I have a switch near my boiler (apt) for turning on my heating, Above that I have a standered switch for heating water only. This system was installed 10 years ago, everything was working, until yesterday my wife turned on switch for hot water only but rads are now heating up. Hope someone can help
If your heating system is anything vaguely like a Honeywell S-plan, It is possible that you have a zone valve stuck open.
I would check the zone valve. Older ones had a small lever whose position indicates if they are closed or open.
If necessary, you can replace the motorized part without undoing the plumbing joints.