Electric Immersion Heater Problem / Potential Solution?

emsee1 · 16 Jul 2007

Hi all,

Recently, my electric (economy 7) water boiler stopped heating up the water.

The cylinder contains 1 x primary immersion heater (at the bottom) and 1 x secondary immersion heater (at the top). Using a multimeter I ascertained that the power to the primary IH was not present. As a quick fix, I swapped around the cables to the primary and secondary immersion heaters (from the isolation switches) which means the bottom immersion is functioning and the water is now warm (but not hot).

I have checked all fuses etc. and cannot understand why there is no power running to one of isolation switches.

Could I run both of the immersion heaters from the one functional isolation switch, or would the load be too great?

If this isn't possible, does anyone have any suggestions how I can rectify the fault?

Thanks in advance,

Matt

Softus · 16 Jul 2007

emsee1 said:
I have checked all fuses etc. and cannot understand why there is no power running to one of isolation switches.

I don't understand why you can't understand it. You have a fault somewhere.

Could I run both of the immersion heaters from the one functional isolation switch, or would the load be too great?

That depends on the switch, but it's statistically likely to be a 20A DP isolator, which isn't man enough for two 3kW elements.

If this isn't possible, does anyone have any suggestions how I can rectify the fault?

Rectifying is easy. Finding it is the hard bit. The basic principle is to test at various points to see which component is faulty. If you don't have enough test equipment to work on an unenergised circuit, then you'll be taking a risk.

Check first that the circuit protective device (e.g. MCB, fuse) hasn't tripped or blown. After that, with the circuit isolated, check behind the switch for loose terminations. Then check that the switch is operating - they can fuse in an open circuit state.

emsee1 · 16 Jul 2007

Thanks for a quick response.

Could I replace the isolation switch with a higher rated one, or am I risking the load on the cable?

I've already checked the MCB and the separate fusebox and there don't appear to be any blown fuses. Perhaps I could try a new isolation switch on the faulty circuit as a first step...

Softus · 16 Jul 2007

emsee1 said:
Could I replace the isolation switch with a higher rated one, or am I risking the load on the cable?

Good observation! The cable is very unlikely to be sized to carry 26A. If the MCB/fuse is correctly rated for the cable then there's no risk, but it would be wise to check.

I've already checked the MCB and the separate fusebox and there don't appear to be any blown fuses. Perhaps I could try a new isolation switch on the faulty circuit as a first step...

Remove the switch and test both poles for continuity. Furthermore, if the resistance is negligible then the switch isn't faulty.

emsee1 · 16 Jul 2007

Yes I have a multimeter. I'll test both poles...

So, if the MCB is 32A and the fuse is rated @ at least 26A I would be safe to install a 30A isolation switch to run both immersions ??

Or am I missing the point...?

Softus · 16 Jul 2007

emsee1 said:
So, if the MCB is 32A and the fuse is rated @ at least 26A

Er, there shouldn't be both a fuse and an MCB.

Which one do you have and what is it's rating?

I would be safe to install a 30A isolation switch to run both immersions ?

Getting back to the original problem - why would you want to run both elements at the same time?

Spark123 · 16 Jul 2007

I take it that its the E7 side that is playing up? When you checked for power did you do this at the correct time i.e. when E7 is on?
To answer the 2nd question re running them both from 1 supply, I doubt it.

emsee1 · 16 Jul 2007

I have a 32A MCB in the consumer unit, the cable then appears to run into a separate fusebox with two 'old-style' breakers (not sure what the rating is - assume 13A each).

I think that the separate fusebox is something to do with the economy 7 - there isn't a timer in the system (not a visible one anyway) so I assume this fusebox tells the immersion heaters when to power up (off peak).

Getting back to the original problem - why would you want to run both elements at the same time?

Errrm ! Do I misunderstand the way immersions work? What's the secondary element for???

JohnD · 16 Jul 2007

emsee1 said:
I have a 32A MCB in the consumer unit, the cable then appears to run into a separate fusebox with two 'old-style' breakers (not sure what the rating is - assume 13A each).

I think that the separate fusebox is something to do with the economy 7 - there isn't a timer in the system (not a visible one anyway) so I assume this fusebox tells the immersion heaters when to power up (off peak).

We'd love some pictures

emsee1 · 16 Jul 2007

I take it that its the E7 side that is playing up? When you checked for power did you do this at the correct time i.e. when E7 is on?

Hi - There is a boost function which I switched on when testing the circuit

emsee1 · 16 Jul 2007

We'd love some pictures

Why am I getting worried ?

dannyboi2003 · 16 Jul 2007

The immersion heater configuration you have works as follows:

Your top element is connected to your 24/7 supply and you switch it on/off as required to top up the hot water, for example when two people want a bath and you need to reheat the water quickly for the second person. This is typically connected to your house consumer unit protected by a 16amp mcb, with 2.5mm cable to the isolation switch which will either be a 20amp dp switch or a 13amp fused spur.

The lower element is connected to your E7 supply and is only live during the night when the E7 timer kicks in. This will heat your water overnight on the cheaper E7 rate giving you nice hot water throughout the day. This is typically connected to your E7 consumer unit protected by a 16amp mcb, with 2.5mm cable to the isolation switch which will either be a 20amp dp switch or a 13amp fused spur. This circuit will only be live during the night which is why you may not be seeing the circuit as live when you test it.

We already know the element isnt faulty as you have swapped it over to the 24/7 supply. Things to check would be the fuses/mcb's at the consumer unit (which i gather you have already done), next step would be to check if there is power at the switch at night when the E7 is live, next change the fuse if its a fused spur switch, finally change the switch completely.

Let us know how you get on, if none of the above advice works then you may need to call an electrician who will have better test equipment to locate the fault.

All the best
Dan

emsee1 · 16 Jul 2007

Hi Dan,

Many thanks for that. I'll take your advice and then failing that, get an expert in...

Thanks,

Matt

ColJack · 16 Jul 2007

post us a picture of your fuse boards and metering arrangement and we'll be able toidentify things a bit more clearly and offer advice accordingly

Chri5 · 16 Jul 2007

Where E7 isn't required these do the job via MK

One radial feed and manual switch, best run through a timer to avoid getting up an hour before bath / shower

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Electric Immersion Heater Problem / Potential Solution?

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