How to replace a roller shutter strap (with an internal box, without removing it)

What you need

• PZ2 Phillips screwdriver and a flat one
• Scissors or a craft knife
• Lighter to seal the ends of the strap
• Tape measure
• 3-step ladder
• Vacuum cleaner or brush to clean the box
• 14 mm or 22 mm shutter strap, 6 m roll (Gaviota, Wolfpack or Micel, 6-9 euros at Leroy Merlin or Bricodepot)
• Flush or surface-mounted strap winder if the spring is worn out (Gaviota Mini or Pujol, 8-12 euros)
• New plastic strap guide if the current one has a broken roller (2-3 euros)
• Wall plugs and 4 x 30 mm screws for the winder

Step by step

1. 1

   Lower the shutter fully and take a photo

   Leave the shutter completely down so the strap is under minimum tension. If the strap is already broken, lower the shutter by hand by pushing the slats down from the box. Photograph the route of the strap before touching anything.

2. 2

   Remove the winder

   Take off the winder cover (it clips on or has a central screw) and loosen the two side screws. Ease it out of its recess carefully: the spring may be under tension and spin suddenly. Release the end of the old strap from its hook or slot.

3. 3

   Open the box cover

   The inspection cover on an internal box is screwed or clipped to the front, just above the window. Remove the screws, take off the cover and vacuum out the sand and dust. Find the strap pulley: it is the plastic or metal disc at one end of the axle.

4. 4

   Remove the old strap and tie on the new one

   Unwind the old strap from the pulley and undo the knot or the clip. Seal the end of the new strap with the lighter so it does not fray, pass it through the slot in the pulley and tie a flat knot. If the pulley has a retaining clip, use that instead of the knot.

5. 5

   Wind the strap onto the pulley in the right direction

   With the shutter down, turn the pulley by hand and wind the strap in the same direction as the old one (look at the photo). Give it the number of turns needed for the height of the window plus two to spare: for 1.2 m high it is usually 4 or 5 turns on a 15 cm diameter pulley.

6. 6

   Pass the strap through the guide and down to the winder

   Drop the free end down through the gap in the box, pass it through the strap guide on the wall and take it to the winder recess. Check that the strap runs straight without twists; a twisted strap rubs and cuts through within a few months.

7. 7

   Tension the winder spring

   Hook the strap into the slot or hook on the winder and turn the reel in the direction of the arrow to tension the spring: 8-10 turns for a 1.2 m window, 12-14 for a balcony door. Hold the reel with your finger or the catch so it does not unwind.

8. 8

   Screw on the winder and test

   Place the winder in its recess without letting go of the reel, screw it in and fit the cover. Raise and lower the shutter three times: it should go up with a firm pull, stay in any position and retract the strap without it hanging. If it hangs, add 2 turns to the spring; if it pulls too hard, take 2 off.

9. 9

   Close the box

   Refit the inspection cover with its screws, without overtightening so you do not crack the PVC. Cut off the excess strap at the winder leaving 10 cm to spare and seal the end.

Before replacing the roller shutter strap: why it breaks and which one to buy

The shutter strap is a polyester or cotton belt that links the axle in the box to the winder on the wall. Every time you raise the shutter it winds onto the pulley on the axle, and every time you lower it, it retracts into the spring in the winder. Over time it rubs on the strap guide, frays at the edges and ends up snapping right where it bends most, almost always at the winder or inside the box.

On the coast the process is faster. Salt air dries out the fibre and the sun on south-facing terraces makes it brittle: a strap that lasts 10 years inland lasts 4 or 5 on the seafront in Torrevieja or Benidorm. Old cream-coloured cotton straps age worst; polyester ones with UV treatment hold up far better.

Before going to the shop, measure the width of the old strap. There are two standard sizes: 14 mm for PVC or light aluminium shutters up to 1.5 metres wide, and 22 mm for wide shutters, thick-slat shutters or timber ones. If you buy the 14 mm for a shutter that takes 22 mm, the winder does not grip it properly and the strap splits within months. The standard roll length is 6 metres, enough for any window or balcony door in a home.

• 14 mm strap: bedroom and kitchen windows, light shutter, small winder.
• 22 mm strap: living room balcony doors, shutters 2 metres or wider, foam-filled aluminium slats.
• If the old strap is over 25 mm, it is probably a belt from an old timber shutter; measure it and ask for the same.

Common mistakes when replacing a shutter strap

The most common mistake is winding the strap onto the pulley in the wrong direction. If the shutter goes up when you pull down but the strap crosses over and rubs, you have wound it backwards: undo it, reverse the direction and start again. Before removing the old strap, note how it enters the pulley, from the front or from behind, and take a photo with your phone.

The second mistake is not tensioning the spring enough. A winder with 3 or 4 turns of tension does not retract the strap and the shutter is left slack, with the strap hanging. For a 1.2 metre window you need 8 to 10 turns; for a 2.2 metre balcony door, 12 or 14. Overdo it and the spring breaks or the strap pulls up so hard you cannot hold it.

Other faults we see daily: leaving the end of the strap unsealed (it frays within weeks), tying a knot so thick it jams in the strap guide, screwing the winder into plasterboard without the right plug, and replacing the strap without first cleaning the pulley, which usually has a layer of dust and sand that wears out the new strap again.

When to call a professional

If, when you open the box, you see the plastic pulley is broken, the axle moves sideways or the slats are loose, the fault is no longer just the strap. The same if the shutter is heavier than normal or is foam-filled aluminium over 2.5 metres wide: the spring in a standard winder cannot hold it and you need a heavy-duty winder or a motor.

We replace the strap for 35-60 euros with materials and call-out included, and if the winder has to be replaced as well the total comes to between 45 and 70 euros. We arrive in 20-45 minutes in Valencia, Alicante, Torrevieja and Benidorm, and the repair takes 30-40 minutes. See all our shutter prices in how much it costs to repair a roller shutter or book on the roller shutter repair page.

If you live in the city of Valencia, we have a page with local times and prices at roller shutter repair in Valencia, and the same for Alicante and Torrevieja.

Tips for the coast: salt, sand and sun

In homes less than 2 kilometres from the sea we recommend a polyester strap, never cotton, and checking the box once a year. When you open the cover there is usually fine sand that has come in through the gaps in the box and settled on the pulley; it comes out with the vacuum cleaner and a dry cloth. Do not put grease or oil on the pulley or in the guides: it attracts the sand and forms a paste that scratches the slats.

If the shutter faces a south-facing terrace, the strap gets direct sun every time you leave it at half height. When you are not at home, leave it fully up or fully down, never halfway: that way the strap is stored in the winder or the box and not exposed. A new strap guide (2-3 euros at a hardware shop) with a smooth roller also extends the life of the strap considerably.

Related guides

If your shutter uses a cord instead of a flat strap, the process is different: we explain it in how to replace a roller shutter cord. And if after replacing the strap the shutter still does not go up properly, check the causes in my roller shutter will not go up or the summary of faults in how to fix a roller shutter.