I am ACS qualified but with little experience as yet and have just started working for a property management company based in Halifax. In the last 2 weeks i have been to 2 fairly new converted mills that both have Ideal mini boilers in them and neither will work on CH but both work OK on DHW. Any ideas? both room stats are on full and all rad valves and TRVs are open fully and there is 1.5 bar pressure in both boilers. Manual gives no clues. Both boilers are approx 2 years old and have had no more than 6 months use as both flats are empty.