Heating stays cold - thermostat does not open
At the beginning of the heating season, the heating often stays cold even though the thermostat is open. This usually happens because the pin that closes the valve is stuck. Unscrew the thermostat at the union nut. Then the valve is open with the valve pin. Now tap the pen with small light strokes. Almost always dissolves due to the pressure in the heating circuit of the valve seat. The pen pops out. Then screw the thermostat housing back on and now you can regulate again.
