Echo plus 1/4 hp chiller

[lngrhaul]

I've had my chiller for a few years and it has always done a terrific job of keeping my tank steady at 77-79.

On the weekend I noticed some strange things in my tank and when I put my hand in the water it was freezing! I checked the chiller and it said the water temp was 80 and I double checked the settings and they were still at 77-79.

I put a couple of thermometers in the tank and the temp was 66.5

I don't normally have a heater so I scrounged one up and brought the temp back up to normal......everything seems to be much happier.

So the question is - what would cause the chiller to misread the temp and drop the temp down that low?

Any tips are much appreciated