Hi all. Got the above combi which had an F25 (circulation) fault. Had new expansion vessell (was bad) then at advice of Glowworm a new diverter valve as hot water was OK but fault on heat. All has been perfect for a few weeks then back to F25. As before cutting power cures it. Always from cold. This time both HW and heat. The only catalyst this time is I turned down a radiator valve. Had a big bill last time so trying to pre-empt this time. Pump is very strong (screwdriver test).Thank you..