Floor heating

There are numerous ways, two of which were described above. With the flows I posted you can count how many of B though E are on. Then you can make a simple flows: when the count changes, and count is 0 set A true with delay. And another, when count changes, and count is not 0, and A is still on, turn it off with a delay.

Or you can take the group app, put B through E in a group, and then make two flows: when group turns on then turn A off with a delay, and another: when group turns off then turn A on with a delay.

It is a bit hard to build sample flows at my end because I do not have a similar situation, but there are plenty of samples around here on how to use timers. For the group app, look here: