[LLN]

I have 3-1000w convector baseboard heaters wired in parallel, total 3000w 240 volt. There is a programmable thermostat for these three. Load allowance for thermostat-4000w. All heaters are heating. The thermostat and the 1st basebrd heater are new, this was done to try and resolve the problem. No resolution. The problem: the thermostat program is set for 19.5c the heaters are on. The thermostat will not go above 18.4, thus the heaters remain on. If I program thermostat to 18c the heaters do shut off.
What I have tried: capping the two black thermostat wires and throwing the breaker on to see if breaker shuts down. It doesn't. Tried an old rotary thermostat, but couldn't see if the set temp. was being reached. Taken all the covers off the heaters and checked that all connections were good. They are. The one thing I haven't tried (because I don't have the tool) is checking the voltage of the breaker, thermostat and the baseboard heaters. Talked to an electrician who said it was the really cold weather and to wait for milder temps. Well today is mild and thermostat is no different... comments, suggestions please.

[smoothy]

Might be a defective thermostat... even if it is new.