I have a brand new combi shower and the water is freezing cold, I have just replaced it as I thought it was the shower that was broken, I have hot water for the bath and sink, but cold in the shower.The shower is connected to the hot and cold water under the bath but I have hot water in the bath tap ?
Any advise please.

Some shower valves have a screwdriver stop located next to the supply line connection. If the hot side was shut off that would cause your problem. If there's no shut off the shut the water off to the valve, open it up and remove the cartridge and check the inlet ports for trash. Now turn the hot water back on to flush out the supply and valve body. Reassemble and test. Good luck, Tom

Hi Tom
Thanks for the quik reply, If it helps it is a Gainsborough ambassdor manual combi shower where it has a direct feed from the hot and cold conections under the bath. All that is in the unit when you open it is a stat, if I turn the hot bath tap on low and the shower on full (hotest mark)the water is warm.May seem a bit confusing but if I turn the bath hot tap off the shower goes back to freezing water again.

Just an update, The shower is now working, Why I do not know.

Just an update, The shower is now working, Why I do not know.
Just enjoy it and let me know if it acts up again. In the meantime happy showering and rub-a-dub.
Cheers, Tom