Leaking UFH Thermostatic Mixing Valve

[AliMcLeod]

I noticed yesterday that the pressure gauge on my manifold was low (around 0.75 bar) - the UFH been off so its not a like-for-like comparison, but it was around 1.75 bar back in March.

 

I then noticed a very small leak when turning the thermostatic mixing value (I'm trying to work out the best set-up for this house - i'll do a separate post on that). The leak only seems to occur when turning the TMV so its not a critical thing to fix, but would like to get the system pressure back up. What's the right way to do that?

 

I'll try get some pics off my phone to post.

[AliMcLeod]

The second to last (blurry) picture below just shows a drip of water at the bottom of the TMV.