I am still looking into installing a combi boiler. the house is 4 bed detached with 11 radiators and one bathroom. I am looking at vaillant ecotec plus 837 or 831, ecotec exclusive 832 or 838 and worcester bosch cdi 30 or 37. Any views on which is best make, which size to go for. The ecotec exclusive seems quite large, is there much difference in performance to the ecotec plus models?