shower pump squeals!

ive just installed a new bristan varispeed water pump 50 for the shower,i used the exsisting pipe work and it dident take long,i ran the shower up and it worked fine for a few minutes and then the pump started to make a lound screech noise and the hot disapeared along with the pressure.any ideas ?
also i had to change a washer in the hot water tap in bathroom,but i had to drain tank as no stop cock in between tap and tank,ive hade low pressure in hot taps ever since!

some kind of blocage in the pipework....

could be muck/debri in the tank has partially blocked the outlet pipe.

have u had a look?.

To stop hot water flow from taps, one usually closes a valve on the cold supply to the hot tank. (Assuming vented hot tank replenished from cold cistern at higher level). Stop valve not always fitted.
The shower pump has possibly got a slug of air that needs bleeding.
You may find vents at high-points on the pipes to the pump. Failing that, you may have to slacken connections until air-free water flows. Old towels needed and avoid flooding live electrics.