Hello ,I have an alpha cd35c combi boiler fitted with alpha gas save unit. It is 5 years old and under an ;8 year warranty subject to annual servicing by alpha installer. All services have been carried out. The boiler works well apart from persistent de pr essuring problems. This has happened from new and always happens with the first cold weather usually in October. It is easily re pressurised. The time between re pressuring reduces with each re pressuring from about 10 days to about every 2 days. In spring 2016 a new expansion chamber, pressure valve and filler loop were fitted. It worked perfectly from then until the end of October but is now needing re pressuring every 2 days. Over the years occasional leak sealer has been added to the system . There are no obvious leaks on radiators etc. I have also noted that when I 're pressure to the green when the boiler is working the pressure is quickly up to the red zone. Any ideas ?