Help please: Immersion heater fault.

My house uses an electric immersion heater (copper Fortic tank).
I had the temperature set so that it was exactly right for shower purposes.
I took a shower the other day, and the water seemed a little hotter than it should have been - only by a few degrees. I could have been mistaken...
Today, the heater is not heating the water at all. Actually, the water comes out tepid, but that may be residual heat from when it was working, a couple of days ago.
As the cirquit breaker in the consumer unit has not flipped, so I am assuming the fault is either the immersion heater element or the thermostat. Both were brand new in August 2010 (i.e., 17 months ago, purchased from B.E.S.). Is it usual for one of these items to fail so quickly? I only use the immersion heater about 1 hour every coupe of weeks, as I often take my shower elsewhere.
How do I determine which item has failed? I have a multi-meter available.
Many thanks...
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

As it's fairly new, there should be two thermostats, 1 The one you adjust to set the temperature, and 2 a non-adjustable one as a backup to trip off if the first one fails and the tank is getting near boiling.
The second one is not self resetting, and might have a manual reset button on it. If it has tripped, the adjustable stat has probably failed and needs replacing.
With the power completely disconnected, you need to use the meter to test continuity (resistance) of the heating element, and of the two thermostats, and see which one is open circuit.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote in

Thank you very much for the first class help. This is just what I needed to know... I can't remember seeing any sign of a second thermostat, but I will crawl into the loft later and have a closer look.
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
AL_n wrote:

The two thermostats are combined and have been mandatory for the last few years. the safety one if fitted has a reset button. Measure resistance of the element to make sure it is intact. Measure resistance across the stat which should be closed being below target temperature.
If it is open circuit, and has a reset button, press it and see if is becomes closed circuit. If so apply power and the water should heat.
Otherwise the above measurements will tell you which item is at fault
New stats can be purchased in isolation but usually a new element will come with a new stat included. If you are replacing the element, then an incaloy one will cost a little more but will last a lot longer especially if your water is at all hard.
Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Your help is much appreciated - thank you!
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

OK, I have done the tests. (And please bear in mind, I am not an electrician.)
The heater element itself has a resistance of 20.1 (I had my multimeter set on the 200 ohm setting).
Testing across the thermostat, reveals open circuit (no reading on ohm meter)
The reset button does not depress. It is almost flush with the face of the thermostat casing. I guess this means it has not popped out.
Now here's the strange thing: None of the circuit breakers in the CU have flipped. However, when I switch the immersion heater switch to "ON", my volt meter reads .03v, when I have the red prong touching the red cable and the black prong touching the black cable (coming out of the 3-core cable, at the immersion heater).
I wondered if there was a loose screw in the switch... I unscrewed the cover of the switch. All the screws on the switch are tight. Volt meter confirms 240v across the red and black, going into the switch. When switch is in the ON position, volt meter confirms 240v at the other side of the switch.
To me, this suggests that the cable rinning from the switch to the immersion heater is at fault. However, it is a really thick pice of 3- core flex. I mean, each core is about 3mm thick. It's thicker than the cable going from the CU to the switch. No-one has been up in the loft, so it has not been subject to any possible human interference.
This seems very strange to me. Is it really concievable that the cable is what's at fault here? It has worked fine for about 20 years, AFAIK.
Thanks..
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Disconnect the cable completely and check each core for continuity.
MBQ
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks... I have just done that, and now I find that there IS 240v at the heater end of the cable. I guess my meter prong was not making contact with metal, before.
So what is the prognosis now then?
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks. I just did this, and now find there IS 24v at the heater end of the cable, testing across the red and black wires at the unconnected end of the cable.
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

OK - I have done this, and now find that I DO have 240v at the heater end of the cable, (measuring across the red and black wires). I guess my MM prongs were not making contact with metal previously.
So what is the prognosis now?
Thanks,
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You need to be more patient with your newsreader.
MBQ
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

What???
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Oh, I see..
What happened was: I posted one and then realised I neded to revise, so I immediately hit the "cancel message" option in my (Xnews) reader. I received "message cancel request sent". After that, I could no longer access the message so I assumed it was successfully canceled.
I then posted version 2 of the message.
Then I relised I'd made a typo so I repeated the whole operation again (perhaps twice more).
Perhaps my messages didn't get canceled after all, since you seem to have seen them.
Apologies for the confusion.
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
AL_n wrote:

Just for future reference, while your news server may honour cancel requests from you, many servers will not honour cancel requests from outside their user base. Once the message leaves your server and is on the peers, which can take less than a second, it is very unlikely that any cancel request will work. This means that once it gets off your system, it is then propagated throughout usenet as if the cancel request had never been sent.
--
Tciao for Now!

John.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks for the clarification. I will triple-check my posts prior to sending from now on.
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

True. I now find that I only *sometimes* get a 240v reading at the disconnected end of the cable. I am going to connect my meter to the cable- ends using a chocolate block and then move the cable around to see if positioning affects it. If so, I guess that means a break in one of the wires...
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
AL_n wrote:

It's not worth faffing about. Just replace the cable. Even if you find that cutting a few inches off one end of the old one solves the problem, it'll cost you less in time and money.
--
Tciao for Now!

John.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I have just solved it!
The immersion heter switch is a double switch. The left switch is named "bath" and the right switch is named "sink".
Well, the sink side has never worked. The cable going from that switch ends in a chocolate block, heavily wrapped in insulation tape. It was like that when I bought the house, 2 years ago.
Having discovered this, I have never used the sink heater switch. When I take a shower, I switch the left switch (bath) on for an hour to warm the water. Then I switch it off.
Last time I took a shower, however, aftyer heating the water, I accidentally switched the "sink" side off, instead of the "bath" side.
What I did not know (until now), is that if the sink switch is off, it also cuts power to the main (bath) heater element.
All I needed to do was flip the sink switch back to its original position (ON) and everything is working again.
Is that normal for the sink switch to be wired so that it also cuts the power to the main bath heater??
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
AL_n wrote:

It would seem there was originally a double element immersion heater fitted, which has been replaced by a single. It should also have been re-wired properly, or replaced like for like, but this often isn't done.
If your immersion heater fails again, it's worth paying the extra for a dual element one, as you'll only be heating half a tankful when needed, which is plenty for a shower or to do the dishes. I also fit a timeswitch as standard, so there's hot water ready in the morning. Just press the boost button for anything in the evening.
--
Tciao for Now!

John.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thank you for the suggestions. I like the idea of not needing to heat the whole tank, just to just take a shower.
It's possible that my existing tank has two elements. I did take the jacket off once, and can;t remember seeing anything looking remotely like the main element, sited further up the side of the tank, so you are probably right.
Yes, the timed swith would definitely be a good investment, (assuming they are reliable), as I sometimes forget to turn the heater off.
Al
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.