I have a Potterton Profile 100e and it does not have a "reset button". It does have an Overheat Thermostat that trips out when the water becomes too hot and you can manually reset it by pushing upwards on a button - underneath and to the left of the heat Control Thermostat.
If you really want this button to drop down (no idea why you should) run the boiler with the heat control set to Max. Usually this control is set no higher than 3 or 4.
The nearest thing to a "reset" is to turn off the electrical supply, turn the heat control to zero, turn the power back on and increase the heat control till she fires up.
Is there something wrong with your boiler?
Peccavi, December 2008
