Storage heater tripping mcb

[jimmer]

I have a 3.4kW creda storage heater tripping a Type 3 16A Federal mcb. I have insulation resistance tested both the supply circuit and the heater and all is fine and also fired it up on a plug top and it runs for 20 mins fine and trips no fuses at all. Its pulling around 14 amps so i would expect the elements to be fine and there is no visable signs of damage. Its only the next morning the client rings up and says the mvb has tripped. Is it possible the mcb has gone weak? or is there something else i am missing?
Any help much appreciated, cheers

 

[Dcf]

A few years ago I got a call to a social housing complex with a similar problem.
after a few visits I tracked it down to a poor plug in connection on thr federal panel board.what a pile of cack that thing was.worth a try.failing that strip it down n visually check elements

 

[PC Electrics]

Did you check the resistance of the elements or was that 14A measured?

Assuming the machine checks out okay for continuity values and IR (along with the circuit), then suspect the mcb. Is it installed with another device either side? Many manufacturers recommend a rating factor of 0.8 if loads are continuous and there is no air either side. If so it may have become "over sensitive" with age due to heating. If the cable is 2.5 and the install method will support it, change it to 20A.