underfloor heating UFH

I am considering installing UFH in a bathroom, the arear to be warmed is 8 square meters my plan is to run the boiler flow pipe (22mm) to two
zone valves one of which runs the whole houses radiators and the other is to run to the bathroom in 22mm where it is reduced to 10mm JG speedfit for the UFH loop and back on to the 22mm return to the boiler.
The boiler is Worcester 28i junior (non condensing) and brand new.
after the pipes are in it is to be tilled
My question is by reducing it to 10mm will this provide sufficient heat
restriction so as I dont have the full heat of the boiler on the floor tiles?
i.e. I dont want to cause them to crack through thermal shock.
I am not a qualified plumber but have a few years of experience in domestic systems
Follow up
I am informed that thermal shock is possible they are ceramic and 11mm thick as for the controls i was thinking that a radaitor valve works on
the principal of closing the lock shield slightly there by reducing the
flow, that is my reason for using 10mm pipe ie the reduction from 22mm to 10mm would severly reduce flow and temperature.
I could very well be wrong! but i hope not.
Thanks for any advice
Martyn
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Here we go...

I don't do metric....

you're going to overheat the floor.

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You need some type of mixing valve to reduce the temp used for the boiler to somewhere around 110f for the floor. Your boiler may be 140 - 185 to hot for radiant heat.
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