Problem with heatpac 90 boiler

I have a problem with my heatpac 90 boiler.I find it hard to get it to start, usually I have to keep pressing the reset and red button. When it cuts out it won't restart, if the thermostat is turned up full the boiler continues. Is this a thermostat problem or a circulation problem

When you say the reset, are you talking about the high limit reset on the temperature thermostat? When it stays on with stat turned up, does it eventually go to lock out or operate on/off as it should.