Two thermostats on calorifier

[Tim Good]

I have two thermostats on my calorifier wired in series. One goes from 50-90 with a trip switch and the other which looks almost identical goes from 50-80.

They're both Sunvic and one is a VLK2351 and the other VKL 2301. They look like fairly standard thermostats.

The tank has an engine input and a webasto input for heating and of course the electric element.

Why are there two in series?

 

[RichardS]

Presumably these thermostats are wired so as the disconnect the electric element? Or are they something to do with the webasto controls or perhaps even operate an electic bypass valve on the engine feed, although that last one sounds a bit unusual!

Whatever, if there are two wired in series, surely it can only be a failsafe system so if one thermostat fails with the contacts closed then the second will open the contacts and shut off the heating source when the water gets up to temperature.

It's not something I've heard of before though.

Richard

 

[VicS]

I have two thermostats on my calorifier wired in series. One goes from 50-90 with a trip switch and the other which looks almost identical goes from 50-80.

They're both Sunvic and one is a VLK2351 and the other VKL 2301. They look like fairly standard thermostats.

The tank has an engine input and a webasto input for heating and of course the electric element.

Why are there two in series?

I read that as a manual reset, rather than a manual trip, on the VKL2351.

If they were wired in parallel ....deleted as rubbish.

In series ... no idea! ... Instructions for th calorifier no help ?

 

[VicS]

Further investigation suggests that it is an manually resettable over temperature limiter. For a safety critical application

 

[Alpha22]

It's normal apparently, I used to have a boat like that.... it's a safety thing..... I forget the exact logic..... but an electrician friend confirmed that it was common practice.....

 

[David2452]

Modern immersions have the overheat and thermostat in one unit but earlier ones had separates, that is what you probably have. The modern ones are to make sure that you can't omit the overheat trip, which people used to do.

 

[Tim Good]

Thanks for this.

Ok so as David said, it must be for a thermostat and overheat... although it seems that a previous owner replaced one with a modern one with overheat and thermostat.... so it currently works as a triple protection.

Thanks All.