Is my builder stupid?

Hello,

The builder who installed my pipework was a bit of a bodger, and has given me some advice which I do not think is accurate.

To control the heating in my kitchen/living room/bedroom, each of these three radiators has a smart Tado valve on it. These Tado thermostats work fine. However, the towel radiator in the bathroom is on permanently, and does not have a thermostat. I assume that it’s due to this, that my gas bills are sky high. It’s red hot, all day, every day, even when the Tado thermostats my other radiators are on low. (e.g. 15c).

The builder has told me that I am not to turn off the towel heater in the bathroom under any circumstances as it could damage the boiler. However, I can’t see what harm it could do, as surely the water would just bypass the towel radiator in the bathroom and flow back into the boiler…

The only other thermostat I have (aside from the Tado ones on the three main radiators) is the one built into the Worcester Bosch combi boiler. Because this is so far away from middle of the house, and because I don’t want to heat all rooms simultaneously, it’s not useful.

The two photos attached to this post are ones the builder sent to me, to explain how it’s been set up.

So, my question is, can I turn off all three radiators and the towel radiator at the same time, without running the risk of this causing damage.