Lec Fridge Freezer temperature fluctuations

Hi,

I have a 4 year old Lec TNF60188W.
For the last 2 weeks it has been behaving rather strangely with the fridge temperature going above 10degC.

I have monitored both the temperature and power consumption with smart devices so have some nice graphs over time. Temperature and humidity (absolute and relative). With the humidity you can clearly see on the graph when the fridge door is opened!

The temperature in the fridge will be fine for a few days with the graph showing the temperature staying with around 1degC either side of the set point of 4degC. A nice sawtooth of it rising and then falling as the cooling system kicks in. This marries up with the power consumption graph. On the power side you can also see it go into the defrost cycle as the heating clears the frost from the evaporator coils (a large but short spike in current). Interestingly, the defrost kicks in at a fridge low point and appears to complete before reaching the high point that would trigger cooling. Nice.

All fine and dandy until, for no apparent reason, there is a slight movement up and down around the set point 0.3degC either way for about 20mins and then the temperature rises to around 10degC at approximately 1decC per hour. Pretty much straight up but with a slight dip after an hour for about 10mins.

This is where it gets strange. The fridge temperature then fluctuates by exactly the same sawtooth pattern as when operating normally. The power consumption is also the same. It is almost as if the fridge has been switched to a set point of 9degC. However, the controls still show 4degC and the highest setting is 8degC anyway for the fridge. It then stays at this state for 24 to 36 hours and then goes back to normal, cooling the fridge back to the set point of 4degC. I also tested this at a set point of 6 and 8 with the same results. Fine for a day or so then too high for a day or so, rinse and repeat.

The evap coils look exactly the same in both normal and fault state. Minimal frost, or none of I’ve caught it just after defrost. The freezer is absolutely fine. The humidity is similar in both states too.

It may also be relevant to say that the temperature has risen before and then gone back down a few times in its life in warm and cold seasons. However, it didn’t last long enough to cause me to investigate so deeply as now.

Any ideas? Is the controller gone or going? Is it worth a repair or should I cut and run?

Thanks in advance,

Andrew.