condensation
"Have had the heating on in the house for 5-6 weeks, cycling it on and off over the entire day, must have been on in total for 6-8 hours a day so i am pretty confident that the house itself is dried out.. "
Did you also have good ventilation? Remember, when you heat up air, it holds a lot more moisture, but when it cools down again, that moisture must condense and form droplets. Merely heating a house won't dry it out - only removing moisture will do that - and the only handy way to remove moisture is with ventilation (OR of course with a dehumidifier). If you are relying on ventilation to dry the house, warmed moisture laden air goes out, cooler dryer air comes in, the "new" air picks up heat and moisture and goes out..... and so on. Heating on its own just holds moisture in the air but doesn't actually get rid of it.