Heating stays on after thermostat cuts out.

[rgracin]

Having problems with what I first thought was the wall mounted thermostat. House is like a sauner at the moment as it seems the heating stays on regardless of the temperature. I replaced the thermostat thinking it had broken, but it still seems to be doing it with the new one.

It clicks in ok, but when it's up to temperature, the thermostats clicks out, but heating continues until a little fiddles with the thermostat turns it off.

We have a gas fired boiler (less thna 12 months old).

Any suggestions?