I removed a Potterton combination boiler and installed an Atag A325EC high efficiency combination boiler. This boiler is the most efficient combination boiler due to its built-in flue gas saver. The flue gas saver recuperates the flue exhaust heat and utilises it. The Atag A325EC flue exhaust temperature averages around 20-30 degrees celcius whereas other condensing boilers flue exhaust temperatures average around 60-70 degrees celcius. The A325EC boiler is not suitable for any location due to its size 87cm high x 45cm wide x 38cm depth. I also installed an Atag Wize programmable modulating room thermostat and weather compensator control.