Citroen Relay Van?

My parntners 54 plate relay has just started overheating (engine) and is losing pressure, it has started to leak water / anti-freeze but cant locate where it is coming from. unfortunately my partners is currently working in Germany where it is -14 degrees - would this be a problem to the van?
Please help to shed some light on what this may be - i thought thermostat? He did take to garage this morning but they couldnt find the fault and sent him away to a garage 20miles away but said he might not make it - helpful i know. If we at least know some of the faults that it could be then we can take to another garage closer and ask them to check pacific problems out. Please help if you can - Kim