Storage Heater Elements. How long do they last ? Any Electricians...

[Mooly]

If you look at the picture, would you believe the element that has failed is the one on the left.
That twisted burnt element at the right still functions unbelieveably and reads just under 70 ohms approx which is about correct.

We have four storage heaters, and this one has had an element fail for the second time... and that mangled thing... well that makes it three failures. The heater is only around 5 years old... first failure after just 15 months or so. The other 3 are Dimplex, this one is Alto brand but is identical internally to the Dimplex.
Before I pulled it apart I decided to replace all 4 elements... good job too looking at this.

So question... how long do these things normally last ? The oldest Dimplex with these 850 watt elements is over 12 years old and going strong. The heater doesn't overheat... they just seem to fail for some reason.

[star882]

It looks like the heater uses analog controls, which put the elements through a lot of thermal stress cycles.

Maybe it's possible to retrofit it to digital control, using a SSR to switch power. The SSR can be cycled very quickly (one cycle on, one cycle off for 50% power) or even phase angle controlled. The microcontroller can be programmed to ramp the power up and down to minimize thermal stress.

If only 50% heat output is needed most of the time, a very simple solution is to add a rectifier in series, bypassing it only if full heat output is needed. In fact, that trick is frequently used in appliances. I read a story about how someone kept having to replace the elements in his water heater because of hard water. He installed a rectifier (of proper ratings in a proper enclosure) in series with the water heater and he never had to replace another element.

[infinia]

Hi
How does it fail.
My experience with elec stoves is the connector or socket goes first mostly,,, maybe should repace both element and socket as a pair. ie Once one side conn is damaged it causes the other side to go sooner than later.
The connector system really takes a beating with movement from thermal cycling.

[Mooly]

Originally Posted by star882

It looks like the heater uses analog controls, which put the elements through a lot of thermal stress cycles.

Maybe it's possible to retrofit it to digital control, using a SSR to switch power. The SSR can be cycled very quickly (one cycle on, one cycle off for 50% power) or even phase angle controlled. The microcontroller can be programmed to ramp the power up and down to minimize thermal stress.

If only 50% heat output is needed most of the time, a very simple solution is to add a rectifier in series, bypassing it only if full heat output is needed. In fact, that trick is frequently used in appliances. I read a story about how someone kept having to replace the elements in his water heater because of hard water. He installed a rectifier (of proper ratings in a proper enclosure) in series with the water heater and he never had to replace another element.

Interesting idea using SSR. Yes these are very much analog Actually this heater uses a hydrostatic stat that has a capillary tube on top of the core case.
The old thermostats (bimetal) cycle on/off pretty quickly I notice, and these don't... perhaps being off for 40 minutes then on for 20 or 30
Wondered whether the calibration is out.

I agree, solid state control would be excellent.

[Mooly]

Originally Posted by infinia

Hi
How does it fail.
My experience with elec stoves is the connector or socket goes first mostly,,, maybe should repace both element and socket as a pair. ie Once one side conn is damaged it causes the other side to go sooner than later.
The connector system really takes a beating with movement from thermal cycling.

It just fails by noticing that it's either cooler at one side, or by noticing the side away from the sensor is red hot (as the sensor side doesn't reach it's temp fully to cut off the stat).
However all the elements have definite signs of overheating... the metal dissintegrating. There was a pile of fine dust (metal) at the base of each.
The connectors fortunately are extremely high quality and obviously designed for the heat stress involved... they all appear as new still.