Hi - have vaillant thermo-compact 615E system boiler approx 4 yeras old, been fitted 2.5yrs and has only been operational for 12months (1 day a week as property has been empty undergoing refurbishment). During times of operation boiler has worked perfectly for both hot water and central heating. Prior to renting of property, landlords gas safety certificate was obtained last thursday when corgi registered operative serviced boiler and carried out necessary checks etc. Since service the boiler has been displaying fault code F22 (No / Low water in system) every day. On turning off and on, the boiler works seemingly perfectly for approx 24hrs before fault code F22 reappears and off we go again. pressure gauge is set at 1.5bar and has remained so throughout display of fault code - so no lack of water as is reported. Trying to contact contractor who carried out service but in the meantime can anyone offer any ideas please as to possible problem. - Landlord to one unhappy tenant!