Hi. I have an emersion heater/boiler for my main hot water system. One heating element at the bottom and one half way. The (economy 7) element at the bottom is not working, but I am not sure if it is blown or not. It’s only been in for a year which seems a bit quick to blow as it was a good quality one. So have tested it the last two nights. First night: The switch goes on, light comes on, and I can hear the element working. Then when I woke up the fuse had tripped on my fusebox. Second night: same again but the fuse did not trip. But no heated water. I am wondering if this is a case of a thermostat to be changed, but weird that the fuse flipped… Obviously I am hoping to avoid draining the tank and replacing the element, at either great expense or great hardship to me! Any advice? Thanks, Mike.

Hi Mike and welcome, with the power off, disconnect the wires from the element and read resistance with a volt/ohm meter. Do you own one and know how to use it?

Hi, thanks for replying. I don't own a volt meter but can buy one. No idea what I should touch with red and which with black. I guess if I try both. What should I expect it to read? Does that just tell me if current is passing through it? Just ordered one of these, I should own one anyway. Compact Digital Multitester With Diode And Hfe Test: Amazon.co.uk: DIY & Tools Mike

Hi Mike,

To check the element, turn off the breaker to water heater. For safety yo don't want any current at the water heater and you don't want any current going through the meter. The meter battery will provide the necessary current to do a continuity check.
Remove one of the wires from the element. This will insure that the current only has one path. That is through the element.

Set your meter up as shown in the picture below. In the picture, the meter is being used to check a resistor. You will be doing the same thing for your element.

Turn the dial to continuity/resistance. The symbol for resistance is the Omega (little horse shoe).

Note that the screen will show 1. to the far left. That means that the meter is working and that there is infinite resistance. In other words there is no connection between the leads. Touch the leads to the element terminals. What reading you get will depend on the wattage of th element. Any reading other than the 1. to the far left means that there is continuity through the element. In other words the element is good.

With all that said, a defective element would not cause a tripped breaker. By tripped breaker (you said fuse) I assume you mean the breaker in your electric panel and not the over temperature sensor in the upper thermostat.

Where are you located? I suspect UK or EU. In US we would not use the term emersion heater/boiler. We would just say electric water heater unless we were referring to some kind of combination heating/ domestic hot water system. Nor is it common to have a night setting on a water heater.
I suspect a problem other than a defective element.

Yes, it's an electric water heater that does the hot water for my whole apartment, so it is a word of domestic system, but doesn't do heating also.

OK, well I know what to do now to test it once my meter arrives so thanks very much. I was told that the breaker (yes, you assume correctly when I said 'fuse') trips with a corroded element (we have very very hard water in London) which is effectively in contact with the water, which is why it trips when it comes on. We have this nighttime cheaper electricity here that comes on at night for 7 hours. Economy 7.

I wonder what to do next is the element seems OK...

Thanks, Mike

Do a continuity check between each element terminal and the tank to see if indeed the element shell has corroded enough to create an electrical path between the actual heating element and the water.

Quote:

---

We have this nighttime cheaper electricity here that comes on at night for 7 hours. Economy 7.

---

I assume that means you get a cheaper rate during evening hours. No settings, switches or timers on water heater. Just a plain old two element water heater.

Hi there, so my meter arrived and I just tested it all. I tested both elements and both thermostats. Both gave readings other than 1 on the left. The only difference being that on all but the element which is not working (for whatever reason) the numbers on the meter counted down to 0.00 very quickly. On the element that isn't working the numbers counted down to 0.00 from about 25.0 but counted down very slowly. Almost a minute. That is all I can tell that was different. Not sure it means anything though.. Thanks, Mike

Hi again Mike, How did you determine that the bottom element was not working? Did you get a reading from the water heater housing to each of the element terminals as Harold requested?

I only determined that the element wasn't working because I am not getting any hot water. Nothing more scientific than that. I just tested touching each terminal on the element, touching the other end of the meter to the top pipe going into the tank (the tank is totally sealed in insulation. Each time I get a reading

What you are doing is checking continuity and checking the amount of resistance in the conductor or material in the element.

As stated earlier the 1 to the far left indicated infinite resistance, meaning no complete circuit, element has burned into.

Every thing has resistance. Some materials (conductors) has more resistance than others. The higher the resistance the more heat is created as a given amount of electricity (amperage) is passed through it. A material with low resistance will create only a small amount of heat. That's why we use copper for wiring. It has a relatively low resistance.

A 240 volt, 4500 watt element will use or pass 18.75 amps.
Power (in watts) divided by voltage equals amperage.
P/V=A
4500/240=18.75

Resistance (in ohms) is equal to voltage divided by amperage.
V/I=R
18.75/240=12.8 ohms

A 4500 watt element should show approx 12.8 ohms.

In order to measure very low and very high resistance values there are several scales settings on the meter. Meter should be set to the lowest scale which is probably 200. Highest is probably 200K or 200 thousand or even 2 million.

If meter is set to a higher scale, 12.8 ohms would be to small to show up on read out.

If meter is set to 200 scale and shows 0 or no resistance, that would mean that something has happened to the element such that there is a direct connection between the element terminals. As you noted earlier corrosion may have affected the element.

At least one of the wires to the element should be disconnected to ensure that there is no electrical path between the terminals other than through the element itself.

If meter is set to 200 and one wire is disconnected from the element, I would say that you have a defective element. With no resistance, there would be no heat generated. Resistance is also what limits the amount of amperage that passes through the element. With no resistance, no limit on amperage and the breaker would trip.

With a analog meter the needle responds almost immediately, with digital meters it does take a few seconds to display the reading.

Since you got 0 reading on the upper element, if I understand correctly, I think something is wrong with the way you took the readings.

May I ask why you said earlier that replacing the lower element would involve either great expense or great time and labor to you. Elements are not very expensive here and changing only involves draining the tank, unscrewing the old and screwing in the new. Biggest hassle is usually draining the tank if there is a build up of sediment in the bottom which blocks the drain valve. This comes from not periodically flushing the tank to clear the sediment.

Just saw your latest post. You touch the meter leads to the element terminals. One to each terminal. Of course with the power off and one wire removed from the element.
A 0 reading between an element terminal and a pipe (which is connected to the tank) would indicate a short circuit between the element and the tank.
Can you post a picture of your water heater?

Thank you! Tested and top element showing a number and bottom one stuck on 1. So ordered a new element and all the tools required to change it myself. Thanks so much for your help! Really kind of you to take the time. Mike