about Vaillant’s TRIVAI, I found this link which explain it quiet well
https://www.sbz-monteur.de/allgemein/schon-mal-was-vom-trivalenz-punkt-gehoert
You also have to configure in the VRC, it’s all well explained in the manual
I just wanted to follow-up on my previous posts on unstable DHW storage temperature readings, in case it helps anyone. At the time I was seeing fairly small fluctuations and I was putting it down to water mixing effects in the tank. However, I now have better monitoring and also saw some occasional, very erratic readings (see below for a nice example!). It was clear that something was wrong. Anyway, I bought a new Vaillant VR10 sensor (£3.99 on eBay) and it fixed the problem!
Has anyone had to adjust the outdoor temp offset on their SensoComfort? I’ve recently moved the VR20 WC sensor close to my emonPi DS18B20 (they were previously on opposite sides of the house so I didn’t think much of a disparity in readings between them). However, the VR20 (according to the Sensocomfort display) underreads the DS18B20 by a good 2 degrees. On the assumption that the DS18B20 is the ‘golden reference’, I adjusted the Sensocomfort offset up by 2, however it doesn’t seem to have moved the apparent outdoor temp on the display. Does it need a reboot to ‘take’? Seems unlikely…
Hi Jim,
Sorry for the late reply.
My COP has dived now along with the weather to around 2.8, with the average outdoor temp over the day being -0.4. Flow temp seems around 35 Deg.
So I am building up notes to get back to my installer with. Amongst the things he agreed to do was a flush, and balance the radiators.
I have just recently learnt however that there is a difference between a flush and a power flush. He may well have flushed the system, but my rads generally are hot at the top and cold at the bottom
Hi Andre,
Sorry for a late response, but thanks for taking the time to answer, much appreciated.
This is a really nice, helpful forum 
Hi Kieron,
I can’t really make sense of your radiator pictures - could you take one from further away and maybe somehow mark the rad if it isn’t self-evident where it is?
They will be warmer at the top but definitely should not be cold at the bottom, especially when flow and return are so close together in temperature. Per se the 1K difference is not a problem and my first thought would be that flow rate is very high, so with the high volume of warm water coming in it can only cool down by 1K. However, as your radiators are not fully hot, another reason would be that the water is not properly distributed through the radiators - hence my request for a wide angle IR picture of your rads.
You could also try taking an IR video if your hardware supports it to record how the warm water distributes through the rad as it comes in, i.e. close the TRV, wait for the rad to cool then open it and record. A time series of images would also do the trick.
Hi Andre,
Took the close photo initially so the colour scale highlighted the cold bottom of the rad more clearly.
Attached are wide angle. Difference between the top and bottom of the rad is around 10+ degrees
Those look quite ok to me to be honest. There is cooling to be expected from top to bottom as the water releases its heat energy into the room. And the warmer water will tend to flow towards the top. I think your measurements of the rad flow and return pipe might be inaccurate - just the heat conduction from the radiator will make it difficult to externally measure the temperature there. I think the radiator balancing might help - you probably need more flow to that big radiator so the temperature drop across it is only 5K and hence its average temperature a bit higher, leading to more heat output. However take this with a grain of salt, my radiators are attached to a UFH manifold and the balancing works differently there.
I won’t answer this directly as I agree with everything Andre has said.
However with respect to your low COP; are you still running on Expanded modulation? I was running in this mode and was getting poor COP (2.5-3.0 ) after the outside temperature dropped to zero ish. I have since changed to Active room modulation and the COP has improved significantly (3.5-4.0) at the same temperature.
Also bear in mind that at this time of year your heat pump will carry out defrost cycles which will drop your COP considerably. These occur when the outside air is close to zero and damp. If the COP you are quoting cover several hours there may be some of these cycles within it.
Example of a defrost cycle shown below
Note: the negative heat and positive electric power leads to a negative COP over this period.
Hi @Kcf
In my opinion, the best way to “balance” the rads is to get each one as close to the same temperature as possible, in it’s midpoint.
So in the rad above, I assume your midpoint is around 33.4 deg. So if any are colder, then open their LOCKSHIELD VALVES by a half a turn and recheck in an hour.
If other rads are fully open, then reduce this one by a half a turn
Rince and repeat
Remember, TRV sides should be fully open
Hi Andre,
So a 10 degree difference between the top of the radiator and the bottom is normal? (Not a leading question, I have no idea/background knowledge but thought it would be closer than that.)
It’s difficult with heat cameras as the colour gradient goes from the lowest to the highest. This is why I go close up, so the full colour gradient is just for the rad, not the cooler surroundings.
