I've just moved into this house and there is no way to twist these two knobs. How do I shut off this towel heater?
The smooth one is a cover, the valve inside that is for isolating the radiator for maintenance - you remove the cover and inside is essentially the same valve as at the other end, so you can use the knob off that to engage the shaft. The ridged one should be able to turn, but has probably not been moved in years and is siezed through silt and lime. The bathroom towel rail/radiator typically is left on all the time as it can provide a bypass if all the other thermostatically controlled ones have shut off. The one in my parents' house was usually shrouded in enough towels that the bathroom didn't get too hot.