It depends on the type of inner seal. Older ones have a removable rubber seal which can be teased out at a corner with a pair of needlenose pliers or strong tweezers. Once the seal is removed the plastic trim is easily removed by pushing it towards the glazing unit by applying pressure at the joint with the frame near the corner. Take note to remove the top piece last and if its a large pane have someone hold the unit in place from the inside. Newer and more common units have a combined seal and insert. These can be removed with a couple of 1" scraper/putty knives. Ideally they should have a keen edge. You carefully push the blade at the join between the frame and insert at a corner on one of the longer inserts strips (bottom if the loger ones are horizontal). Once in you lever the insert towards the glazing unit and away from the frame while applying firm pressure towards the glass to stop the blade popping out. It might take a couple of attempts. You should then be able to get the second knife into the gap between the frame and insert and lever it out taking care not to touch the edge of the glazing unit. In doing so the gap will move along the joint. It can then be further released by sliding one knife along the joint taking care to avoid it digging into the PVCu edges. I've found an old dinner knife does this very well. Once the first insert is out repeat the process for the other 3 taking care to ensure the glazing unit is supported for the last one. There will be a couple of plastic shim/inserts under the bottom of the unit. These help centre the galzing unit in the frame and may well need to be replaced with different sizes when you fit the new unit. Refitting is fairly easy for the older sepaerate seal and strip, the tricky bit is keeping the first one in place while the seal is slid back in. For newer combined ones you need to be brave! Start with the top insert/seal wipe the little lip that will go into the frame with silicone grease or washing up liquid. Push it into place at a corner, the lip can usually be squeezed in by pressing frimly down on the larger flat surface with thumbs, or with a rubber mallet or the rubber shaft handle of another tool. Once the first part is in place repeat for the other corner and then apply pressure the the rest of the insert starting from one of the attached corners and working towards the middle. Repeat for the other 3. Always fit one of the longer inserts last. I've done this several times not only to replace sealed units but also to temporarily remove glazed units for furniture removal. If you have a blown unit try to remove one of the insert strips and replace it before you order the new one, that way if you find it's difficult you will still have a secure window while you arrange for a glazier to do the job.
HalfEatenYorkie, May 2010
