Samsung Gen 6 water law - compressor stops always for 3 minutes no matter what

Hi Experts,

Can anyone explain this behavior (I’d call it dumb) in water law a.k.a. weather compensation mode. It looks weird to me because I’ve noticed some strange behavior in this mode. Seems that for any reason the internal logic decides to stop the compressor it is always stopped for 3 minutes and 15 seconds.

For life of me I can’t understand this logic. It’s clear when there is hot outside and demand for home is lower the pump cannot deliver the heat even at lowest power output but why for the god sake it always stops only for 3 minutes and then start again ? Why it is not stopped longer.

Let’s say there is 10C or 15C outside and the minimal pump output is 3KW and the demand for heat is less than 2KW then ofc the pump stops at some time since it can’t transfer more hear to water to satisfy dT. But ALWAYS only for 3 minutes! so it happened that it cycles 6x in an hour like crazy. What a stupid logic. If I see (software logic) that those interval are very short because probably the heat demand is very low and there is hot outside and radiators can’t transfer it then I will keep the compressor of for 15 or 30 minutes so the radiators (water in the system can cold out) and only then start it again so it can run for much longer. But no, Samsung HP will switch it off always for appx. 3 minutes and then it runs for 5 minutes and again it stops for 3 and all over again.

Am I stupid or I’m missing something here? Can someone explain?

When I switch to indoor thermostat mode then it works until desired temperature is reached and wait for and indoor temperature drop by 1C (this is also stupid this hysteresis cannot be changed because 1C is just too much, 0.5C would be much better). So then the pump in warmer weather is off for hours saving electricity.

In weather low no, it is able to cycle 6x in an hour consuming lot of energy for this and of course overheating. I really don’t understand this logic, isn’t there somethin where I can say wait for damn 30 minutes or so when the compressor turn off just because too much heat generated by the pump ?

To me it looks like this weather law mode is useless in warmer weather conditions. It works good until around 3C when there is no need to turn the compressor of and reach desired temperature and then it starts doing these cycles the more often the warmer weather there is.

Seems the only solution is to switch to indoor thermostat regulation and live with this or can I do something else ? Also I’ve noticed that in water law mode the consumption is slightly bigger than in indoor temp mode. Seems in indoor temp the compressor speed can go lower.

Here’s the graph when outside was 7C this night. This cycled only 5x but you can see always 3 minutes. Where is these 3 minutes from and why ?

This is a graph from yesterday when there was similar outside temperature and it hasn’t cycle once during night. It was maintaining a minimal speed and switched only at 1PM. Then it was off until 8PM. I’ve switched to water law mode and this 3 minutes cycling started.

Thanks for isights.

Motor protection/inverter protection

  • startup places high loads on things that then need to cool
  • the needs to be time for refrigerant to settle into a static state so that you don’t cause trouble by smashing liquid refrigerant into things at startup
  • it limits the system to a maximum of 20 starts/hour which will do swear it out prematurely but at least ensures it gets through the warranty period

In short perfectly normal

Why it then restarts so quickly is illogical/part of the rest of the controls. Can’t help there sorry.

Thanks for reply. Yes, this is clear that in case it cannot maintain dT and the difference is low, the compressor stops because the outdoor unit would get overheated but why those stop cycle is always 3:15 minutes I don’t understand. Now the outside temp went to 12C here and this thing is cycling every 10 minutes so 6x in an hour. My water temperature in the system had no chance to drop and it’s cooling down very slow if there is such high temperature outside so I simply don’t understand why the pump does not keep the compressor off for longer. Temperature drop in a room is maybe 1C in 8h now but the pump cycle like crazy. Btw, isn’t 20 start/stop cycle little bit too much ??? This must be extremely energy inefficient.

I’m rather unsatisfied from this water law Samsung’s implementation so seems my only option is switch to indoor thermostat control. I will try to fine tune it that up to 3C and lower outside it will follow equitherm curve and never reached (in normal conditions - no sun e.g.) the target indoor temperature. This way it can simulate water law somehow. And then when there is +5C and above it will heat until target temperature is achieved and then thermostat will turn of the pump.

Not sure if there is better solution for my system. Probably some buffer tank with TRVs could help here ? I don’t know. I think in regime of indoor thermostat the heat pump is heating at minimum power ignoring the temperature set for water law in case this can’t be satisfied. Then the temperature in room is increasing until room thermostat shut down the pump. This would make the best sense. Just a theory for now but I have to validate.

