help with meaning o, vaillant boiler

[hudzhd1]

I have a vaillant boiler, when you hold the '+' and '-' buttons simultaneously, the display flashes between temperature and something else (which I can't remember), the boiler seems to run at full heat on central heating, when you release a tap, the domestic hot water also runs at full heat and is extremely hot,(I think) when the maximum temperature has been met the boiler will switch back to central heating mode. when it switches between central heating and domestic hot water, it does this very quickly. i.e. you will hear the gas valve open and the flame indicator on the display, even before the diverter valve switches positions. My question is, what is program for and what does it mean. When I press the '+' and '-' buttons again simultaneously, the boiler will go back to the normal mode.
thank you for your helpful advice

 

[twgas]

If it is working in normal mode - LEAVE THE F****R ALONE.

 

[mrgas]

Its an engineers mode for doing a variety of tests.
You would be well advised to leave that well alone.
Is your boiler working ok?

 

[linkyplumb]

As already stated this a service function mode, to enable boiler to run at full rate so that engineers can carry out tests that they need to.
Also advise to leave well alone.

Graham

 

[hudzhd1]

Oh, thank you everyone, the boiler does work fine 'mrgas', I were just curious thats all, but again, thanks