Many people think a combi boiler is not suitable for a large house, but is this right?
The reason for this is mostly out of date. Older combi boilers are not capable of heating up high volumes of hot water. This is because the boiler heats the water up instantly so needs to slow the water down to match the power and efficiency of the boiler. Huge improvements have been made on this front, very high powered options are now available (upwards of 40kw). This means that the boiler doesn’t need to slow the mains water down anything like the old boilers do so can cope much better with 2 water points running at the same time. The other possible reason Combi boilers did not used to be thought suitable is when the boiler is in hot water mode it turns off the central heating. However unless your consumption of hot water is very high the radiators are unlikely to cool before the boiler switches back to central heating mode.
In reality a high powered combi boiler is suitable for the vast majority of large homes, there are some properties which are better served with a unvented cylinder, but the number is continually reducing with the advancements in combi boilers.