Window repair: fixing what is broken instead of replacing everything

Condensation between the two panes means the seal of the sealed glazing unit has failed. The frame is usually fine, and the unit alone can be measured, made and swapped. The same applies to a cracked pane. The repairer should match or improve the glass: toughened or laminated safety glass wherever it is required, such as in doors and low-level panes, and obscure glass where the old one was obscure.

GOV.UK lists most repairs and replacements as exempt from Building Regulations approval, but names glazing units as an exception, and FENSA says its scheme does not cover repairs where the frame is not included. Ask the repairer what standard the new unit meets and what paperwork you will get, so that nobody later questions a replaced unit.

On uPVC and aluminium casements, the friction hinges that hold the sash in position wear out, and the window drops, sticks or will not close tightly. Multi-point locking mechanisms inside the frame break, and handles fail. These parts are standard in size for most systems and can be replaced in a visit. Fitting escape hinges on an upstairs window is also a repair worth considering if the room relies on it for escape.

When a window cannot be locked, ask for a repair quickly: some home insurance policies limit theft cover where windows were not secured.

Box sash windows were designed to be maintained. Sash cords snap, weights drop, beads are painted shut and the sashes rattle. A joiner can strip the sashes out, renew cords and pulleys, ease the running, and fit draught-proofing brushes and seals into the beads. Rotten sections of sill or the bottom rail can be cut out and new timber spliced in, and joints can be re-glued rather than the whole sash remade.

Secondary glazing, a slim inner window fitted inside the reveal, adds warmth and reduces noise while the original sashes stay untouched. On a listed building, repair and secondary glazing are usually the routes the council's conservation officer expects, and changing the windows themselves normally needs listed building consent.

Repair is worthwhile when the frame is sound. If a timber frame is rotten through at several joints, a uPVC frame has distorted so that it no longer seals, or several parts fail at the same time on windows that are near the end of their life, replacing the window is more economical over the years. A repairer who does both will tell you which applies; one who only sells new windows may not.

Replacing the whole window, including the frame, is controlled work and should be done by an installer in a competent person scheme or approved by Building Control.

Most repairs are quoted faster with photographs. Useful things to send are a picture of the whole window from inside, a close-up of the fault, any branding on the frame or the spacer bar between the panes, and approximate sizes of the glass.

• the fault and the parts to be replaced, by window
• glass specification, including safety or obscure glass
• whether parts are in stock or have to be ordered
• for timber: extent of splicing, filling, reglazing and repainting
• draught-proofing or secondary glazing if requested
• guarantee on the new parts and on the labour

The request costs you nothing and reaches local window businesses without your name or number. One of them can buy it and pays Offrano for it; after that it is off the list. We tell you by email which business it is, with its address and phone number, before it gets your details.

Small repairs are not always taken up, and a request that nobody buys within 21 days is withdrawn. You never have to accept the price offered. Offrano confirms only that the buyer is a registered business, so ask about its experience with your type of window.