Strange immersion heater / CU problems, help please!

[MrTM]

Hello all,

I have a strange issue with my immersion heater. Its a 'super seven' Economy 7 immersion heater, unknown age (could be anything between 1 and 30yrs old) with two horizontal entry heating elements.

The heater is controlled with three flip switches (no timers!). As far as I can tell, one switch inside the heating cupboard controls the 'boost' as this adds extra heat (and waterflow strangely) to the water. The two in my fuse cupboard control the bottom heating element; one switch allows the element to be switched on at any time, the other only gives power to the unit during the economy 7 hours.

A day or two ago the MCB tripped on the switch that controls the on demand lower heater. I turned off the switch, flicked the fuse back and then turned the switch back on. It stayed on for 5 mins or so and then tripped again. Now I can't reset the fuse regardless of whether the switch is on or off, or even with the whole CU switched off.

What's also strange is that the element still works when activated using the economy 7 switch! Having scoured all the forums for this kind of issue I have found that in most instances the element is broken and requires replacement - but how can the element be broken on one circuit/switch and not the other?

Having just had a couple of estimates for replacement from plumbers both around £115 and being skint, I'm hoping this isn't the problem! I'm also hoping the CU isn't knackered... Any help on this would be greatly appreciated.

Thanks!

 

[ColJack]

sounds like the breaker is knackered.. try it temporarily on another one of the same rating ( take out the other wire obviously )..

if it works then it's the fuse..
if not then it might be the switch or cabling .. it's a sparky job then, not a plumber..

 

[MrTM]

sounds like the breaker is knackered..

I'm beginning to think thats definately the case. I just hope is wasn't the immersion heater that caused it to fail, as then I may need a plumber after all!

 

[JohnD]

you can't rely on the appliance switch, as it might be faulty or damaged, or there might be cable damage downstream of it.

if you turn off the main switch in the CU, and the MCB still won't reset, then it is the MCB at fault. This is easier and safer than opening the CU and swapping MCBs around.

Be aware that there might be two main switches if you have an economy 7 type installation - one for the 24 hour circuits and one for the E7 circuits. If anyone has mixed them up or connected them together you may have an unsafe installation.

Photos of the CU or CUs, and the immersion heater switches and cabling, and the cables around and between the CUs, E7 timer, meter(s) and suppliers cutout may tell us more.

 

[matt1e]

sounds like the breaker is knackered..

I'm beginning to think thats definately the case. I just hope is wasn't the immersion heater that caused it to fail, as then I may need a plumber after all!

I think its more likely to be a duel element and and its knackered!
well one side of it is anyway

Matt

 

[simond]

Difficult to interpret what you have there.

But if the lower element can be switched between the off peak, and full tariff supply, then the likely scenario is that the full tariff supply is fitted with an RCD, and the off peak is not.

An immersion heater with partially compromised insulation will take out the RCD but may continue to work on a non-RCD fed circuit.

Net result is still a new immersion heater though.

 

[MrTM]

I think its more likely to be a duel element and and its knackered!

I thought that dual element heaters were installed vertically? There are two seperate horizontal elements so I assumed they would be both single element.

if you turn off the main switch in the CU, and the MCB still won't reset, then it is the MCB at fault. This is easier and safer than opening the CU and swapping MCBs around.

I have done this and I'm now convinced that at the very least the MCB is damaged.

Be aware that there might be two main switches if you have an economy 7 type installation - one for the 24 hour circuits and one for the E7 circuits. If anyone has mixed them up or connected them together you may have an unsafe installation.

There are indeed two CU's next to each other. So far no problems with the ECO 7 CU, and they look split correctly.

Photos of the CU or CUs, and the immersion heater switches and cabling, and the cables around and between the CUs, E7 timer, meter(s) and suppliers cutout may tell us more.

I can post these up tomorrow but most of the cabling is out of sight - some runs through the attic of a neighbouring flat, but no-one is ever in! The CU's are a pair of Wylex NN 614, 100 amps, 6 slot. I googled the model and nothing came up so I guess they're pretty old.

Come the light of day I'm going to turn off all power with the CU mains switches and have a look inside the caps on both elements for obvious signs of damage, then maybe take the casing off the CU and check for the same. I shall post up any interesting/humourous pictures that result!

 

[JohnD]

Wylex NN is obsolete, but nowhere near as old as some of the "old" stuff we see.

Replacements are easily available
http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_NN_Range/index.html

looking forward to your photos

 

[matt1e]

I think its more likely to be a duel element and and its knackered!

