Heater matrix or split pipe?

Hi guys, ive got a 1999 td5 which up until yesterday id had very little trouble from. After driving all day, the car was started up but there was no hot air, only cold. The coolant reservoir was, empty after filling it up and getting home, only a ten minute journey, it was empty again with steam coming from the engine. I looked underneath to see coolant dripping from the area to the rear of the engine. none of the carpets are wet inside. Could this be a split pipe or is it the dreaded heater matrix? I don't know a lot about this stuff and will proberly be putting it in a garage to get sorted but would like to know what the problem might be before getting ripped off

2 pipes at top rear of engine, have been known to rub through and leek!

The matrix is surprisingly robust, but there are two O-rings joining the matrix to the pipes going through the firewall.

In practice, the hoses to those pipes are the ones to check for leaks.

Peter