Flashing lights on a dimplex storage heater?

My son has just bought a house and two of the storage heaters are giving us problems. I cannot see any identification at all except for the manufacturer (Dimplex).

At top right (toward the back) there is a sliding thermostat (not a knob) and below that a row of an on/off button, what seems like a power indicator and finally a light which appears to come on when the thermostat is below Room Temp ( on the units that work).

On those which are not working, at low thermostat settings both lights are on. As the setting is raised, the power light goes off and the "on" light starts flashing.

Any help would be greatly appreciated, Thank you

John Dyhouse
September 2015