Leaking M3 Footwell

[Foomanchu]

Evening All

I have a little problem with the M3.
I was driving it Christmas Eve and I burnt my foot as boiling coolant forced it's way in to the drivers footwell. I topped up the coolant and limped home.
I called out the RAC this evening and they have confirmed that the coolant pipes are dry within the engine bay but the two pipes entering the car seem to have the problem but what problem is unknown.
I have checked in the past posts and it seems that it could be the heater matrix that has died but what is involved in repairing or replacing it.
Is it a DIY job or should a garage do it.

Can anyone help

Thanks

Lui

[Aleksandar]

Heater matrix or valve, probably matrix.
A diy can surely do it, I'm just taking a break from taking mine off.

[Brianmoooore]

Another coolant pressure cap not changed under recall?

[Aleksandar]

Btw, what's the easiest way of taking it off, I got to the point where I think if I unscrew four little bolts i can remove the valve and then just slide out the matrix, but those 2 rear ones will be very tricky, any easier way?