well he's shouldn't have unless he's prepared to replace it when it leaks as most do!The engineer, when he came, used the red valve to release water.
again it shouldn'tIt has a hose that goes into a bucket currently - it does not go outside.
see 1st item and make your choice!Can I use the red valve to release water. This valve opens and closes itself when let go. I think it is the pressure release valve.
ideally get a rad valve with a draincock and put in system somewhere.
Combi manufactured in 1924 I'd be very surprised if it was !!