C12awa

hi mate i have a problem with my valiant thermocompact boiler i have screed under floor heating down stairs and floating floor under floor heating up stairs i also have a hot water storage tank up stairs in loft and the boiler is in the kitchen now i use to loose water pressure on my boiler so i called valiant and they changed it the the expansion vessel the problem with loosing water pressure is fixed now boiler starterd to fire up even when the timer was switched off for water and heating and at night time my underfloor heating up stairs starterd making noises so i called them again and the came and changed the pump and the honeywell valves for under floor heating and put in new z6 divator valve and some other parts they took the boiler out side and changed a few other little bits and the boiler still keeps on firing and goes off with in 10 secs so i called them again now the say its the external wiring i have had a electrician and he confirms the wiring is ok as the boiler was fitted in 2004 and has been running very good i cant sleep at night because the pump over run wakes me up i will be very glad if you can help me please their are no fault codes on the boiler apart from first it says s2 s3 s4 and then boiler goes off and codes reads s7 when temp goes down it fires up again i have also lower my hot water tank thermostat to half