Elec combi boiler supply

RMS1981 · May 8, 2022

Hi all.
My mum has just moved into a flat and it has an electric central heating boiler and a hot water tank/immersion heater for the hot water. I’ve said will look into putting a combi boiler in to free up the space in the cupboard for a washer/dryer.

The flat is about 10 years old. The boiler is fed from a 32a MCB, but the combo’s seem to be around 14.4kW, so 63a needed. The main switch is 100a, so by my reckoning, it would need a separate CU installing. As long as what I’ve said so far sounds ok, the problem starts there. The electric meter isn’t inside the flat, but in a communal switch/meter room. I’m guessing that means we won’t be able to put in a parallel supply to another CU.

What would you normally do in this instance? Is it a question for the management company? Has anybody had any success in doing this? I could just put a 63a mcb in place of the 32 in the current CU, but I fear it might be overloading the main switch?

James · May 8, 2022

I think this project is beyond a bit of DIY advice.
I suggest you get an electrician round to quote, it will then be notified and signed off as safe.

Dartlec · May 8, 2022

RMS1981 said:
Hi all.
My mum has just moved into a flat and it has an electric central heating boiler and a hot water tank/immersion heater for the hot water. I’ve said will look into putting a combi boiler in to free up the space in the cupboard for a washer/dryer.

The flat is about 10 years old. The boiler is fed from a 32a MCB, but the combo’s seem to be around 14.4kW, so 63a needed. The main switch is 100a, so by my reckoning, it would need a separate CU installing. As long as what I’ve said so far sounds ok, the problem starts there. The electric meter isn’t inside the flat, but in a communal switch/meter room. I’m guessing that means we won’t be able to put in a parallel supply to another CU.

What would you normally do in this instance? Is it a question for the management company? Has anybody had any success in doing this? I could just put a 63a mcb in place of the 32 in the current CU, but I fear it might be overloading the main switch?

I assume you mean an electric combi boiler since you are quoting 14.4kW? I don't have any experience with them, though they do seem to vary in power requirements.

What is needed before it could be done though is an assessment of the load and the existing setup. The flat will have a main fuse somewhere (probably in the communal switch/meter room), which might well only be 63A or 80A by itself. That will be the limitation of the maximum load. The cable that runs to the flat from the switch room will have been sized accordingly, (and usually running a parallel supply is not an option.)

The projected load being used in the flat will require some experience and judgement as it can vary a lot depending on what other appliances are in place (cookers, showers etc) and based on the understanding that not everything will be on all the time etc. That will dictate what can be fed safely from the existing consumer unit (or perhaps a second CU) , though it's very unlikely that a 63A breaker will be an option.

You could certainly ask for the information as to the supply from the management company as it will be useful to any one giving a quote in the future. There might be a electrical certificate in the handover documents which would also be helpful.

Electric combi boilers are still a fairly specialised area so you may be best trying to get a quote to supply and fit from a suitable supplier (just ensure they will be using qualified electricians and providing documentation/certification)