Technically he is correct providing every radiator has a TRV fitted and a By-Pass is incorporated but this will increases the stress on the boiler and will increase running cost's and will have a shorter lifespan. The best systems have a room stat fitted near the main living area and only have TRV's fitted in bedrooms and south facing rooms, this will allow the boiler to rest when the house is warm and will reduce ware & tear also reducing fuel bills. The best control for combination boilers is a programmable room thermostat then no other time clock is needed