Our boiler works intermittently. Some mornings the heating comes on at the right time 6.15-7.15 am and the radiators get hot, sometimes the heating comes on (we can hear the water going round the radiators) but the radiators become tepid at best. The same is true of the hot water some mornings it is hot after a few seconds and stays hot long enough to use it. Sometimes it runs hot straight away but only for a few seconds then runs cold. External temperature doesn't consistently make a difference and the boiler repair man was unable to find a fault. Before he came out a week ago he asked me to put the radiators on for half an hour before he arrived and that day they worked well. Since then sometimes they work and sometimes they don't. Has anyone else experienced similar?