Wet underfloor heating - strange problem

[Stevie5tapes]

2 years ago I had installed wet underfloor heating in my new extension along with a new central heating system in my house. Everything worked fine. Recently had my loft converted with some extra rads installed.

When the cental heating is on all the rads work fine, no problems. When just the underfloor heating is on (and not the rads) the rads get warm but not hot. At first I thought one of the two way valves was not working but when feeling the pipe that feeds the rads at the 2 way valve its stone cold. Iam assuming the return water from the underfloor heating is feeding the rads in reverse?

Before I go back to the plumber has anyone got any advice or experiance in this field? I'm sure its something simple.

Many thanks for any advice recieved.

 

[Boilerman2]

Non- return valve required in radiator circuit return pipe, BEFORE the branch from the underfloor heating

 

[Stevie5tapes]

Non- return valve required in radiator circuit return pipe, BEFORE the branch from the underfloor heating

Many thanks Boilerman2. I thought it would require a non return valve just wanted someone to back up the idea. Now to see what my plumber will say, probabley want some extra money to sort it! lol