mike-h

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However, I have a feeling that his external thermostat is required to make the secondary pump work, so removing the external thermostat wiring may cause new problems

Correct, see above.  

So far as I can determine the rad pump is driven by the thermostat.  Its actually unclear whether the thermostat is also connected electrically to the heat pump, my guess is not but I dont know for certain.  (I will probably ask for a circuit diagram soon!)

If for now we disable the second thermostat (either by turning it well up or wiring it permanently on) we can see what the heat pump does when left to control itself (which currently we cant). 

Most likely the next step after that will be to transfer rad pump control to the heat pump (which has an output specifically for the purpose) and either replace the thermostat with a suitable one, not bother with a thermostat at all, or use the internal temperature sensor of the controller.  Also re-optimise weather compensation.  But one step at a time!

I'm not actually sure whether @iantelescope is following or has lost interest; only time will tell.

Posted by: @jamespa

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Posted by: @mike-h

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However, the simplest way to get rid of the action of the external thermostat is to set FSV 2091 & 2092 to 0 (Not use) and turn the set temperature on the wired remote controller up to a high number eg 30C

 

 

Agreed but @iantelescope is saying that he cant turn it up above 25C (which I think is because it features a programmed limit that has obviously been set by the installer) hence do something else to make it look like the thermostat is permanently on (there are various options I agree).

I thought it was his external stat that he couldn't turn up above 25C - setting FSV 2091 & 2092 to 0 (not use) means that he will be using the Samsung internal stat on the wired remote controller to call for heat. The fact that it is in a poor location doesn't matter in this scenario if we are asking him to turn it up to 30C

Posted by: @mike-h

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I thought it was his external stat that he couldn't turn up above 25C - setting FSV 2091 & 2092 to 0 (not use) means that he will be using the Samsung internal stat on the wired remote controller to call for heat. The fact that it is in a poor location doesn't matter in this scenario if we are asking him to turn it up to 30C

It is but...

Its not the call for heat (to the heat pump) that is the problem, as far as I can see (or at least its not the sole problem).  Its the fact that the external stat cycles the radiator pump which Ian tells us is controlled by it, thus inevitably causing the heat pump to cycle.  Assuming its connected as I understand it to be connected, based on what @iantelescope has told us, that cant be disabled through the FSVs.  Thus the external stat needs to be well above the target temperature, far enough above that its 'clever' modulation function doesn't get triggered.  But whether the external stat controls the rad pump or both the rad pump and heat pump (and however it does it)  setting it way above the target temperature will make it permanently on, removing its 'clever' modulation function.

The internal sensor/control wont have the modulation-cycling problem (because its designed for the application), so I'm not so bothered about this for now.  Once the rad pump is going continuously we can find out if the external stat is also connected to the heat pump call for heat, and if necessary quickly disable that part of its function (if it exists) using the fsvs.

I fundamentally agree that there are several ways to go about this, but as Ian appears reluctant to change things, asking him initially only to adjust controls seems sensible.  Once the adjustments prove what is believed to be the case, then changes can be made with confidence.  I thought it would be a simple matter to ask him to turn the external stat up, but even that has proved troublesome and two and a half days later either isn't done or isn't reported.

TBH I'm beginning to lose patience.  I'm not actually sure whether @iantelescope actually wants help, or whether he just wants to tell people about his problem.  He keeps telling me and others that he is grateful for the advice, but seems reluctant to take it. I'm also not clear how urgent he views fixing it.

@mike-h and @jamespa

E121 Noise on Internal Sensor.

When using the Internal Sensor, just to be clear the Thermistor located behind my Samsung LCD Screen I intermittently get :

On being shown to a Visiting French Samsung Engineer , I , and two other Engineers from my then "installer" were instructed that :

"this is well known problem with the Internal Sensor  caused by noise on the Sensor ".

The Noise was caused by the "External Sensor port being left open circuit when no external sensor was used.

The E121 error indicates that either the sensor is "open circuit " or "short circuited.

I Still get E121 Errors at the start and intermittently during operation.

I , consequently have , from the very beginning some two years ago NOT used the internal sensor.

I have thought about buying the External kit which uses the  same Thermistor as that used on the back of the LCD screen attached to a 12 M cable.

I have been  using the Physical Honeywell Thermostat with Field bits 2091 set to  options 3 or 4, giving the Water Law screen:

Last night , I set the Physical Honeywell Thermostat to 25 C , the maximum allowed on this Thermostat.

I then adjusted the Offset on the Water Law screen to -2 C.

The Physical Thermostat eventually stabilised at 22 C resulting in the following Power graphs :

 The Run time as set by the Physical Honeywell Thermostat varies with the proximity to the desired Set Temperature 25 C.

The Run time is between 4.4 and 4.5 minutes.

This Run time could , presumably,  be interpreted as a cycle time , a cycle time well short of the advised Cycle time of 20 to 30 minutes ( DECC Report).

My Conclusion is that the Honeywell home Thermostat is NOT Suitable.

I have looked at the "homely" offering , but am increasingly skeptical.

A "home made" Thermostat attached to the Samsung MIM-B19N Mod bus Samsung Heat Pump interface is of interest.

Noted.  Is the cycling/run time you now see due to the thermostat or heat pump (or don't you know)?.

If its due to the thermostat please note my post above which suggests that the upper limit of 25 is in fact an installer setting which you could change.

@iantelescope 

Sorry to hear about your issues. You must be in Scotland.
Where are you located?  
I am working with another customer who has a similar issue to you with their install and is trying to get RECC acknowledge the problem. 
I am based just outside Inverness if you are nearby I can take a look.