Would there be a way to test that?
If they are what supply the display with it's temp, it seems relatively correct - if the heating is on it sits around ~45 constantly, once the hot water is turned on it raises over 10-20 seconds to ~85, and then once the boiler turns off, it slowly climbs down...
I have a Vaillant EcoTec 937 Plus boiler.
A few days ago, it had blown it's 3amp fuse overnight, which I replaced. The boiler powered up fine, and happily supplied the house with CH.
However, as soon as a hot tap was turned on, it cut off the gas after a short while.
I called Vailiant for an...