Solved by installing PIV (Nuaire Drimaster), heating house properly, opening bathroom window after showering, cracking open windows occasionally where possible.
Not sure which of those things solved it, but all together they certainly did.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local