Twice a year: water and seals
Find and turn your internal stopcock so it does not seize. Check under every sink and behind the washing machine for early staining. Inspect silicone around baths, trays and worktops and renew anything perished.
Run rarely used taps and flush rarely used toilets to keep traps full and stop drain smells.
Autumn: water going where it should
Clear gutters and check downpipes discharge into the drain rather than against the wall. Check gully grates are clear. Look for slipped tiles and lifted flashing from ground level.
Most internal damp we see in winter starts as an external water path problem in autumn.
Winter: freeze protection
Lag exposed pipework in lofts, garages and outbuildings. Isolate and drain outside taps. If you leave the property empty in cold weather, leave low background heating on rather than turning everything off.
Know where the stopcock is before you need it in the dark.
Spring: ventilation and wear
Test extractor fans by holding a sheet of paper to the grille - if it does not hold, the fan is not moving air. Clean fan grilles and check duct runs where accessible.
Check door and window operation, easing anything that has moved over winter, and touch up any external timber before summer.