when the water runs hot all of a sudden it starts cooling down and shows either E 33 or E 34 code then it clears and runs hot again this keeps happening on and off while the tap is running i looked at the pressure gauge and the marker is on the 2nd blue dot under the black ones if that makes any sense

scruff, September 2010

the heatexanger is blocked , therfore there is not enough flow and the water goes above the seciruty level and the boiler shutdown untill it is cooled off

William, October 2010