any tips to identify cold inlet to boiler?

[squowse]

problem is the cold in and DHW out pipes have been stolen!
i have had a quick look and couldn't see any markings. does any one have any tips if it is not marked under the cover?
eg how to tell the in and out of the heat exchanger - connections to diverter valve etc;
should there be a non-return check valve inside the case on the cold inlet?
i dare say i will work it out eventually.

 

[stem]

It might help if you tell us the boiler make & model.