heating not working? help

[jim8594]

ive checked the both pipes going to the heater matrix they are clear then the two parts are clear and the pipe connected to them and also the matrix is clear so what would be stopping the warmth coming out of the fans?     and if i turn them off completely then let the engine run for five then turn them on you can feel heat for about 10 seconds then it just goes cool again? 
any help appreciated

[mk2bal]

When the cars hot, grab both flow and return matrix pipes under the bonnet, they should be hot. If they are, its the flap system that controls the heat from cold to hot, which is built into the matrix housing thing behind dash. If they're cold, then its not getting to the pipes, by either blockages, knackered pump, thermostat etc.etc.

[Neo Badness]

Bit more investigation required as suggested above but I'm going to guess the thermostat is shaggulated.

[rossbarry1]

bypass valve?