Thanks for the replies,
Not sure if it's a safety feature but our mixer won't do hot only - i seems to mix cold with it. However, I tried the "turning it to full ho and lowering the shower head". Result - no spluttering, just powered cold water. As I said you can have a perfect temperature shower as long as yo don't want it powered. As soon as you throw the switch for the pump it turns cold.
Any more thoughts?
Thanks Jonatha
-- jonathan