How to replace your double glazed window seals (and stop cold draughts)

Got double-glazed windows but still feeling cold draughts?
Central-heating boiler kicking in more times than it needs to?
Curtains moving even though the windows are shut?
Read on ↓
In this video I used a replacement rubber seal kit made by 'Stormguard' and was bought from Screwfix. Other DIY retailers are available.
If you can answer yes to all these questions then chances are your double-glazed windows are misbehaving. In the UK, the most common form of double-glazed windows are uPVC framed, sealed unit type with opening panels. The opening parts of the windows have thin extruded rubber seals that have an rectangular or 'squared oval' section shape with an arrow head retaining part which fits in a slot that is machined into the fixed part of the frame or on the opening part of the window - or sometimes both.
Over many cycles of opening and closing and umpteen British winters and summers, these seals can lose their springiness and flexibility - which causes them to flatten. This means there isn't enough surface contact to make an effective weather seal between the opening panel and the frame. Cold air can get in, warm air can escape so your heating bills go up because the room thermostat is forever kicking on the heating. In addition to a colder house, lack of seal contact pressure can allow dirt, grime and dust past the seals and into the house. Often a sign of this is a general build up of grime around the edge of the opening panels or window frame. You might also see more condensation and moisture build up around the sealed units where they meet the frame. This can also lead to black mildew/mould build up.
I used a Stormguard product because it matched the shape and type of seal used on my twenty year old windows. The actual frames and sealed glass units are perfect so it was just a case of replacing seals.
Another top tip:
Most window locking mechanisms can be adjusted using an allen key so they force the window to clamp tighter on the seal. This is fine so long as the seal isn't split, perished and is still springy.
Please note:
I'm well aware that the windows needed cleaning. This was a quick n' dirty video for the real world because at the time my garden was undergoing hard landscaping and was essentially a big dusty building site so there was no point cleaning the windows until all the stone cutting and cement mixing was completed.