microgenus cutting out

microgenus, works fine for hotwater, when switched to heating it will fire for maybe 3-5 mins from cold untill it gets to about 40*c, and cuts out.
wont cut back in again untill its dropped back down below this temp.

if thermistor leads are switched over the heating runs to full temp everything gets red hot all over. the system has just been flushed as rads had huge cold spots, but still never got very hot.

replaced thermistor as ariston were adiment that this was all it could be. so it was and problem still the same.

now apparantley all it can be is a blockage, even though rads can get red hot, the boiler was PF as well as the rads ,which have improved greatly from it. the radiators instantly warm up, as soon as boiler fires, im failing to see where a blockage is?

i was told that the thermistor senses flow aswell?? which i could understand if it was blocked and the water temp rose to 80*c is a matter of seconds but it wont go past 40*c

any ideas would be great

Dimly remember reading about this before, have you done a search Rob?

hi chris, just done a search, i believe the post your thinking of involved HW and central heating, something to do with electrodes

do you beleive the boiler or pipe work could still be blocked from my original post?