Minimum valve opening value for individual TRV

[blueznl]

The radiators furthest from the boiler require a much larger valve opening in order to heat up vs the ones nearer the boiler. If I set the requested temperature to 30C for example they heat up fine. However for everyday use where the temperature is just below the requested temperature the valve will not open sufficiently and the radiator won't warm up. I have checked the balancing and ruled out issues there by turning off all other radiators manually.

Is that in the same room, or in different rooms?

[wutr]

The radiators furthest from the boiler require a much larger valve opening in order to heat up vs the ones nearer the boiler. If I set the requested temperature to 30C for example they heat up fine. However for everyday use where the temperature is just below the requested temperature the valve will not open sufficiently and the radiator won't warm up. I have checked the balancing and ruled out issues there by turning off all other radiators manually.

Is that in the same room, or in different rooms?

That's in a different room than the one I'm testing "valve offset" in at the moment, because I use a HomeMatic IP Access Point and I don't want to break what's working. I bought a CCU3 and linked one HmIP-eTRV-B (this is in a separate room that doesn't have issues otherwise) to it.

[blueznl]

I had some experience with this behavior. Here's how I dealt with it:

1. Give each room its own thermostat, if possible. Then link that thermostat to the radiator valves in that room.

(Controlling multiple valves in separate from a central point never works.)

2. INSIDE that room you can use the 'temperature offset' to compensate for the difference between the radiators.

3. The new valve software (for the HM-CC-RT-DN) seriously stinks! I had to go back to 1.4 to get things working again, 1.5 was just a pain, way too nervous, never fully opening, etc. To be honest, I haven't tried 1.5.3 yet, but I'm not going to mess around with my heating system if things work fine

The only thing HomeMatic never seems to recognize are CAL errors. I've send messages to ELV / EQ3 but go no reaction, asked it here on the forum, but nobody can tell me how to pro-actively spot CAL errors on the HM-CC-RT-DN valves

One of the things to check is the behavior of your valves. Create a diagram and check it, to make sure it's not the firmware causing problems.

[wutr]

I had some experience with this behavior. Here's how I dealt with it:
....

Wow that sounds very complicated for something that should be simple IMHO. I had issues with multiple valves per room + wall thermostat, but resetting all devices and teaching them in again seems to have fixed that a while ago.

You could be on to something with temperature offset, but whether or not that will actually help in opening the valve sufficiently, and then closing it enough to stop the heat demand I don't know yet! The HomeMatic IP app has a note per valve saying offset is controlled by the wall thermostat.

[krawiec]

As I understand your valve normally has a range from 0 - 100%.

When you set the offset to e.g. 20 - the new "0" will be open with "20". So next time the valve will heat up and than after a while stop heating it will return to "0"what will be in reality the offset "20".
The App of course will show you still "0".
If it should heat up with e.g. valve 40, in reality it will be +20 = 60 - in the App you still only see 40.

After I tested and it worked, this is my understanding of this function.

Bu this is stupid in my opinion. If the offset means new 0 so the valve will never be closed. The offset should mean new 1% not 0, or there should be a parameter to set the minimal valve opening if the heating is needed. It is overriding the auto adaptation function which should determine when the valve is closed.
Setting a valve to 1% or even 5% is not an effective way to heat up the room. It will maybe work for some flats with central heating systems where you have the hot water in the pipes all the time, but in the individual systems with the boilers it is making troubles as the boilers have a minimal flow of water that allows them to operate efficiently. With the very low flow boiler will, overheat and turn off for a while. When the temperature drops it will start again and the cycle will be repeated.

In the other hand if we set the offset the radiator will never be closed and will overheat the room when other rooms will still need heating.

I have the same filling as wutr with the minimum valve opening. I have also the HmIP-FALMOT-C12 and same problem - it is trying to open the valve on 1% but the water do not flow - and it is even worse because floor heating has a big "lag". I've found on the documentation that FALMOT has the parameter ON_MIN_LEVEL on channel 0, but there is no such parameter in the configuration page of the FALMOT in CCU. Also there is no way to read or write this Data Point using a script. For example dom.GetObject("HmIP-RF.FALMOT_SERIAL:0.ON_MIN_LEVEL") is returning "null" which means that there is no such Data Point. I've tested a lot and found that thru the dom.GetObject method only Data Points marked in the documentation as "Channel state parameters" are accessible thru HM Script. The Data Points from section "Channel configuration parameters" cannot be accessed (or maybe different method should be used - but I didn't found any clue in the documentation and on the Internet).

Edit:

I've set an offset 50% for one of the eTRV in the room where actually the target temperature is set more than 1,5 degree below the actual temperature. The boiler is on but the radiator in this room is cold. So the offset probably is not setting the new "0" position.

But in the CCU3 there is such information:

"If several radiators in one room are operated with a HomeMatic Radiator Thermostat some radiators may heat more than others. In certain cases, some radiators might be hot while others are still cold.
To compensate this, a valve offset can be set for the radiator thermostat that is mounted on the cold radiator. A valve offset of 0% is set in the factory settings."

I'm wondering if this is setting is effective only when there are other eTRV in the same room... but it seams that both valves closes completely when offset of one is set to 50% and the second to 0%.
Maybe a heating group is overriding this setting but there is no offset parameter for heating group.

Regards
Greg

[tomi_cc16]

Ok seems also logic - sorry if I was wrong

[krawiec]

Ok seems also logic - sorry if I was wrong

I think the documentation should be more precise. As here we are trying to find how the offset parameter is working by some experiments.
Also for me the Data Points are unclear - as for the FALMOT there are same configuration Data Points in the documentation - but nothing in WebUI for CCU3 and also they are not accessible via HM Scripts. The same is for other devices.

Interesting is that the same devices are under the Alpha IP name on the market.

Regards
Greg

[tomi_cc16]

Also Silvercrest and WeSmartify

[rizzuh]

I have the same problem, a radiator thermostat (eTRV-2) is requesting heating due to 0.3C lower actual temperature than the target, the valve is open at 12%, but that is not enough for water to flower, so the room remains cold but the boiler is working (turned on via a WHS2). Valves are a few month old, Heimeier Calypso, basically the simplest thermostatic valve from Heimeier

I have the AP, so I cannot control the valve opening percentage at all, only the minimum for heating, which can be set at 10% max.

[wutr]

The more I think about it, and after having used the central heating for another couple of months, the more I struggle to understand the engineering decisions made by HomeMatic for the radiator valves and associated systems. They must have had a reason, but why would you not allow a valve to open to a certain percentage when it is requesting heat from a WHS2 or MIOB? At that point there is no need to mimic a traditional TRV. In fact, a traditional TRV is a compromise to begin with. For the best flow, the radiators need to be balanced properly and then the input (ie. the TRV / HomeMatic valve) opened fully or to such an extent that it doesn't restrict flow. Having the valve opened insufficiently will cause the boiler to cycle way more often than it needs to, and it doesn't heat the room up efficiently.