Boiler make and model: Worcester Greenstar 28i Junior

Central heating thermostat make and model: Honeywell DT92E Wireless Digital Thermostat

Under floor heating thermostat make and model: Siemens RCU10

Issue: would like better control over kitchen under floor heating

Kitchen: has the above electromechanical thermostat, with 2 wires (L and N). Main issue is control... ie; if current temperature is 12c and required temperature is set to 19c... this will activate the ZONE VALVE to on (you can hear it and it starts to warm up). Boiler is set to timed control ie; on from 06:00hrs - 07:30hrs... and 16:40hrs - 22:00hrs.

Q. Why should the ZONE VALVE be OPEN (ie; from 22.00hrs to 06.00hrs, using electricity when not needed (I guess the cost would be minimal) but more importantly I believe will reduce the life expectancy of the valve. Is this normal?

Q. On a few occasions I have also found where the temperature has been met on the thermostat, the ZONE VALVE makes a racket (loud humming / rattling noise valve doesn’t appear to be a branded make like the central heating valve which is a honeywell) once I adjust the thermostat to a temperature below what's been registered on the thermostat the 'click' is heard and the valve stops (so CLOSED)... is this a fault with the thermostat or valve? Would a digital thermostat be better than the above manul type?

Note: heating does work fine when conditions are met ie; boiler on (or timed and thermostat calling for heat

Help!
Tony