No, you can’t because power showers operate with a built-in pump and need to be connected to a hot water cylinder, which combi boilers don’t have. Thermostatic mixer showers are the best type of shower to have with a combi boiler because they guard against fluctuations in temperature if someone else switches on hot water while you are showering. Alternatively you can opt for an electric shower which does not impact on the boiler at all.