Also what I hate on this Samsung controller it won’t allow to set hysteresis so it’s always 1C which has effect on comfort level. Can’t understand why they did not incorporate this into the software. That unit costs a fortune and does not have this basic settings.

Just maybe a question, isn’t it possible to change the hysteresis with Modbus ?

Hi Michal,

As far as I can see your heat pump is doing exactly what you have asked it to do, heat water to a certain temperature and pump it around your radiators.

It does this until it has to stop and then resumes again at the earliest opportunity.

The problem is that your heat pump and your house are not a good match for each other at warmer outside temperatures.

We all face this to greater or lesser extents.

My own views are that heat pumps are a completely different type of heating to what we have been used to with burning stuff to generate heat.

We have to learn what our new heat sources are capable of and adapt our homes and lifestyles to fit the heat source as much as we can.

I don’t think many heat pumps are so well matched to a home that they can provide just the right amount of heat in all weather conditions and heating requirements.

But you have to give them the best chance and you can only do that by giving your heat pump somewhere for its heat to go, you need bigger radiators and then you will get longer cycles.

That will produce more heat, exactly what you want to run more efficiently, and then you have to find a way to control it.

Some sort of room temperature control is the normal way, once the house is warm enough then the heat production stops.

1c of temperature change seems quite reasonable to me with your Samsung room temperature controller.

The heat pump is always going to cycle when more heat is produced than the radiators can deliver.

The fact that your heat pump cycles so frequently indicates that the heat pump is producing significantly more heat than your radiators can deliver, so either your heat pump is too big/doesn’t have a big enough range of operation and/or your radiators are too small.

It is probably some of both.

Even with a different heat pump you will probably still experience less than optimum performance either through short cycles and/or having to run at higher flow temperatures than you would ideally like to be able to run at.

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TRVs will not help, they will make it worse, you will have even less radiator output for the heat pump to work with.

You need bigger radiators so you can maintain the dT between flow and return.

If you only lose 1c room temperature in 8 hours then maybe you can do like I do, I just run my heat pump for a few hours, then turn it off from the app and then just turn it back on when I want heat again.

My heat pump produces 4kW when I need less than 2kw of heat. I installed massive radiators and control it from my telephone. Its not automatic in any way at all but it works.

Unfortunately, I think at times, we have to bend to fit in with the heat pump, it’s how it is.

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I’ve seen other heat pumps behaving like this, at 6 cycles per hour and short gaps in between. The Coefficient of Performance will likely suffer as the heat pump doesn’t get chance to reach optimal running conditions. Increasing the duration of gaps between cycles would help, but their control systems often don’t support that.

Your heat pump is cycling because the target flow temperature is too low, and the radiators can’t emit the generated heat. Be sure to open all valves to maximise the flow around the system. Raise or flatten the weather compensation curve so the target is higher.

You may be better off with the internal thermostat, letting the flow reach a temperature that balances the heat pump with the radiators, and turning off when the room is warm enough.

Hi Matt,

Thanks for response. I think you are right but which it has some advanced algorithm that the pump sees it’s not able deliver the heat in reasonable time so it will stop the compressor for longer. I understand it has to stop I only don’t understand why it is always stops only for around 3 minutes.

Yeah, it should know that I have probably radiators which are not big enough to give heat quicker s it should probably not cycle every 3 minutes but 10. Problem is that within these 3 minutes the indoor temp did not drop a bit so it’s kind of useless. And there is no buffer tank and I only have 160m2 house with 10x K1 radiators so the water volume is not that big I would say.

You said TRVs will be worse, I fully agree but what about TRVs with 150L buffer tank ? Seems you have similar unit that my Samsung. This is 8KW (but in fact there is same compressor in 14KW unit) and I found the min power input is somewhere around 800W. Think I saw 700W but this is bare minimum.

This hysteresis of 1C is in reality bigger, would say more 1.5C because that Samsung controller is slow. Therefore would be great if we can set hysteresis manually. I was thinking connecting external dummy thermostat where I can set hysteresis on my own. I only don’t know where to connect those cables though :slight_smile: This indoor controller has some pin to connect something but MIM controller also have some terminals.

Exactly Tim. This is also my observation. My radiators are fully open but all K1 types so at such low temps around 30 they are not able to give heat quickly. Here again I would expect from Samsung controller to see this and prolong the cycles.

Thing is at 10C outside I need only 1.8KW of heat while pump is delivering min. 3KW. So not sure if bigger radiators would help here. I could lower the water temp but I’m afraid it would not help with such short cycling or ? I was thinking about TRVs and some buffer tank 100L or 150L. So in case room temp is achieved, TRv close more or less and the heat will be accumulated in buffer tank. Since there is no heat consumption until TRV open this can hold the target water temperature on defined value and the pump can be off for longer. As then TRVs open slowly the heat start to decumulate from buffer tank and after some time the pump starts operates again. Not sure if this would help, just some theory since I’m not expert here.

