hi can anyone help. i have set the thermostat to over 20 but it wont go to higher than 17. radiators are on but very low, i have turned all rad thermostats up. there is no fault sign but s7 pump overrun showing and radiator sign flashing. the temp is about 29 on the display. i turned the rad dial to about half way as recommended but the dials are very flimsy so not sure they are turning. hot water seems ok. any ideas gratefully received. thanks