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Discuss Hot Water cylinder and 2x immersion heaters in the Electrical Forum area at ElectriciansForums.net

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Apprentice electrician (coming towards the end of my 1st year) here and looking for some help and understanding.

I have moved into my flat and I have both a normal CU running 24/7 and an off peak CU.

The flat has no gas and all electric. I have a hot water cylinder which has 2 immersion heaters in it. One near the top and one near the bottom. I am guessing the bottom one is the economy one which only comes on at night and the top one is for when I hit the boost button?

The controller is in the kitchen which is a horstmann economy 7 quartz. This then goes to a single FCU which has 2x 1.5mm flex's in it, one for the top and one for the bottom heater. FCU is fed by a 2.5mm cable.

The 13amp fuse is has blown. I tried changing it and it blew again, then the MCB, 16amp tripped also. On making sure all the connections were ok, every cable was very hot. The new cylinder was installed in November last year apparently.

Now I have no hot water what so ever.

Should the economy heater not be on its on supply from off peak CU? Am I better rewiring this? Off peak CU to off peak heaters via a 20amp double pole switch and a new supply from the 24/7 CU to a FCU, to a controller then to the top heater?

Cheers.
 

suffolkspark

Electrician's Arms
Are you sure you havnt already played with it? The 2 immersions should wire back to the horstmann seperately so they dont run together otherwise yes you will pop fuses because its trying to draw 6kw on a 13A fuse
 

MDJ

The Muppet Police
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Apprentice electrician (coming towards the end of my 1st year) here and looking for some help and understanding.

I have moved into my flat and I have both a normal CU running 24/7 and an off peak CU.

The flat has no gas and all electric. I have a hot water cylinder which has 2 immersion heaters in it. One near the top and one near the bottom. I am guessing the bottom one is the economy one which only comes on at night and the top one is for when I hit the boost button?

The controller is in the kitchen which is a horstmann economy 7 quartz. This then goes to a single FCU which has 2x 1.5mm flex's in it, one for the top and one for the bottom heater. FCU is fed by a 2.5mm cable.

The 13amp fuse is has blown. I tried changing it and it blew again, then the MCB, 16amp tripped also. On making sure all the connections were ok, every cable was very hot. The new cylinder was installed in November last year apparently.

Now I have no hot water what so ever.

Should the economy heater not be on its on supply from off peak CU? Am I better rewiring this? Off peak CU to off peak heaters via a 20amp double pole switch and a new supply from the 24/7 CU to a FCU, to a controller then to the top heater?

Cheers.
Have you meggared the element to earth to see if it is down, this is the answer 90% of the time.
 

Marvo

Admin and gender confused
Staff member
Admin
I'm not sure about your off-peak systems, I'm not in the UK. Maybe one of the members closer to you has some info on this.

Does thew tripping happen instantaneously or is it after a short period of time?

If your elements were working fine and now they're tripping / blowing fuses I'd suggest you first trace the fault. Isolate power, test for dead, disconnect both elements, visual check for leaks, IR test, continuity test elements and same again for the wiring. Sometimes faulty element tubes don't show up very well on tests and it might be necessary to drain and remove elements to properly visually check them for cracks or splits.
 
I haven't played with it cause I wasn't sure.
Are you sure you havnt already played with it? The 2 immersions should wire back to the horstmann seperately so they dont run together otherwise yes you will pop fuses because its trying to draw 6kw on a 13A fuse
No played with anything. Only thing I have touched is changing the fuse. It is a single 2.5 t+e feeding the fcu with both elements being feed from it. Also took out the 2 flex's and IR tested them.

Surely it would have blowing the second it was all installed and used by the previous owner?
Have you meggared the element to earth to see if it is down, this is the answer 90% of the time.
Took out the 2 flex's and IR tested them. Both came back with over 50mohms.
 

MDJ

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I haven't played with it cause I wasn't sure.


No played with anything. Only thing I have touched is changing the fuse. It is a single 2.5 t+e feeding the fcu with both elements being feed from it. Also took out the 2 flex's and IR tested them.

Surely it would have blowing the second it was all installed and used by the previous owner?


Took out the 2 flex's and IR tested them. Both came back with over 50mohms.
took the flexs out from the element or the timeclocks?
 

ashrow

Regular EF Member
If the bottom element is on the off peak CU then i would see if it is labelled, but generally the E7Q timer works on the normal rate tariff and timer turns the bottom element on and the boost button turns the top element on.
1 of the immersions is faulty (probably the lower one) but with out testing with the correct tester (insulation/multifunction tester) you will not know for sure.
It does seem strange that 2 flexes are connected in the same fused spur, there should be a fused spur which feeds the E7Q and then both immersions should be connected in the correct places in the E7Q so both cannot be switched on at the same time
 
took the flexs out from the element or the timeclocks?
There's only one time clock which is in the kitchen.

Both elements go back to a single FCU which is fed from the controller. I took both flex's out of the FCU which go into both elements. I IR'd them from the disconnected FCU side.
 

MDJ

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Hmm, Something doesn't sound right to me, unless I am missing something, ashrow above has posted what I was thinking so I am a little confused to be honest.
 
If the bottom element is on the off peak CU then i would see if it is labelled, but generally the E7Q timer works on the normal rate tariff and timer turns the bottom element on and the boost button turns the top element on.
1 of the immersions is faulty (probably the lower one) but with out testing with the correct tester (insulation/multifunction tester) you will not know for sure.
It does seem strange that 2 flexes are connected in the same fused spur, there should be a fused spur which feeds the E7Q and then both immersions should be connected in the correct places in the E7Q so both cannot be switched on at the same time
No sorry. Both elements are on the 24/7 supply. Neither is on the off peak supply.

It leaves the 24/7 CU via a 16amp MCB, goes to the timer, then from there goes to a FCU via a 2.5 t+e, then from there both flex's go to both element's.
 

MDJ

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well each element is 3KW which is 13 amps, so 1 16 amp breaker will trip won't it?
 
well each element is 3KW which is 13 amps, so 1 16 amp breaker will trip won't it?
I agree. But it's not done this before. Everything has worked before with no issues.

Would I not be better just rewiring the whole thing and making a better job?
 
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