Couldn’t upload a video, so took 3 photos as I move in closer. First has a pair of boots hopefully showing that the height is only around 1.5 feet. For the last bit as I move in you can see that the top of the rad is around 32, the bottom around 23 Deg.
Is that normal and in fact the rad does not need a power flush? The temp difference is obvious even when just using your hand.
The 10°C difference across the radiator sounds rather large and suggests limited flow across this radiator.
My understanding was that your unit was a 5kW Arotherm which is running at 860 l/hr. This unit will modulate down to 2kW and up to 7kW.
When running at 2kW (using specific heat formula) the unit will increase the temperature of the water flowing through it by ~2°C. In a system where you are emitting all this heat through the radiators and all rooms are balanced, the temperature loss through each radiator will be ~2°C.
Why the difference between 10°C you’re seeing and this ~2°C? Several possibilities which boil down to restrictions to this radiator or excess flow stealing the flow elsewhere on your system.
The restriction to the radiator is not necessarily something which might be removed by flushing; it might be cause by long pipe runs to this radiator or valves shut in on the radiator.
Hope this provides some help?!
I would agree with @JimR . This to me just points to lower flow across the rad. If there was sludge buildup, the cold spot would be far more pronounced in the bottom.
So you need to open up the LOCKSHIELD VALVE a bit on this, or close others elsewhere on the circuit.
To absolutely prove the point, close all other TRV’s meaning that this is the only open rad on the system, and watch it heat fully (albeit ensuring the lockshield valve is decently open)
I have to say, the FLIR is the right job. I have one myself and I have used it more with my solar system and batteries, but has been invaluable for balancing.
I fully agree with @JimR and @championc - probably you have to increase flow to the radiator. However, probably the coldest rad temperature is not equal to what comes out the return. Also, youve got quite some cold spots below the radiator. The cold air from there could well cool down the rad more. It looks somewhat similar to what my fans under the radiators do - locally cool it down quite a bit.
Using this sensor (VF1) is know to cause overshoot in flow temperature. In UK, Vaillant actively advise people to disconnect this sensor and restart ASHP.
done yeah
Hi @sprajt_88 ,
I’m also hybrid here with a gaz boiler as you know, Now it’s cold, I’d like to test it.
I’ve setting TRIVAI under 1 via the tariff, the heat pump stops in standby mode, but even after 20 minutes, the gas boiler doesn’t start.
Same thing with the bivalence setting. test at -2.5°C outside, Heat. biv. point at 3° & Alt. point on 0. No start of the gas boiler. Any idea ? could you share your settings ? maybe I’m missing something.
Thanks
https://drive.google.com/drive/folders/1-eqngGhbSK6Sw2hXXR9lHGtd_4rViNY2?usp=drive_link
Hi all,
Not sure whether this the right spot to ask, but I tried to plot a heatpump circle in a Propane log P H diagram. Came up with the following:
a different working point is: compressor inlet 5.7C/4.6 bar, compressor outlet 33.2 C/10.3Bar, Condensor outlet 31.4C, EEV outlet 10.9 C, Air intake temp 7.3C.
low relative pressure of 4.6 bar, 5.6 absolute, should give 6-7C boiling temperature, which could be consistent with compressor inlet and air intake temperatures. However, I do not understand the EEV outlet temperature to be so high. After expansion it would be impossible to have a temperature above boiling temperature I would think.
I hope somebody knows what I am missing, should the EEV outlet temperature not be lower?
For sure the EEV outlet will be mixed phase, as you show on your PH diagram. I’d expect the pressure drop in the evaporator to be only a fraction of a bar (not the ~2bar suggested by the EEV outlet temperature), so at least one of your instruments (compressor suction pressure and/or EEV outlet temperature) must be misreading (or else there’s something in your R290 that’s affecting its vapour pressure, like oil carryover if your compressor is continuously lubricated).
One word of caution when analysing the refrigerant circuit - the evaporator exit (i.e. compressor suction) may be superheated by a few degC, so you can’t guarantee that it will lie on the saturation curve on the PH diagram.
Sarah
In this very mild weather my newly installed 7kW Vaillant is cycling, not surprisingly. Its a straightforward system, no buffer, phe etc, just heat pump to diverter valve to rads/cylinder.
There are two features of the behaviour I wasn’t expecting:
The latter in particular is a bit annoying as it gets noisy at this point. I have enabled quiet mode to cap the compressor speed for now, but since it doesnt need to run at full speed in these conditions, that seems a bit silly.
Do others experience either or both of these behaviours?
Thanks in anticipation for any insight
