Immersion heater element and stat

[seasickstevie]

Puzzled why your old-style immersion heater has a standard small thermostat with just two live only (in/out) terminals, whilst I now seem to often come across the much larger live & neutral (often double pole cut-out I believe) Cotherm type.

If I ask the supplier, you invariably get conflicting sales-pitch-speak.

Wonder what anyone with an unbiased opinion would say.

Looking to replace an 11" element in unvented cylinder.

 

[Taylortwocities]

The Cotherm device is an all in one item that is commonly found in unvented cylinders (MegaFlo, etc)

Its like that so its a single unit and easier for electrically unskilled people to connect up (eg plumbers). It connects to the tank element through spade connectors.
So its an easy, but expensive, swop. It gives Cotherm an excuse to charge £80+ any time the stat goes wrong.

Not sure about the "double pole" tag. There's two contacts inside: the stat and the over temperature trip. They are (I think) both in the live connection wiring.

 

[seasickstevie]

Thanks ttc.
Looking at the Cotherm, it's shown (I think) by the dotted line through both poles. I'm guessing that that's the over temperature device.
Not sure if there's a regulation that states over temperature has to operate both poles.

 

[Taylortwocities]

Not sure if there's a regulation that states over temperature has to operate both poles.

There isn't. On a standard immersion the stat and the over temp device are in series. If there a reg, then that would not meet it.

HOWEVER, the Cotherm TSE, etc has a 1 pole thermostat and 2-pole safety limiter.
https://www.cotherm.com/wp-content/uploads/2015/11/TSE_TSR.pdf