I thought that dual element heaters were installed vertically? There are two seperate horizontal elements so I assumed they would be both single element.

no you can get horizontal ones

if you turn off the main switch in the CU, and the MCB still won't reset, then it is the MCB at fault. This is easier and safer than opening the CU and swapping MCBs around.

I have done this and I'm now convinced that at the very least the MCB is damaged.

if this is indeed the case and it will not reset when the main switch is off then the mcb is knackered but bear in mind that if it has tripped due to overload then you will sometimes have to wait till it cools down before it will reset

The heater is controlled with three flip switches (no timers!). As far as I can tell, one switch inside the heating cupboard controls the 'boost' as this adds extra heat (and waterflow strangely) to the water. The two in my fuse cupboard control the bottom heating element; one switch allows the element to be switched on at any time, the other only gives power to the unit during the economy 7 hours.

if this is correct and all there is are 3 on/off switches to control the system
then:
if one of the switches in the fuse cupboard "toggles" between peak/offpeak and the other is on/off then it will be a single element

if both switches are on/off then unless you have some kind of interface/contactor also fitted it will be a duel element
reason being if both switches were switched on and connected to a single element then then the entire off peak supply will be energised due to backfeed from the peak supply via the switches (mind you that would trip the mcb too if you also have storage heaters this hasn'tbeen wired recently has it?)
best bet as already said is to post some pics as there are a few wiring options for peak/off peak control

matt

 

[DP]

Why not get the multimeter out and test the circuit?

 

[JohnD]

perhaps because he hasn't got one (yet)?

not all householders have everything

 

[MrTM]

perhaps because he hasn't got one (yet)?

LOL, spot on, I was on Amazon a couple of nights ago considering picking up a cheap one. The flat is my first place and I've been picking up tools & gizmos as I go.

(mind you that would trip the mcb too if you also have storage heaters this hasn't been wired recently has it?)

Its an old installation. There were two storage heaters in the flat originally, but one had been removed and the other was broken when I moved in and has since been disposed of.

I've set up an album with the pics: //www.diynot.com/network/MrTM/albums/

No 'smoking gun' as far as I can see. The wiring runs through next doors attic unfortunately so I can see if there is any damage between the heater and the CU.

 

[MrTM]

PS,

The numbers represent the three switches:

Switch 1, next to the heater, operates 24/7 and I believe acts as the boost / top element as the water heats faster with this activated. Strangely, this is wired into the ring main MCB.

Switch 2, operates 24/7 and I believe controls the bottom element. This is the switch that is now inoperable. Its wired to the MCB labelled 'emersion'

Switch 3, only operates during the ECO 7 period (actually as it comes on at 10.30 for seven hours instead of 12.30) and I believe operates the bottom element. I turned it on last night, the little red light lit up, and this morning I had hot water. It has its own MCB also labelled 'emersion', but in the Eco 7 cabinet.

 

[JohnD]

can you take a clearer picture of View media item 23308
it looks to me as if the G&Y might be chafed against a terminal

You need to verify for sure which MCB feeds which switch, and which switch feeds which heater.

Also verify for sure that there is nothing connected to both CUs. If Switch 2 and Switch 3 both operate the lower heater, and one is wired to the Eco 7 CU but the other is wired to the normal CU, that is WRONG and DANGEROUS.

The bottom heater must only be supplied from the ECO7 CU, and the top heater must only be supplied from the normal CU.

It is incorrect to supply an immersion heater from a socket Ring, but that is the least of your problems.

If you have checked that, even with BOTH CUs switched off, your MCB will not reset, then it is faulty. You can buy a new one for about £16 (you need a 16A one but if this is not available 15A or 20A will do). Second-hand ones are available but I will say no more.

Before doing any work inside a CU, or even taking the cover off, turn off BOTH main switches. Test for dead first thing you do when you take the cover off. Do not remove the covers on top of the main switches as these terminals will be live at all times, even when turned off.

 

[matt1e]

hi again
its true what they say about a picture painting a thousand words,so thats the duel element ruled out! they are both single elements

next question, are you absolutly sure that the switch in the airing cupboard is for the top element? you mentioned earlier about flow increasing when switched on, is this not operating a pump?

if so then the top element is now suspect and likely operated by switch 2 first check as john has mentioned that the earth wire is not shorting against the element post then if inconclusive you can try disconecting the element before reseting mcb and switching on (see pic)
if the mcb holds and the switch lights up when disconected then the element is gone

View media item 23312