Also of note is that when I put the hot water on, this radiator alone
gets hot with it.

Hopefully, this means that the radiator is across the flow and return of the
unzoned pipework before the zone valves. Two things:

1. It could be inline from the boiler. This is very unusual, and would mean
that removing the radiator would prevent the whole system working.

2. The radiator could be acting as a permanent bypass. If you have an S-Plan
system (separate hot water/heating zone valves) with pump overrun, then this
might defeat the overrun system. You may, however, have an alternative
bypass, or the boiler may not require a bypass.

Christian.