why is there an additional contact thermostat on my water heater ?

[Brann-]

Hi,
On my Sigmar water heater (model BO 60) there are two small wires marked "contact thermostat, max 4A, closes at 65°C open at 45°C" on top of the main electrical AC connection and its three wires.

It seems this has nothing to do with the thermostat of the electrical resistance (which needs way more than 4A btw), so I don't have a clue what I should do with it, if anything (and no, there's nothing in the manual)

thanks a lot
Cheers,
Brann

[a64pilot]

Is it connected to anything electrically?
I can only think it is some kind of overheat sensor, maybe some kind of alarm?
That is purely a guess

[Brann-]

No, it's not connected to anything. There are two wires that seemed to be connected to the sensor, so my guess is that I can use them to power a relay (or a LED, or a buzzer, or anything else) if the temperature is above 65°, but I have no idea why I would do that ; maybe just an indicator that the water inside the tank as reached a proper temperature ? It's the first time I see anything like it ...

[a64pilot]

Assuming it’s in contact with the tank to measure water temp, I think your correct.
Doubt its an alarm in that case, cause 65c isn’t alarming hot I don’t think.

[Luckyknot]

That is actually pretty hot for a water heater. 49 C would be normal. In certain situations 60 C is good for legionella and such. 65 C would be a good alarm point I would think. Where I work (hospital setting) we keep instant water heaters at about 49 C and any tank water heaters at 60 C. I think 65 C would definitely indicate there was an issue before it became serious. That would be a pretty big overshoot of the typical 60 C limit. I don't know your systems though so this is just food for thought. Hopefully somebody here with your exact unit can be more helpful.

[MAC-A-TAC]

Should be wired in series with the lower temp stat. It is intended to stop a dangerous overheating situation. It is a safety feature that should not be disconnected. Testing at normal temperature it should be closed and have continuity if tested with a meter. If it is open it may have been bypassed to get hot water. If the low temp stat fails the way it is you could experience some nasty burns.

[stormalong]

The 4 amp rating makes me question it's purpose. Are you on 120 or 240 volt power. At 240 4 amps is less than a kilowatt. How big is the heating element? Usually these thermostats are rated much high than the actual load. As MAC-A-TAC said it may have been bypassed due to failure.

[jhulmer]

Originally Posted by MAC-A-TAC

Should be wired in series with the lower temp stat. It is intended to stop a dangerous overheating situation. It is a safety feature that should not be disconnected. Testing at normal temperature it should be closed and have continuity if tested with a meter. If it is open it may have been bypassed to get hot water. If the low temp stat fails the way it is you could experience some nasty burns.

I second this answer. This is the way my previous boat water heater was wired. 4amps because it is only switching the thermostat.

[stormalong]

Originally Posted by jhulmer

I second this answer. This is the way my previous boat water heater was wired. 4amps because it is only switching the thermostat.

Thermostats are not relays. What do you mean it was switching the thermostat?

[jhulmer]

Originally Posted by stormalong

Thermostats are not relays. What do you mean it was switching the thermostat?

You are correct, poorly worded. I meant that the Thermostats (one high temp and one low temp) operated a contactor that turn the heating element on and off.

[a64pilot]

Originally Posted by jhulmer

You are correct, poorly worded. I meant that the Thermostats (one high temp and one low temp) operated a contactor that turn the heating element on and off.

That is often called as relay, and most water heaters are not that complex.

[jhulmer]

Originally Posted by a64pilot

That is often called as relay, and most water heaters are not that complex.

yes that was an old boat with an old water heater. In my current boat I just installed a new isotherm water heater I think it just has a standard household water heater thermostat with adjustable temperature.

btw- and off topic but a good foot note. I have plumbed a 12v solenoid valve and thermostat inline with the engine cooling heat exchanger to control the temperature when running the engine. before It would get so hot that it would activate the popoff valve.

Brann-
can you post some pictures? that would help us a lot to answer your question.

[stormalong]

Originally Posted by jhulmer

You are correct, poorly worded. I meant that the Thermostats (one high temp and one low temp) operated a contactor that turn the heating element on and off.

I have never seen a water heater that used a contactor, ie, a high current relay to power the heating element. What brand of water heater did that?

[jhulmer]

Originally Posted by stormalong

I have never seen a water heater that used a contactor, ie, a high current relay to power the heating element. What brand of water heater did that?

I don't recall the brand it was some time ago. It had a thermostat high on the tank and a thermostat low on the tank (screwed to the outside of the metal tank. They were wired to an enclosed switch that you wired to 120v. when you turned it on you could hear a click. The element was wired to the output.

It is obviously an obsolete way of controlling the temperature now.

I'm sorry I mentioned it now, because when I looked up the OPs water heater it is a modern unit and he is right the wiring instructions and illustrations don't show nor mention any kind of extra connection.

[a64pilot]

Quite a few house units have twin heating elements and dual thermostats, one above the other. The thermostat controls the current directly, I have never seen a relay employed, which doesn’t mean there aren’t any.