Shower mixer problem and radiator problem

Hi people. My first post after finding this site. Been reading through but can't find anything on my 2 probs!

1) One of my radiators (for some reason only the upstairs rad in my bedroom) keeps getting cold near the top. So I am thinking air is obviously getting in to it. I have seen auto radiator venters in DIY shops and was thinking of getting one. What I am wondering though, is, if air keeps getting into this radiator, there must be a problem, and will an auto venter cure this, or do I need to find the problem to prevent serious damage? Air is bad I have heard in a central heating system/radiator, but is it OK as long as it is removed quickly?

2) My shower is not very warm, actually virtually cold. It is a wheel mixer type. Not thermostat if that makes a difference? It is fed by a hot water tank behind it in the airing cupboard, and also from a cold pipe from the tank in the loft. How can I fix this and why is it happening? All other hot taps in my bathroom and in the kitchen are good.

The constant build up of air in the sytem may be due to a reaction taking place between the diferent types of metal in the system. This can be prevented by draining and refilling with the addition of an inhihibitor such as Fernox or Sentinel.

thanks for replying. the thing is though, the system already has sentinel x100 in it (over 2 years ago) and on top of that, only the one radiator is being affected. so it makes no sense!

HI


need more info on sytem.eg, boiler make,model and shower make, type.

boiler is a potterton flamingo.

shower is a aqualisa. white wheel type, surface mounted with pipes jojning behind tiled wall which backs onto airing cupboard. it is a mixer type. not a thermostatic one though.

HI

need new cartridge for the shower

new cartridge? why's that what would that do? sorry if i am sounding ignorant! how do i change it/? can i get them from screwfix/b and q/wickes? or are they specific types for different make showers?

no one