Please help, am in desperate position, no heating, extremely worried. Potterton Lynx 2 combi just had annual BG service after insurance renovation work in basement flat because of 'Escape of Water' damage from rising main. The system had been in full working order at time of investigation of leak which turned out to be rising main (not central heating related, which was tested at the time, good sustainable pressure, about 1.5 bar). All radiators had been removed to repair rising damp/rot in walls and floors, one replaced in the bathroom, 21mm marine ply subfloor and expensive 21mm hardwood floor laid on top throughout flat. During refitting of radiators, 2 had leaky valves which were fixed, but the system was not checked as fully working before contractors left or before the hardwood floor was laid by another company. Within hours of the boiler service (after the floor was laid!!!), system cut out to 0 bar pressure, no heat no water, even on reset. Second BG engineer refilled system at filling loop, replaced ISO valves which had slight dripping leak (left them in permanently open - vertical - position), fitted new ignition lead which had corroded, left the pressure at 1.5 bar, boiler cut out within hours. Third engineer checked pressure release valve, dismantled it and flushed it through (no problem), replaced expansion vessel (which was full of black gunk), was going to change coupling loop but toby outside is seized in this perishing weather so couldn't isolate water supply in the flat. B Gas say boiler is on 'restricted parts' but still serviceable within their Homecare 200 plan, even though third engineer got me to sign Safety Warning saying 'Boiler/Kitchen/Terminal Position' !!!! I assume that means it's becoming too expensive for them to service or find the fault, even though I've been paying up for 8 years and no call outs. Kept an eye on the pressure gauge and it steadily rises to 2 bar then boiler shuts off and I have to reset every 40 minutes. All radiator valves at high, all bled, all dry at the valves (no leaks above floor), all heat up very quickly and no cold spots at bottom or top. Last engineer suggested magiclean flush of system, or maybe there is a subfloor leak, maybe a floorboard nail or screw only slightly lodged in a pipe. Question: are there any other things that could be going wrong in the boiler to go to high pressure, shut off, then reset light come on? If I don't reset, it eventually goes to Low Pressure warning light and 0 bar on gauge; same when it is switched off. I seriously don't want to lift this floor and subfloor again to find possible leak, an insurance nightmare on top of an already 7 month insurance and botched jobs nightmare. There have been three main contractors on the job, two of whom have worked on the radiators and valves, but any one of many workers could have accidentally lodged a nail or screw sub floor into pipes, or it could be a slow leak at the new bathrooom radiator valves which were sectioned on sub floor. Surely, this must come under Accidental Damage within the existing claim on Buildings Insurance which is already picking up the bill for the original repairs? There has been only one 5 minute visit from a Contract Manager at the beginning of stripping out work (no central heating pipes were replaced or lifted). I can see this getting bogged down by the Loss Adjuster in legal claims about liability when all I want is my flat back with the working Central Heating System it had at the outset!!! Please tell me it might still be the boiler. Thanks, and sorry for long post.