Sureflo pump running slow

[Pickygame]

I had an issue with my water pump spluttering and running slow. Did all the usual checks on filter, leaks etc and decided it was the pump. Having changed the pump it runs slow on full cold, runs on for a while when shut off from mix or hot. No air splutter. Now baffled. Any ideas?

 

[Diabalo]

Check the voltage at the pump as you may have a dodgy connection somewhere.