Immersion Meltdown

[Gee]

A mate called me to say that he has no hot water due to the immersion heater not working. He also tells me that there is sings of melting in the consumer unit. Am I right in saying that he needs a new thermostat fitted. Advice most appreciated.

 

[ban-all-sheds]

Signs of melting in the CU is extremely bad news. He does not need a new thermostat - if that was on the blink then all ( ) that would happen would be the hot water tank boiling.

If the immersion heater has failed, and this has resulted in such overheating of the circuit that the CU shows signs of melting then as a matter of umost urgency that CU needs inspecting, as does the cable supplying the immersion heater.

He may need a new CU and a partial rewire.

If the CU is badly damaged, he may be at risk right now of the trouble spreading.

 

[kai]

The Earthing to the immersion may be suspect, as the mcb did not trip out in such a serious fault.

A run of 10.0.sq.mm. (TEN-mm) cable from the Immersion Cylinder to the Mains earthing terminal can be a good idea...

 

[Gee]

The Earthing to the immersion may be suspect, as the mcb did not trip out in such a serious fault.

A run of 10.0.sq.mm. (TEN-mm) cable from the Immersion Cylinder to the Mains earthing terminal can be a good idea...

OK, I have just come back from looking at the CU and a wee chat with mate. The CU at the immersion mcb area does show signs of overheating but not quite melting. He tells me after tripping the mcb manually then switching it on again no more power went to the heater. I can't quite figure out the problem here! If the heating element was on the blink would this cause the overload. No power now to the element. Does this mean element packed in and or mcb packed in? I don't know.

 

[breezer]

it is possible that the element "shorted" taking the mcb with it (i am not saying that is what did happen)

 

[securespark]

all ( ) that would happen would be the hot water tank boiling.

Ban: On Friday, I visited a house where the stat failed on an imm htr, and the tank failed - boiling hot water everywhere - enough to melt candles in the next room into nothing!

Amazingly, an H92 powerbreaker spur adjacent to the tank survived, and is happily supplying power to a shower pump once reset!!

 

[ban-all-sheds]

The CU at the immersion mcb area does show signs of overheating but not quite melting.

What are signs of overheating but not quite melting?
If the CU, or adjacent MCBs are damaged, then inspect/test/replace is called for.

PS - don't listen to Kai and his mad earthing ideas.

 

[ban-all-sheds]

On Friday, I visited a house where the stat failed on an imm htr, and the tank failed - boiling hot water everywhere - enough to melt candles in the next room into nothing!

Aren't they supposed to be vented? Mine was, until I went combi.

 

[AdamW]

New stats (dunno since when) fail to an isolated state, that is if it goes, the element switches off and you get cold water, not boiling. Great idea, provided you can get a new stat quickly!


My immersion failed a couple of weeks ago, didn't really cause any problem (apart from the cold power shower I endured one morning). The live element was exposed to the water in the cylinder. This is slightly conductive due to the salty deposits in the cylinder. Current flowed to earth (the cylinder) via the water.

I got some lovely bubbling sounds as it turned my water into oxygen and hydrogen, but due to the high resistance of the water, the fuse (not MCB/RCBO) was fine. Certainly glad the cylinder didn't fail That is surely a rare occurence, as ban says they are vented, and I wouldn't think copper is that soft that boiling water would split it.

 

[kai]

That is why you should apply regulation 607, and earth the cylinder too properly, or you may receive a fatal shock if this happend in your home.

10.0.sq.mm. earth is NOT OTT in this instance, it reduces the touch voltage to a lower level, in the event the fuse fails to blow.

You might note that I have a tenby clamp on ALL pipes leading to and from the cylinder, linked with 10.0.sq.mm. earth cable back to the fuse box.

 

[ban-all-sheds]

That is why you should apply regulation 607, and earth the cylinder too properly, or you may receive a fatal shock if this happend in your home.

10.0.sq.mm. earth is NOT OTT in this instance, it reduces the touch voltage to a lower level, in the event the fuse fails to blow.

No it won't. If the circuit has been properly designed, and the earth-fault loop value is within what it should be, then there is no need to stick a 10mm² parallel earth path in there. If your R1 + R2 value is too high then you need to look at the whole thing, not just bung in a thick earth cable.

Read the quote above - but due to the high resistance of the water, the fuse (not MCB/RCBO) was fine. That high resistance would have kept the touch voltage of the cylinder low, and I'd be very surprised if the fault current would have been raised to the point where it would have blown the fuse just by the presence of a 10mm² parallel cpc...

You might note that I have a tenby clamp on ALL pipes leading to and from the cylinder, linked with 10.0.sq.mm. earth cable back to the fuse box.

Hard to miss....

 

[kai]

High Protective Conductor Current Equipment.

Reg 607 does mention Duplicate Earth Conductors, or a minimum single one of 10.0.sq.mm. to be installed. See the IEE onsite guide accordingly.

 

[ban-all-sheds]

Heaven help us.

That reg was not written with faulty immersion heaters in mind!