Coolant leak

Just running the engine up after putting a new carb on and noticed a small coolant leak from the thing next to the thermostat housing as pictured. Could someone enlighten me to what purpose this thing serves?! It appears to be solid metal so is it replace rather than repair? Thanks

heater valve ,it allows hot coolant to circulate around heater matrix or not

New heater valve needed, I think about £15

Ahhhh that makes perfect sense now thanks for the replies

I think price nearer £25 I have removed mine and used a 3/8 to 1/4 BSP reducing bush and a piece of 1/4 BSP pipe and 90 degree bend to connect the hose direct. You only get heat with the blower on due to no ram effect so not a problem. Run like that for years, if you do drain the system take the opportunity to give the heater matrix a good flush out it can transform the amount of heat.