Over the years I've seen the growth of combination boilers and how they have overtaken system and heat only. While combination boilers have their uses, its becoming increasing frustrating why so many plumbers choose this option. Heat only is by far the cheapest and effective way to heat a home and provide hot water. They are more reliable and will save the customer 1000s in energy and repair bills over the life of the boiler and cylinder. Increasingly I'm seeing more homes choosing 45 plus KW combination boilers to deal with hot water demand. But the plumbers fail to grasp that most homes will only have 13 litres a minute supply so what good is 20 litres a minute at the boiler. Also they fail to consider the gas service as most properties will not have a 35mm service. It states clearly in the regs that service should be considered. It won't be long before transporters start charging to upgrade when pressure problems are reported. A good quality heat only boiler and 170litre unvented cylinder is OK for most homes. In most cases 24kw will do. I really don't get it the concept of ripping out a system to fit an inferior water heater that will only last 10 years.