Set fire to it and claim the insurance
 

Ok all the evidence points towards a blocked heater matrix, pump OK,Duo valve OK, new thermostat, etc, tried the unblocking solution, no difference, the local garage said it would cost more to replace the matrix than car than it is worth, so do I do it myself? seems a massive job, can anyone advise the procedure, or do I set fire to it and claim the insurance.
Hurry before hypothermia sets in:(

Sorry, forgot....
 

its a 1991 230e salloon

if you are referring to the heater core that will be the first blocked one that i have ever seen in a benz.last one i saw was in an early mustang 302 that had been running plain water with no antifreeze.

Then what else can it be prevents the heater blowing hot....

Firing the car to claim the insurance would never be a good idea. You could go to jail for that.

have you checked to make sure that coolant is running out of both heater hoses?disconnect hoses at firewall and adapt hose to fit compressed air and try blowing thru heater core before you attempt to remove dash and take out core.