Ice formation brine pipe heat pump

Which brine-water heat pump do you have? How many kW output? It seems that brine and heat pump do not match. Although at 210m you can already connect quite a lot (in poor regions 50W per meter would result in 10kW load). Maybe air in the system due to flushing? Wrong refrigerant?

Had I already written that we have a Viessmann Vitocal 222G with NC Box and 7.54KW output. Originally, a 333G with 10.5KW was offered, but after calculation, this is what it ended up being... No idea if that's correct, we're still a bit in dispute with the company about it...

Since the brine pipe is freezing, it is indeed being used. Just with too little yield, otherwise it wouldn't be in subzero temperatures (our area collector now has about +10 degrees EM at the end of a cycle). Take a look at how long your compressor runs continuously and how often it switches on. I don't know Viessmann, does it have a data logger and can you provide the data from the last few weeks?

Hm series connection. Relatively exotic in my opinion. Has disadvantages in pressure loss = high pump current, maybe the pump is also too weak? Venting is also much more difficult than with a parallel connection. There are special forums for something like this. But I would drag the system installer over, preferably directly with factory service.

It is certainly connected according to Tichelmann; besides the individual connection to a distributor, everything else would really be very exotic. The heat pump with 7-8KW will be enough for your house. Especially when considering solar and other gains. And with heat pumps, overdimensioned = really bad. (Especially with a fixed speed, like yours) Since the spread in the brine circuit according to your values is only 2 degrees, something must be flowing through; otherwise, it would be much higher and your pump would not achieve 15 minutes of runtime but would fail very quickly with an error. Presumably, 1-2 of the probes are not properly vented and the system is practically running on one. This can happen with Tichelmann and is basically more complicated to manage than if the circuits could be shut off individually for venting. Since your machine only knows full throttle, temperatures can drop quickly with such an "artificially" undersized source.

Out of interest, can you post an overview picture of the system? Is there a buffer? What does the pressure in the brine circuit say? Is there a vent at the highest point?

If you are interested in optimizing your system, you should introduce yourself. But don’t be disappointed; they will initially tear your system apart, but they are always willing to get the best out of it.

Vitocal 222G vs Vitocal 333G is ultimately not a question of maximum power. Both classes offer 10kw or also 7-8kw. One modulates, the other is fixed speed. There are actually few reasons to prefer a fixed speed over a modulating one, perhaps except for the price. No idea where the difference was for you.