defrost heaters sumberged in water (ice) prone to fail ?

[Yuri B.]

Merry Christmas!
I am interested whether ANY evaporator defrost heater is going to fail when submeged into water for a time (then bound inside ice block upon cooling start) - as result of drain blockage leading to condensation water gathering, for example. Or are the six heaters, failed in such a manner recently in the bottom part of a Rivacold evap., an exception ?

[martinw58]

as the ends of the heaters are sealed to stop water geting in to them thay should be ok

[install monkey]

as long as the heaters were in contact with the water to reject the heat, if the water level dropped due to evaporation/ partial drain blockage then it may fail

[joe-ice]

This wouldnt be an issue with older heaters but the amount of heaters ive come across in the last 5 or 6 years with the cable burnt off at the watertight? seal is scary.Mostly in cases with ice / drain issues.

[mikeref]

as long as the heaters were in contact with the water to reject the heat, if the water level dropped due to evaporation/ partial drain blockage then it may fail

Oi Monkey. Do you mean if part of the heater was submerged, and the rest was clear? Temperature difference between heater in water/ ice and the remainder clear to reach temperature?
In that case, heater would deform and the stress point fail.

[install monkey]

the way im reading it is drain blocked on a freezer coldroom- condensate from last defrost filled drip tray , hence froze when system restarts,defrost kicks in,water doesn't escape heater submerged in water as the heater

Oi Monkey. Do you mean if part of the heater was submerged, and the rest was clear? Temperature difference between heater in water/ ice and the remainder clear to reach temperature?
In that case, heater would deform and the stress point fail.

[chilliwilly]

Shouldn't the defrost terminate stat or probe cancel the defrost if the water level dropped due to the increase in temperature?

Is it one of those flexible cord type or rigid heaters? Sometimes the expansion pressure of the ice can cause damage to the element. Especially if a block of ice forms on such a small diameter cord.

[Yuri B.]

I was there only once and have opened that side of the evaporator where heaters connection was made. The heaters are stainless pipes about 10 mm in diameter and there are 22 of them alltogether. The evaporator is full of ice at the bottm and the six lower heaters bound in the ice shown infinity resistance. I have not yet opened the other side of the evaporator and do not know wheter the heaters are 1 pipe U-form or 2 pipes connected with a wire bridge (and possibly, something wrong will turn out to be just there)

[install monkey]

http://www.rivacolduk.co.uk/content/downloads heaters could have just failed during normal operation

[Tayters]

I've seen plenty of heaters covered in ice which have been fine but it may have been the case the frost heave has damaged them but I think an outside chance at best of that.
Maybe a dodgy batch which failed then the ice formed after?

[Yuri B.]

A week ago I returned to the place.
A couple of the heaters were taken out.
They turned out to be good just the contacts in the rubber isolation had been lost.
I foreseen it, so it should have been: laid in water resistance was minimal, current maximal, but, while heat rejection of the heaters themselves was sufficient, the contacts under the rubber, whose heat conductivity is low, ovrheated and failed.
The moral: defrost heaters cannot work submerged in water.