Socket & immersion heater

[Grant_]

Hi

Sorry this is a two parter...

We recently got a new boiler, went from a combi back to a system boiler and tank,
The installer didn't connect up the immersion heater as "nobody uses them nowadays"

Due to one of the thermostats being DOA, he got a Worcester engineer out to check it over. who said "Aye you could just stick a plug on it"

There is a double socket above the boiler which had the tumble dryer plugged into it. It was moved up 6" to accommodate the new boiler & the tumble dryer moved a couple of feet further away to accommodate the tank so the flex no longer reaches.

I was planning to just move the socket along the wall, but as the t&e is all neatly clippe dinto place and has been painted over, I wondered about either adding a 2nd socket or splitting it into two singles. As far as I can see there are 3 double sockets in the garage that all go back to the consumer unit, but appear to each be wired directly toe a 16a breaker rather than in a ring.

So not sure if splitting adding a 2nd socket or splitting it would count as a spur off a spur?

SImilarly I'm guessing either just connecting the immersion to a 3 pin plug or to a DP isolator spurred off that socket probably isn't a good idea? Both are unlikely to be used at the same time as the main reason for wanting to connect up the immersion is to use up excess solar with an iBoost or similar, but also aware that I should take into account other folk in the house who may not remember that the two shouldn't be run at the same time.

 

[AndyPRK]

The fact its running off a 16A MCB, you can do whatever you want out of those options.

As you are going to have to add something, you may as well make it a 20A DP switch. (rather than plug and socket)

myself I would also consider changing the mcb to 20A if the cable is 2.5mm and the garage is part of the house. It stands a chance of not tripping then

 

[ericmark]

The 13 amp plug has a fuse in it, the way a fuse works is the wire inside melts, so clearly at 13 amp the wire is at near melting point, this heat needs removing from the plug or it will over heat and be damaged, specially when you consider how long it takes to heat a cylinder of water, so to allow the heat to dissipate the larger the device holding the fuse is, the better, so I would say a fuse connection unit (FCU) and a 15 amp socket would be a better option.

The 15 amp plug does not have a fuse in it, so will not get as hot. Back in 1954 when my dad's house was built, using a 15 amp plug and socket for the immersion heater was standard, and it would be supplied from the main fuse box with a 15 amp fuse, and the regulations say

The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers). This can generally be achieved by:
(i) locating socket-outlets to provide reasonable sharing of the load around the ring
(ii) not supplying immersion heaters, comprehensive electric space heating or loads of a similar profile frog the ring circuit
(iii) connecting cookers, ovens and hobs with a rated power exceeding 2 kW on their own dedicated radial circuit

so clearly not recommended to supply an immersion from the ring final, I do see that where the immersion is only really for an emergency it does seem to make some sense, but in the main the area used for the tank is called the airing cupboard and is often filled with material which will stop adequate ventilation to cool the plug.

 

[Grant_]

Thanks

The heater in my tank is rated 2.5-3kw so i know its on the upper end of 13a.
The tank is a 250l and sits next to the boiler in the garage so atleast its not in a poorly ventilated cupboard

I don't think there are any spare channels left in the CU (although the labeling is a mess) but I'll probably ask the installers when the solar is goin in if they can hook up the immersion.
Then either tap a single socket off the existing double for the dryer, or stick a junction box in place of the existing double and extend it out horizontally so i can maintain the existing vertical cable run.

The 13 amp plug has a fuse in it, the way a fuse works is the wire inside melts, so clearly at 13 amp the wire is at near melting point, this heat needs removing from the plug or it will over heat and be damaged, specially when you consider how long it takes to heat a cylinder of water, so to allow the heat to dissipate the larger the device holding the fuse is, the better, so I would say a fuse connection unit (FCU) and a 15 amp socket would be a better option.

The 15 amp plug does not have a fuse in it, so will not get as hot. Back in 1954 when my dad's house was built, using a 15 amp plug and socket for the immersion heater was standard, and it would be supplied from the main fuse box with a 15 amp fuse, and the regulations say so clearly not recommended to supply an immersion from the ring final, I do see that where the immersion is only really for an emergency it does seem to make some sense, but in the main the area used for the tank is called the airing cupboard and is often filled with material which will stop adequate ventilation to cool the plug.

