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Central Heating Wiring - That Cant be Right - Adding a iBoost

Postby alewater » Fri Feb 26, 2021 9:36 pm

Hi,

I've had PV solar panels for a while now and finally brought a solar iboost to divert the excess solar generated towards the immersion heater. I'm fairly confident when it comes to diy and electrics but with this, I'm stuck. I feel like I have more wires than are needed and it just doesn't make any sense. How and where can I install my iboost system, and most importantly, how can I make my system safe?

My house previously had a back boiler which was removed 20+ years ago. It looks like I have an S plan system with two valves (one HW and one CH), and I have a Hive active heating so no thermostat on the wall.

In the airing cupboard there is a plug socket and the plug in the socket powers the wiring centre (that can't be right can it?). If I turn that off, it obviously turns everything off.

Rather than going to its own fused spur my immersion element has a standard 3 pin plug which I'm assuming if the central heating system went down I could just swap over and get hot water (never needed to do that).

There is a blank plate to the right and inside is a chocblock with one cable coming into the back of back box and the other exiting the left side (as seen in pic). This cable is live and when I took the conduit face off I found the other end just hanging there!!!! WTF!!!.

There are two white cables that come from under the floor to the left, and another that's behind the tank which goes to the central unit. Sorry the camera angle was bad so I drew the cable in the pic.

I've uploaded a video of the mess. https://youtu.be/vCJqviFU04A

Any ideas are welcome.
Thanks
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Postby ericmark » Sat Feb 27, 2021 1:37 pm

I don't know how the iboost works, I assume some sensor to show when over 3 kW is being exported which switches it on, and some sensor (likely same one) to say using current from the DNO to turn it off.

I can't see how as set up that links into central heating.

There are systems like this [attachment=0]Torrent pipe example.PNG[/attachment] where multi energy sources combine, but the heat store may use water but is not a simple cistern, it is rather special. But for what you have can't see how the central heating has any connection with the iboost the only connection is you likely want to keep water at 60 degs only with central heating so there is an option for the immersion heating to lift it to 80 degs.

You do seem to realise the existing system is in a real mess, for the extended time an immersion heater can run for the 13 amp fuse in the plug can over heat, less likely with the now no longer permitted plug you show with no pin insulators, but normally there will be a dedicated supply for an immersion heater and if plugged in a 15 amp unfused plug is used and the MCB/fuse in the consumer unit/fuse box is either 15 or 16 amp, so the plug will not over heat, today using a FCU is more common, so the fuse can cool by transferring heat to a larger unit. All fuses get hot, that is how they work the melt the wire inside.

I am sure you realise that wiring needs a lot of tiding up.

Theory is a solar panel should supply around 7 kW, in practice that is rarely the case, early solar panels were not metered, and the owner got a payment assuming they were pushing a fixed amount into the national grid, and so using the power produced by the solar panels was free energy, today the rates paid has dropped and the panels are metered, how they are metered not so sure, but with solar power often being less than 3 kW a 3 kW immersion heater is likely too big, I have seen systems with three 1 kW immersion heaters which came on and off as the supply from panels altered.

But as to if some thing like iboost works is down to both the tariff and the efficiency of the panels.

My bother-in-law had twin tanks like shown in his last house, solar water, solar electric, solid fuel, and LPG could all heat the water store, and with central heating turned to 12 degs C when he visited Germany for weeks at a time, the heating cost nothing and he had two hot tanks which could reheat house to 20 degs C before his return using geofencing.

However he has not installed it in his new house, main reason it costs around £20k to install. And that will pay for his oil until the day he dies with loads left over, so simply no point. The major cost is to reinforce the floor to take the weight of the storage tanks, his last house it was installed from new.

So I did look for iboost but only found adverts to sell it, did not find anything on how installed, I know the building management system in brother-in-laws old house was rather complex, it needed to insure if a fire is lit, then the water does not boil, even if there is a power cut. This should not be a problem for you, water needs to be less than 20 or more than 60 degs to avoid legionnaires, but other than that no real problem using solar to heat domestic hot water.
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Postby alewater » Sat Feb 27, 2021 1:52 pm

Hi Eric,
Thanks for getting back to me.

The solar iboost is only for heating hot water when the house is generating surplus energy. I've been tracking my solar generation and energy use for the last 4 years and I'm generating surplus power at least 1.5kw for long enough time each day (minus late Nov - lat Mar) to make it worth it.

To install the iboost in a "normal" set up is relatively easy, https://www.youtube.com/watch?v=y2a9Z-L0i5k. My wiring on the other day doesn't look anything like it.

This relates to central heating because it's the central heating wiring that a mess and I can't figure out what is what. 4 Cables coming in plus the old cable that's not been terminated.

Thanks
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Postby alewater » Sat Feb 27, 2021 10:59 pm

Done some more research and I’ve got a dual channel system which is the two white cables that come up from the left.

It looks like I’ve got a 12 connector block where ‘normal’ diagrams only have 10 and the L, N and E are in the incorrect order.

Any advice on how to wire the iboost?
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Postby ericmark » Sun Feb 28, 2021 5:16 pm

OK watched video and there is no connection to central heating, it should turn on the immersion when exporting over 3 kW and turn it off when under 3 kW.

However as an electrician I can see a flaw. A clamp on ammeter measures amps, but it can't measure the direction of current flow, it is AC so to know which direction current is flowing you need to measure volt drop over a resistor, so if volts higher on consumer side your exporting and if volts higher on DNO side importing, the question is of course can the DNO meter detect if importing or exporting power?

So if when iBoost switches on the current decreases then exporting and if it increases then importing so the iBoost may detect this, so it could work.

However main point it has nothing to do with the central heating.
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Postby alewater » Sun Feb 28, 2021 6:46 pm

Hi Eric,

If I’ve posted this in the wrong place then please just say that. I posted it here because from my amature perspective my CH and HW all comes under the central heating title.

My question was about the wiring of my ‘central heating’ and to add a iboost to the ‘central heating’ wiring.

Thanks in advance
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Postby ericmark » Mon Mar 01, 2021 8:25 am

You want the dedicated supply to the immersion heater feeding the iboost and the immersion heater is fed from the iboost, it does not connect to any of the central heating valves or thermostats, it is completely independent.

As said it is not normal to plug in an immersion heater with 13A plug, 15 amp with no fuse yes, but not 13A, and since a 15 amp has no fuse, it will normally be feed from a 15A fuse or 16A MCB in the fuse box/consumer unit.

The regulations say in the appendix any fixed appliance over 2 kW should be on a dedicated supply, or other methods used to stop a prolonged over load, this tends to be ignored for washer/dryer or tumble drier, but ovens and immersion heaters are normally on their own supply.

Clearly if not dedicated then you don't want an immersion heater on a 32A ring final without some protection, so using a FCU would be normal method, but it depends where on the ring final, near centre of ring final not really a problem as reasonable even draw on both legs.
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Postby alewater » Mon Mar 01, 2021 3:43 pm

Thank you.
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