Problem with Siemens RDJ10RF boiler control?

I have just had a new combi boiler fitted with a Siemens RDJ10RF wireless control/thermostat. Everything works ok but once the boiler has reached the set temp and switched off it takes up to 3 hrs for the thermostat to drop enough to bring the heating back on even though the house has gone cold by this time. It is situated away from any direct heat source and I have tried it in different positions. Any one else have this problem?