Rhythmic clicking in the heating circuit distributor of the underfloor heating

Flow and return reversed. In a heating circuit.

Is there a way to find this out without digging up the ground

Unfortunately, I have no idea.

The cracking occurs directly one after the other, otherwise it is independent of day/time. So it can be at 6 a.m., at 9 a.m., and at 8 p.m. So rather at intervals of hours than at intervals of minutes.

Presumably whenever the heat pump is heating. Unfortunately, the link to the file is gone.

I strongly assume that you do not have a heating buffer tank. The thermal cracking you hear (thermal cracking occurs when materials expand and contract due to relatively large/rapid temperature differences) always happens when the heat pump has heated the domestic hot water. What happens is the following:

The 3-way valve switches to domestic hot water, the heat pump heats the heating water to 50-60°C, at some point the domestic hot water is warm, the 3-way valve switches back to the heating circuits. However, the little residual water in the few meters of return and supply pipes from the heat pump to the 3-way valve is still 50-60°C. This water is then pushed into the heating circuits. A floor heating system only needs <30°C. This means that a few liters of water, which are suddenly 30°C hotter than necessary, flow in briefly. This causes the thermal cracking in the distributors.

That’s why it only happens during the heating season. Because only then is the circulating pump running in heating mode. In summer, the circulating pump is off and the hot water does not reach the distributors.

How do I know this? Because I have this too, and it started exactly after I removed my heating buffer tank for efficiency reasons (it reduced electricity consumption by about 10%, but resulted in thermal cracking for about 1 minute every 10 hours). (We do not have actuators, but I balanced it hydraulically myself.)

With a heating buffer, the several hundred liters that would be inside it would simply cushion this, and the hot water would not even reach the distributors.

You can mitigate this if you optimize your domestic hot water heating (so it heats less frequently or only at times when the cracking does not bother you). Or if you lower the domestic hot water temperature, then the heating water will also be cooler.