Yeah, seems at current situation the thermostat is the best option for me. As I wrote to Matt, I want to try to fine unit that under 3C outside it works fully equithermic, and from 5C higher on thermostat. I guess in this case the pump maintains the minimal compressor speed even in case my water law temperature is set lower. It would make the heat in room would increase and thermostat would finally turn it off.

This seems to be the best from both worlds plus pure equithermic regulation is often problem on sunny days.

I saw a product names Homely which is supposed to be for intelligent controlling of heat pump with real weather compensation and from light/temp sensors but it’s available only in UK and few other countries and I’m lacking some better controls over it. The user application is very simply and not sure if this won’t get more issues than with standard controls.

I think you have said before that you have 10 radiators in your house and you indicate k1s?

But I don’t think you have ever told us the capacity?

What is their total output at dT 50c?

The heat pump will only stop for as long as it needs to to resume heating, in that respect it is very good?

By running water law as they call it, you are asking the heat pump to provide water at a set temperature and it will keep doing that until you tell it to stop, I think they all do that, mine certainly does.

The heat pump will never know what it is connected to, it just sees that the water is coming back too hot and stops. You are assuming that it/Samsung should know that the reason for this is that your radiators aren’t big enough.

Bigger radiators will allow you heat pump to run in longer cycles.

A higher flow temperature with your current radiators will help as Tim has said.

Then your next problem starts, you will get too much heat.

That is what you need to manage, there is no way around it.

I know it is harsh, but you will either get short cycles or a house that is too hot.

You are aiming for the impossible. you want the heat pump to run in longer cycles but you don’t want the heat that produces, you can’t win.

A buffer tank will just complicate things, your house still won’t be able to take the heat produced.

You will be much better off focussing on your radiators than unnecessary complications like buffer tanks.

This is your fundamental problem, the heat pump you have produces too much heat at times for your house.

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At this temperature, these radiators will only output 12% of their rated output (in watts), and can’t keep up with the heat pump. Raising the temperature by 10° raises the output to 30%.

If these were replaced with K2s of the same dimensions, they’ll be able to output double the amount heat for the same flow temperature, and the heat pump wouldn’t have to cycle.

Adding a buffer adds complexity to the system, and rarely improves performance. You’ll likely still see cycling as the heat pump tries to keep the buffer hot while the radiators have throttled down.

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Have you hooked up your heat pump to Modbus yet?

One option is to override the heat pump by turning it off between cycles, to increase the “pause” period. I used to do this on my Mitsubishi, and found it did help, but eventually switched back to using the internal thermostat which has proved to be more efficient overall.

It’s restarting after 3 minutes because it’s been asked to restart sooner by some poorly thought through control logic; but the motor protection is preventing it from restarting.

I think control logic is where European designed heat pump products better the AC derived Asian products.

Most of the euro stuff uses integral control (degree-minutes) to decide when to restart rather than a dumb temperature only based control. This prevents short cycling.


I was talking to Panasonic the other day. They seem to do the obvious thing, and the off-cycle pause depends on outside temperature. surely it wont be long before there controls are far more intelligent

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That’s right. 10xK1 + 2 ladder radiators in bathrooms. Capacity at 40/35@21C is 4.75KW. Not sure if you can approximate this to dT 50C? However, I’m running indoor temp at 23C.

I think it stops because at outside temps 10C it still deliver around 3KW of heat and the outlet temperature rises quickly and reach 35C. Then when it stops, this water cool down in couple of minutes to 32C or so and the pump decides to restore operation. Problem is this is in very short time so it’s cycling like crazy. If the pump would let down to cool the water to let’s say 25C then this would take much log time and it would take longer time to heat back at 35C so cycle would be longer. Seems there is low water volume in a system so it cools down quickly. Therefore I was thinking about buffer tank like 150L. Don’t want bigger because I think there could be some pressure issues. It’s somethin about this in manual. But still I need TRVs to close it that case to prevent overheating and I need only the water accumulated in buffer tank is circulating. Don’t know if it makes sense.

But how you will tell it to stop ? In water law you can’t define any indoor temperature so it heats until dT =5 can be maintained. If it decrease and flow can’t be regulated anymore, it stop the compressor. I can’t tell it use this target temp. This is not possible in water law mode. It is possible however if it’s controlled by indoor thermostat. This is the scenario which I will be needed to use most probably since pure water law is not working very well, and also you may have problem if sun is shining into some room or at the attic. House can get overheated easily (as long radiators are capable to dissipate the heat at given flow and temperature).

