Well your just going to to have to get a 3D solid metal printer 
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I use these on a couple of my rads via sonoff. They work well
Those are for thermostatic valves.
Did you print it solid? or with an infill? Where did it break?
I don't think so, they are on/off valves controlled by the applied voltage, however I think they work by heating wax which melts and the expansion/contraction is used to drive the valve. This means they are very slow (3 minutes in the spec) so they are not ideal if you are looking for good control. It does not rule them out but means you cannot do just a short pulse of heat to keep a radiator just warm.
The documentation on amazon shows that it pushes in a piston and states that it is for thermostatic valve. mine needs to turn, plus mine has a weird mounting point.
@bakman2, would a heavy duty servo work?, it would give you finer control too.
That means that it is for a valve that is compatible with a thermostatic valve head. You are right that it doesn't do what you want as you need a rotary drive.
One of the issues is that you need a spring somewhere in the system so that the drive can 'overdrive' it closed and the spring will absorb the excess travel.
Good point Colin. Now if every house had a supply of compressed air it would be much easier 
Though actually, having said that, some of the commercial products use a low power geared stepper motor that is just driven till it stalls and is left stalled while the valve is open, then has a spring which unwinds it when the power is switched off and closes the valve. These ones, for example, work like that. They need a valve that opens/closes in 90 degrees or thereabouts.
Ah yes, have one in the airing cupboard controlling the diverter valve.
That is exactly how my valve now works.
@zenofmud yes 100% infill, problem is that the moint point also gets very hot so every time it opens/closes, more wiggleroom gets added. Metal will be the only solution.
Maybe a metal inlay into the printed piece??
No chance of adapting a standard spanner / Wrench?
Yes i have to find one that fits nicely in the right angle.
