Underfloor heating leak, low boiler pressure

[Notadomesticgoddess]

Hi hope someone can help me with some advice before I call someone out. We have Uponor underfloor heating with a pump upstairs & one downstairs. Each room has a separate thermostat to control heat. We have an oil boiler which keeps dropping pressure but is not locking out. Heating & hot water are working (touch wood!). The upstairs pump I have heard loud clanking noises from & when I look at the pipes as marked on the photo (1) is wet & the other (2) seems to be leaking quite a bit & the carpet is wet so could have been going on a while. Could this be the cause of the low pressure? Does anyone know what this part is & what it does? Thanks

 

[ianmcd]

They are automatic air vents and they leak for fun, screw the red caps down to stop them leaking and then get someone in to replace them