When I last moved house, there was a potterton Flamingo on a fully pumped system with tap stat on the hot water vessel and zone valve with roomstat on the heating. Buget was limited and I did not want to give myself to much work to improve the system. I changed the boiler for a Vaillant 618 ecomax and put it in the roof with verticle flue, changed the hot water vessel for a quick heat recovery type, seperated the upstairs and ground floor heating circuits (new rads down stairs), fitted 3 zone valves for each circuit with thermostats linked through a timeclock and interlocked with the boiler, thermostatic rad valves on all rads. Result was reliable system and 25% saving tested over the last 7 years on fuel consumption. Would have liked to have fitted an unvented hot water system, but could not justify the additional cost. Didn't want a combi because the the old problem with getting cold shocks when someone draws off water when your in the shower. Also fitted a shower pump, which has been fantastic.