If you are suffering from hot and cold water fluctuations on a heatline Monza combi boiler then check the following FIRST.
If when you turn on the hot water you can hear the boiler fire up with the fan at high speed then do the following to fix it without tools.
1: Hold Mode button for 7 seconds,
2: Use + or - to show 35 on display,
3: Press mode,
4: Use - to show 96 on display,
5: Press Mode,
6: press + or - to show 1 on display,
7: Press mode,
8: Wait 3 seconds,
9: Press mode button for 3 seconds or press the small reset button.
Now try the hot water again, if the boiler fan starts at a lower speed then your problem was corrupt Eeprom on the main PCB.
Basically the boiler is trying too hard to heat the water, the out sensor is seeing the quick rise and shutting down the heat, then it detects the fall in the return and fires the boiler back up again in a never ending cycle.
This also affects the Heating.
If you look at the display and the temperature rises quickly then the boiler shuts down and then fires up again the reset should cure it as long as the sensors, pump, diverter or heat exchanger is not the problem.
Refference: http://www.heatline.co.uk/wp-content/uploads/2013/09/Monza-24-and-28-Instructions-for-use.pdf.
The bloke I fixed this for was charged £70+vat by "the professionals" and was told he needed a new pump at £400 fitted. I fixed it for two cups of coffee and a sticky bun.!! And I told him not to pay the £70+ invoice as the monkeys did not deserve it.
Hope this helps you .
Hv.
Hiddenvision, September 2014
