Avoiding overloading house circuits

[Steve Hart]

Can anyone give me a steer on the following please?
I am installing an electric flow CH boiler (made by Heatrae Sadie). The unit I need for my house is rated at 9Kw. As I don't have a spare slot in my existing CU my plan is to install a separate CU (a 50A model sold as a 'shower CU') and wire it off existing Henley blocks with a further isolator by the boiler itself (which is about 5m from the CU).
If any of that sounds dumb please shout but my main question is that aside from the usual power sockets, light circuits etc (quite a small house - 2 bedrooms) I also have a 32A circuit with a 3Kw immersion heater (the boiler will only be for CH). a 45A circuit with a cooker and hob (which at full pelt could draw 9kw) and a 32A circuit to a 5.5kw electric kiln (my wife is into pottery). I'm going to have a professional come in to take a look but what are my options to ensure this doesn't overload? The boiler can be fitted with a relay so that, say, the electric kiln doesn't kick in when the boiler is firing but this might not be convenient and I wondered if even with that I would still have a potential overlaod issue?
Comments gratefully received.
Steve

 

[plugwash]

someone who just noticed that electic boilers draw a lot of power

personally i would just connect it up for now
if you do end up blowing the service fuse then while the rec guy is out to replace it talk to him about upgradeing to a 3 phase supply

 

[Steve Hart]

Thanks Plugwash. The problem with that approach though is that it might blow at any time - like in the middle of Xmas lunch for example? - which would be a major hassle. If I add up the boiler, kiln, cooker and hob load it would definately blow a 100A service fuse wouldn't it? If I put that to the rec would their response be to say they'll convert the house to 3 Phase (ie thats the only option) and if they did I'm not sure what impact that has on my existing wiring or the cost of the installation? My existing supply is via a overhead line.
Cheers
Steve.

 

[plugwash]

well you probablly only wan't to run you boiler at night anyway for cost reasons and you are unlikely to be running the cooker at night boiler+kiln+immersion is still under 100A afaict

as for moving to 3 phase i think you are looking at £1K-£2K from the rec and another grand to get you CU replaced with a 3 phase DB

 

[Steve Hart]

OK mate, thanks for the advice. Having to upgrade to 3Phase sounds worth avoiding for cost reasons alone