Immersion Heater Thermostat Problem

[Graymond Lebroy]

Afternoon Ladies & Gents, I am having a repeat problem with my Grandma's Immersion Heater Thermostat. The thermostat is a 18" Tesla Dual safety variety from Screwfix. Grandma had a new cylinder and header tank fitted with immersion heater, no other source of hot water. I have replaced the thermostat on 4 occasions in as many months. I did notice that the thermostat terminal port had brown discolouration so checked for loose connections, one wire was loose so put it down to that. Since then it has stopped failed again. Can anyone suggest why this keeps occurring?

 

[Aquarius]

Is it on 24/7? Maybe just add a timing facility?

 

[SJB060685]

I'm not a certified electrician but loose connections can cause arking which can cause a larger amount of current to be pulled generating excess heat. Its most likely the cause and could of been far worse.

 

[John.g]

Afternoon Ladies & Gents, I am having a repeat problem with my Grandma's Immersion Heater Thermostat. The thermostat is a 18" Tesla Dual safety variety from Screwfix. Grandma had a new cylinder and header tank fitted with immersion heater, no other source of hot water. I have replaced the thermostat on 4 occasions in as many months. I did notice that the thermostat terminal port had brown discolouration so checked for loose connections, one wire was loose so put it down to that. Since then it has stopped failed again. Can anyone suggest why this keeps occurring?

If its a top mounted dual immersion (sink/bath) then the thermostat should only be ~ 11 ins long, also if a dual immersion someone might (although difficult) managed to wire the two elements in parallel which will very quickly burn out the stat, these should last for years even with fairly heavy use.
If it is a dual immersion ( or even if not) a photo of the immersion top might reveal something.

 

[Murdoch]

My recommendation would NOT to buy another Screwfix unit. 4 failures in 4 months isn’t good. Did Screwfix replace any of them FOC?

locate a local supplier and buy from them. Don’t go cheap and preferably buy a named product

 

[steadyon]

1. If your grandmother lives in a hard water area, then it is possible that the cylinder has accumulated enough limescale in the bottom for the scale to reach the immersion heater. This is likely to cause it to overheat.
2. Don't forget that modern thermostats have an additional overheat thermostat inside them. If this is triggered (normally around 80 to 90 degrees) they do not reset themselves, but have to be reset by pushing in a small button, sometimes almost hidden and requiring a paper clip or similar.
3. If the overheat thermostat trips and is not noticed, it will give the same effect as a broken thermostat.

 

[Ben-gee]

If it’s hard water use an incoloy one rather than copper, more expensive but last longer.

 

[John.g]

If known if these stats had failed completely or could have been reset then that will tell a lot, its unlikely that the op who replaced these himself would not have done this as unlikely that they would all have been replaced FOC.
It may need element removal, in which case a dual element immersion can save a lot of money especially for someone living alone.