A thermostat with safety test (heating water)

[aerialcastor]

Hello everybody



There is the water heater of one of my parents' tenants which no longer works.
There has been no hot water at all for three days and the juice arrives. It is therefore a priori the thermostat.

At room temperature, therefore when there is a demand for heat, the resistance between the two two terminals to which the resistance is connected is 0. The measurement was made without voltage.

Once connected, the voltage between the two poles where the resistance is connected is 220V.

I also had the good idea of ​​measuring the resistance under voltage so necessarily I burnt the multimeter.


Is that enough to say that the thermostat is ok?

Which would mean that resistance works the most? The water heater must be 9 years old. It sounds weird.

[dedeleco]

Hello everybody
There is the water heater of one of my parents' tenants which no longer works.
There has been no hot water at all for three days and the juice arrives. It is therefore a priori the thermostat.
At room temperature, therefore when there is a demand for heat, the resistance between the two two terminals to which the resistance is connected is 0. The measurement was made without voltage.
Once connected, the voltage between the two poles where the resistance is connected is 220V.
I also had the good idea of ​​measuring the resistance under voltage so necessarily I burnt the multimeter.
Is that enough to say that the thermostat is ok?
Which would mean that resistance works the most? The water heater must be 9 years old. It sounds weird.

basic electricity !!

It would be better to measure the alternating current in the resistance to know if it passes current there and how much !!

A simple means of testing is to put in series a small 220V lamp of a few watts (25W or even 40W), because it is it, of higher resistance, which will take all the voltage if the resistance of 1 to 2KW of the water heater is good, which will make it light up clearly. Else R dead.

The thermostat looks good but we can test better with the previous lamp by heating it to 70 ° C and see if it cuts the lamp.

Finally with an ohm meter, you can test the heating resistance and measure for example 22 Ohms for 10 A at 220V or 2,2KW of resistance of the water heater.
1,1KW is 44 Ohms for example.
If measured much more, she died.

By passing the current for a few seconds inside, so good it heats up a bit and after having cut the current, you feel the heat.

These ohmeters often have a fast fuse which dies inside and which it is enough to change to regenerate it With a bit of luck !!

[aerialcastor]

I did the bulb test which turned out to be interesting. I plugged a bulb into the resistance terminals and put the thermostat in a kettle
- At the min thermostat setting, the bulb lights up as long as the water is cold and then goes out when the water must be at 40 ° C to break everything.
- By increasing the setting, the correct water temperature is reached.

Provided that this test is valid because the bulb is 20W while the resistance 2000W, we can conclude that the thermostat works.

So I checked the hot water on site, it did not seem very cold. But the apartment is on the third floor I told myself that the water was here at room temperature so that the CE did not work.
But I did not look at what the thermostat setting and if it was at minimum it may be that the resistance works.

In any case, no one has touched the setting in recent years (screwed-on inspection door) and the water was warm before.
The question is does a thermostat wear out?


In short tomorrow I measure the resistance resistance, I reset the thermostat with a setting and then I wait.

[dedeleco]

The question is does a thermostat wear out?

it all depends on its quality and its nature.
30 years for the good ones at home and others a few years.
Old, with relay and bimetallic strip, the contacts deteriorate by sparks, oxidize, heat, and stick by welding.
There is also inside a spring bimetallic strip that goes haywire, sometimes going out of whack in the long run too.
The shaken thermostat can walk again for a while and break down after a few months, which makes it weary, we change it!
An electronic thermostat can also be destroyed, like electronics, but in general it does not restart (thyristor which ages hot), like mechanics.

We can put the 220V on the air resistance for a second and see if it starts to heat, without destroying it, because it takes a long time before overheating and melt without water.
So we are sure it is heating up.

[Flytox]

On my cumulus there is a device which checks the state of the anti-corrosion anode. Every 2 or 3 seconds a small green LED lights up to say that everything is fine. This system is mounted on a small electronic card ..... which could well control a relay to put in safety (cut the heating current) when the anode is puffed. (it is not very accessible and without diagram to understand the wiring but there is a box that looks like a relay). Maybe you have security like this?

[aerialcastor]

No, I don't have any of that.


I measured the resistance value: 35ohm. So it's ok and then if it was dead it should trip.

I reassembled the thermostat by changing the setting. Verdict in 2 hours.

[aerialcastor]

It works again.

So it was just the thermostat that triggered more at the right temperature.