Basics. 190m2 single storey UFH throughout.  UFH pipes at 300mm centres.  House heat load max 3kW.   Atag A325ECX combi boiler min turndown 6kW.   160l buffer, utilising an unvented thermal store with indirect boiler coil and DHW coil.  Summertime use is for excess solar from PV to heat tank and use instead of boiler for DHW.   Issue 1, when used at low temperatures the heating coil is way to small, had to turn boiler up to around 50 deg flow temp to get the bu