Can I remove a radiator and cap it off without causing boiler trouble

Depends on the piping. Is it a monoflow system or a continuous loop(does the radiater in question directly supply any other radiaters?)

Chrisyboy...

What kind of heating system do you have.. Forced water or steam?

Also, how many pipes going into radiator?

Let us know...

MARK

The real question is why do you want to remove the cap to start with?