ᐅ Avoid Freezing of the Underfloor Heating System

Hello,

We have a new build that is currently being prepared for leveling compound. We were advised to turn off the underfloor heating because that is a requirement for the leveling compound. It has been off since Saturday. However, we are expecting temperatures around -4 to -5 degrees Celsius (24 to 23 degrees Fahrenheit) in the coming days, and I am worried it might freeze. Our contractor suggested that I should heat the rooms where no leveling compound will be applied, but keep the rooms with the compound cold. Regardless of whether partial heating is good for the compound... is it enough to heat only half of the rooms to prevent freezing? We built on a concrete slab and right now the indoor temperature is already down to 9 degrees Celsius (48 degrees Fahrenheit).

So, our new build does not have underfloor heating yet and is also not completely airtight. Currently, we are only heating with an external heater. For the last two weeks, we haven't heated at all, yet the temperature inside is still 8°C (46°F). So I think it will maintain warmth for quite some time. Could you maybe heat up the place again before applying the leveling compound?
And what processing temperature does the leveling compound require?

Processing temperature 5 to 25 degrees Celsius (41 to 77 degrees Fahrenheit). I still need to talk to our tiler; he has already waterproofed and primed the first rooms.
I closed the red valve on Saturday. The red valve shows about 11 degrees Celsius (52 degrees Fahrenheit), the blue valve about 15 degrees Celsius (59 degrees Fahrenheit). Inside the house, it was still 8.8 degrees Celsius (48 degrees Fahrenheit) earlier.

According to the weather forecast, it will be -1 degrees Celsius (30 degrees Fahrenheit) tonight and tomorrow night, and -4 degrees Celsius (25 degrees Fahrenheit) on Friday night. Daytime temperatures will be just above freezing. It is expected to warm up again from Saturday.

Isn't it possible to set a supply temperature of 10 degrees Celsius (50°F) on a heat pump? That would be like not heating at all.

After some research, it seems that you set the return temperature, and the system automatically adjusts the supply temperature. If I turn the system off, the frost protection mode should be active, which should maintain a return temperature of 15°C (59°F). However, I’m not sure if that might still be too high for the screed. After all, it’s often stated (at least online) that the system should be off, not just turned down. :/

In any case, the return temperature was just 8.4°C (47°F) recently. The good thing is, I’ve read so much that I already know our heating system is completely misconfigured. But I actually expected that—it was clear that it wouldn't be working properly either.

For the water in the underfloor pipes to freeze, it must be significantly colder than -4°C (25°F) for several days, and it must not warm above freezing during the day due to sunlight. Since leveling compound can also be applied in summer, it does not cause any issues if the underfloor heating operates at a low temperature.