turn back filter /water leaves boiler goes to radiators turns back to boile?

In my heating system I have a hot water tank in the airing cupboard - next to the hot water tank is a 3 way valve or diverter valve -or mid position valve - hot water comes in and goes either to the radiators or the heating coil in the tank and sometimes shared between the two - it's driven by a small electric motor. After visiting the tank or radiators it returns by pump to the boiler to be re-heated.

I have never heard the expression turn-back filter - I am unaware that the pipework in any heating system is ever fitted with a filter - cleaning it would be a challenge.

It would be best if you said why you need to find your turn back filter - what is wrong with what?

Good luck...

A Nemo
October 2014