At least none as explained to me by a Honeywell tech when I was trying to get them to change a component with a burnt out 10amp relay while the system fuse was 3amp, the boiler fuse was 2amp and the control board was fitted with a 1amp fuse. Fuses protect against current not voltage surges which caused the problem here and another at a nursing home I looked after.
A socket circuit cable, for example, needs both, because you can overload it. A table lamp flex, as mentioned earlier, needs only fault protection, as that can't get overloaded.
Thinking about it... is it that CH wiring is more prone to heat damage from contact with hot pipes in airing cupboards etc and therefore needs a smaller fuse to shut off the supply if compromised!?
I'd be very wary of assuming loads cannot cause an overload condition unless the manufacturer states as such, or you can see that it incorporates its own protection against such a situation, with a boiler that could well be the case, it might have a fuse on the PCB, however its unlikely that pumps, motorised valves would be immune from an overcurrent fault, in a proper mechanical services panel you'd have an overload relay on the contactors for the pumps, but on a domestic type system theres nothing like that.
No but they do have different and often lower standards of safety and are more prone to "taking calculated risks" using a different set of formulas.
Germany had and may still have electric showers in domestic bathrooms with 3 phase heating elements. In 1971 the night storage heater in my apartment ( bed sitting room to be precise ) was three phase.
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