My room thermostat seems to be working but it does not switch the boiler on and off. I have dismantled it and everything looks OK and it switches the connection on and off, but it will not switch the radiators off even when set at zero. They are constantly on. This is a major problem as it now getting towards summer. The boiler control box does not have separate water and heating controls, so when the timer is on I constantly have the radiators on. If I switch off the boiler control then I have no hot water! Anyone got any ideas?