Emersion Heater Thermostat

[chriswood]

We are talking about a normal sized domestic installation  here not a factory I think.

Yes but to solve a problem I had with a thermostat I just used an Octal plug in relay mounted in a small project box and solved my problems with contact burn out in a thermostat.
2 to 3kw heaters place a fair old load on the contacts of the thermostat and a small box on the wall  in the airing cupboard is unlikely to be a problem.

Chris

[Nick]

As I mentioned in Post #2, it's better to use a cheap zero-crossing SSR than a relay.

Regarding other posts here - modern tank thermostats (I assume this is a modern tank!) are not directly in contact with the water - they fit in a thin tube which projects into the tank - the thermostat is dry - it's the contacts that fail due to overload and arcing (switching an inductive load) - an SSR removes all that.

[ppppenguin]

The heater is a heavy load and possibly with high inrush current due to low-ish cold resistance but is it really inductive? In any case Nick's suggestion of a SSR solves the problem, and without the "clunk" of a relay that's tough enough for the job. It also solves the problem of the overheat emergency stat as I think the 2 sets of contacts are in series in the stat.

[Radio Fixer]

Lots of good stuff here and again thanks to all.

I fancy the SSR as the best solution, it would be good to come across one that is all ready boxed up ...

Will start looking as soon as I get fired up.

Gary

[ppppenguin]

Whether you use an SSR or mechanical relay you'll need a supply for the control side. Unless this is also mains voltage, then a capacitor dropper, rectifier and zener is a simple answer.