But how, if I replace radiators for bigger ones I still need the same amount of heat I only get it more quickly right ? So to not overheat I would need to lower the water outlet temperature and I’m where I was before :slight_smile: Pump can run more efficiently, yes, but I’m afraid it won’t help much to cycling. I guess I would need to double or triple water volume to get better results. However, I have no idea how many liters I currently have in the system.

For sure, but you guys are still talking about “indoor” thermostat controlling mode. If you use pure water flow for this Samsung unit it behaves like I’ve described with lot of cycling at higher temperatures because it follows only dT and the given flow temperature. The only irrational thing is it stops intervals are always fixed to ~3 minutes. And this is the problem.

Because, it could work either this way. 5 minutes ON/ 3 minutes off 3x in a row, or more intelligently 15 minutes ON, 10 minutes off for example based on the inlet/outlet water temps. The amount of heat would be the same roughly. Not speaking about that if it starts the cycle it always run on 1.5KW input so this is just stupid. Seems to me here like it’s kind of not very clever regulation here.

Not really if you control by thermostat. Basically with this method you can set flat curve at 55C no matter if it is -10C or +15C outside… Thermostat will turn off the pump when temp is reached and then stops until it decrease by 1C.

Yeah it won’t but it would help with cycling because that water in the buffer would still hot when TRVs are partially or completely closed. But yes, seems thermostatic way is the only option with temps above 5C to prevent extreme cycling.

I have to say this is all very interesting. With boiler you don’t need to care for these things at all lol.

How does the volume of water circulating in your system compare with what Samsung ask for in their manuals?

(they rely on system volume to set cycle time if memory serves)

Who designed and fitted it and what was their control strategy?

Hi Michal,

Are you really trying to run at a flow temperature of around 30c?

I am not sure that you have fully grasped how radiator output drops as the mean flow temperature approaches the room temperature?

Radiators output about 12% of their rated output at dT50c when the dT is only 10c

If your house is 20c and you are trying to run at 30c flow then your radiators need to have a total output of about 25,000w at dT 50c to deliver the 3,000w your heat pump is trying to deliver.

What is your total radiator output at dT50c?

Posts crossed, if you have 4,750w at dT 16c then you have about 22,000w at dT 50c.

How did you work out 4,750w?

They must be very big K1s?

You tell the heat pump to stop on water law by turning the heat pump off, either on a schedule or manually. If you don’t turn it off it will continue to run.

I am also not sure you fully understand the relationship between flow temperatures and heat produced.

Lower flow temperatures on their own don’t give less heat.

Heat produced is a product of dT between flow and return and flow rate.

Depending on emitter capacity, more water flowing at a lower temperature but higher dT can produce more heat than less water flowing at a higher temperature and lower dT.

Water flowing at 20lpm, flow of 34c and return of 26c will produce the same amount of heat as water flowing at 10lpm, flow of 50c and return of 46c.

The flow rate has halved but the dT has doubled, therefore if the emitters can do it you can get the same heat at 34c as you do at 50c.

That is why the biggest emitters, in your case radiators, are desirable, they allow you to run at much lower flower temperatures and much higher efficiency.

If you don’t deliver the heat from the buffer tank to your radiators because they can’t take any more then the buffer tank will get hot to the point where the returning water from the buffer tank is too hot. This will happen just as it is now, the heat still has to go somewhere.

You will always get short cycles or a hot house however you run. The heat pump delivers more heat than you need. If you run on a thermostat then that will prevent the heating cycle starting again too quickly.

When I say short cycle, I mean that your heating cycle won’t last very long, not continuous short cycling multiple times an hour.

Exactly what you want, you need the heat pump to turn off when the house is hot enough, that is what a room thermostat does.

Why do you want to keep the heat pump running if you don’t need or want the heat?

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Hmm, double you say ? OK, ten let’s say I would replace all K1 for K2 same size… So then I would have 2x better output for the same flow temperature… What is the benefits for me besides I can run on lower flow temperatures ? Pump efficiency will increase but the amount of heat stays the same right ? So how it will help with cycling ? E.g. if heat needed is 1.5KW and the pump is giving 3KW at min.

