My boiler has just started to loose pressure, it's not been used all over the summer months. the heating comes on the rads get quite hot, the thermostat appears to work comes on and off. But checking the pressure it falls below the recomend for use. No leaks found, and i have not bled the rads since they were put in. any idea's before i call in a service engineer, i have represured each time.

Royal, October 2010

The expansion vessel diaphragm is probably split and will need replacing.

To confirm this, when next time the heating is on check for water coming from the external overflow

Brian, Edinburgh, October 2010