Identifying this leaking valve

[Hamsternator]

I have found a small leak from a valve on the cold water inlet to my boiler. It is on the boiler side of the main shut off valve for the filling inlet.

I assumed at first glance it was an isolation valve but would have expected a different type of head on it (slotted rather than hex bolt). Is it a non-return valve? Other?

Either way I am assuming that it will need professional replacement.

Thanks in advance. Couple of photos attached.

 

[BlueLoo]

Double check valve?

(similar?) > https://www.screwfix.com/p/double-check-valve-15mm/96336.

You can change that easily yourself tbh.

 

[Madrab]

Double check valve indeed ... you will need to de-pressurise your central heating system before that can be changed.

Ideally you would swap that out for a WRAS approved (Part L) loop.

 

[Hamsternator]

Thanks all, understood. Whilst I understand the theory of draining the system and replacing this valve, with a newborn in the house during winter I can't risk a cock up, so professional it is.

Greatly appreciate the quick responses.