Seems you are on the same with Matt regarding buffer tank, then I would not install it if you are saying it would not help. Seems like replacing all radiators for K2 could double the performance at lower temps, are we sure of this, if this really double ? Then this would cost me around 1000 - 1500 euro so do you think it’s worth it ? T3 would be even better right but those are very bulky and expensive…

This modbus is the next thing I’m looking for. Not sure how it can help me besides monitoring but I like this idea, however, as you said probably indoor temperature controlling would be better. But this is interesting idea, just thinking loud - would it be possible to program it that it will turn the compressor off 0.5C before target indoor temp is reached ? This could overcome the hysteresis issue so the pump would turn off not when decreased TARGET - 1C but instead TARGET - .0.5C for example. I’m pretty fine with this thermostatic option in case I can change the hysteresis since I found 1C is too much for the comfort on this Samsung pump…

Yeah, since some kind of intelligence is missing here :slight_smile: Really. It should recognize that simply stopping every 5 minute when there is high outer temperature is because the heat demand is much lower that pump provided or the readiators are not able to transfer heat so it can somehow prolong the cycle.

Really ? Then seems this Samsung is pretty stupid because it does not consider outdoor temperature at all. When water low kicks in and switch the pump off it stays off for exactly 3 minutes no matter if there is 0C or 20C. The only difference is that at 0 it’s stops only for these 3 minutes and then running for another our and at 20 minutes it runs only 5 mins :slight_smile:

I haven’t find this information in manual but I will check again, maybe I’ve overlooked. There is only min flow rate which is 7 l/m.

Local company who installed it for the first time… They’ve screwed few things so they are going to fix it. E.g. I have low max. flow only 17 l/m - nominal is around 24. They’ve used magentic filter with small valves (3/4 instead of 1"). Then they’ve installed small pump 25-60 while it required at least 25-80 and so one… But these are things which won’t help with this cycling behavior because required flow is already very low for such temperatures.

Not really, I was only trying it and saw that it is even worse hehe. But I tell you how it works for me…

So at temps +3C and bellow there is no issue since my heat losses are exactly what pump is outputting at minimum power. This I’m running around 38C water out and all fine. Problems starts above 5C and it’s cycling more and more with increasing outside temp - this is in pure water law mode ofc. But I can’t change the curve since it would be too hot here if I’m running at 40C at 10C outside you know. I neeed to run exactly at 40C water at 0C. This is working fine.

Yes, partially :slight_smile: Wait sec I will post you a picture one guy calculated for me…

You can see what size they are and what’s the output at 40/35/21C

Yes that’s a problem, I don’t have any schedulers so it simply turns off by itself since dT is very low as radiators are not able to output the heat. It tries to run water at 35C at 10C outside and this is not possible of course so it overheat fast. Again, the problem is that it stops only for 3 minutes no mater outer temperature, if it’s longer I don’t issues with that…

Yeah but still it’s produce too much heat my house demands at that outdoor temperature.

Yeah, but with TRVs closed this heat in buffer won’t be releases so the temperature won’t drop and the pump can stay off for longer…

I want to set it up and not take care about outdoor temps and want to have the best thermal stability indoor as possible…

Yes, you are still talking about thermostat. But in pure water law indoor thermostat is not used and it relies only on heat loses and the curve set by water law. The problem is that the pump always stops for 3 minutes and then starts again no matter what :slight_smile: This is the main problem.


Start with the manuals and do all the design work for them in that case. Sounds like nothing is to be trusted.

The unit relies on a minimum volume of water available in circulation to manage cycling.

If there were say 200 litres running around and around then you wouldn’t have an issue with the time taken to fall from 35 to 32C, or to rise from 32 to 35C, because it would take too long to cycle frequently.

I would guess there isn’t much water in the system or it isn’t all being cycled (low loss header.or four pipe buffer with distortion, auto bypass valve, poorly balanced radiators, or any of the other rookie errors) then you’ll have cycling issues.

A pipe schematic is a good place to begin.

Honestly Michal, I don’t think you can be helped here.

Your heat pump has a minimum heat output, you don’t want it because your house will be too hot. You don’t want to use the room thermostat but you do want the heat pump to run on water law which is continuous operation with a flow temperature set by the temperature outside.

That is only possible if the heat pump modulates low enough to give just enough heat to match the heat loss of your house, your heat pump does not.

With your house and your radiators, that heat pump and a desire to have a comfortable room temperature what you are looking for is impossible.

You need to go back to your installer and discuss your problems, discuss how you would like to heat the house and then find a heat pump and heating system that matches your requirements.

You can’t do what you want to do and no amount of further complication with buffer tanks and trvs will help.

I am sorry to be blunt but I think it is what you need to hear.

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