New Shower Head Fitted - now only cold water coming out

Please could someone advise;

I have fitted a new Architeckt Toulon Chrome Shower Kit to replace the worn one on a Aquadart Hydroflo shower unit. All the fittings are same dimension etc. But now i only seem to have cold water coming out of the shower head.

If i loosen/remove the new shower head, the water then flows out of the hose at the correct temperature.
I put the old shower head on the new hose and the water runs correctly, put the new one on again and it goes cold again.

Do i need to adjust something? or do you need special shower heads for this system?

I think you will find that the head is very important to make the hydroflo work, the same thing happens with Trevi boost mixer, it has to be the correct head or it won't work.

Thanks cozzmic.

Popped into Focus and got a shower head that does not have variable spray and it works perfick!