Been a while since I've done any heating work tbh. How much would you charge to replace a circulating pump (easy to get to, in an airing cupboard with space all around), replace a HW motorised zone valve (in same airing cupboard) and a unvented cylinder thermostat plus the immersion heater? A neglected system shall we say. There are so many reasons why the boiler is not firing on this S-plan system!!