 

[pcaouolte]

If you are having solar installed it is possible to get a device which uses the surplus electricity from your solar panels to heat your water. This ensures that you use more of the power that you are generating and store it as heat in your hot water tank, effectively getting some free hot water. See here for information (just an example of what can be done): https://www.thegreenage.co.uk/optimmersion-links-solar-pv-and-the-immersion-heater/

 

[Grant_]

That's what I'm thinking.

But either way I need to get power to the immersion which is currently disconnected. I assume the solar controllers like the iboost or Eddi just get fitted in line and then use a CT on the main cable and just switch on the immersion when the inverter starts exporting.

Just had a look at my CU.
Among other things there is a 32a circuit labelled cooker. The cooker and ovens are gas. And one marked heating but I know that when the guy installed the boiler & did an earth test it triped the MCB for the sockets in the kitchen.

So yeah might leave connecting to the immersion to someone who can figure out what the fk is going on

If you are having solar installed it is possible to get a device which uses the surplus electricity from your solar panels to heat your water. This ensures that you use more of the power that you are generating and store it as heat in your hot water tank, effectively getting some free hot water. See here for information (just an example of what can be done): https://www.thegreenage.co.uk/optimmersion-links-solar-pv-and-the-immersion-heater/

 

[JohnD]

it's possible, but, unless you have no gas and are compelled to use electricity to heat your water, it is not a good investment

It might save you about half your HW electricity during the summer months

but if you are heating the cylinder with gas, it might cost you around 0.5 cu.m/day (about 5.5kWh)

Because energy from gas is so cheap, the cost of the gas is only about 3.5p per kWh

So your summer usage for hot water by gas is about 20p

of which (due to cloudy days) you might save half

so if this averages over 6 months of the year

365 divided by 2 = 183 days

at 10p gas saving per day = £18.30 per year

buying and installing the device will cost you at least £250

So after thirteen and a half years (if it lasts that long) you will stop being out of pocket, and will be as well off as if you had never bought it

Savings quoted by the sellers try to convince you that you are saving 20p per kWh

But that is only the case if you are unlucky enough to live in an all-electric home.

The document linked by pcaouolte incorrectly says "When you have solar PV installed, you benefit from the Government’s feed-in tariff which pays you for every unit of electricity you produce. This is known as the generation tariff, and currently the rate is just over 14p / kWh "

This is not true.

 

[AndyPRK]

The point is when you have excess solar electricity you heat your hot water for free.

 

[JohnD]

yes, except that "free" disregards the £250 or more you have spent on a gadget to save you 10p.

not a good investment.

If you give me £250, I promise to send you payments of £9 twice a year for the next ten years.

Deal?

I'll be the winner.

 

[AndyPRK]

Fair enough. Didn’t know they were that expensive.


I’ve got my daily gas costs over summer. (Somewhere) Im fairly sure it costs more than 20p a day!

And gas is only connected to boiler and costs nearer 2p kWh

 

[Grant_]

Yeah that's true.
But what I might do if the inverter/ generation meter support mqtt use home assistant to trigger a Shelly or sonoff relay when there is excess solar.

I know the fit is gone & current export tarriffs are around 5p/KW so it makes sence to use as much as I can

Daily gas usage at the moment on days without a lot of cooking is 60-90p but gas prices are predicted to rise especially if they stick to no new gas boilers in 2025.

 

[AndyPRK]

So you won’t be able to buy a gas boiler after 2025?
Any exemptions ?

Better order a couple

 

[JohnD]

I’ve got my daily gas costs over summer. (Somewhere) Im fairly sure it costs more than 20p a day!

Yes, there will be a daily standing charge, and this does not reduce when you reduce your gas usage.


My current tariff is

Gas:
3.21p/kWh (it was 2.48 until this month)
Standing charge: 26.78p/day

Electricity:
17.98p/kWh (it was 12.49 until this month)
Standing charge: 28.34p/day

But yours is probably different

 

[AndyPRK]

I wasn’t including the standing charge.
I’ll have a look on my spreadsheet when I can

 

[JohnD]

What colour HW cylinder have you got?