Most leaking uPVC windows are caused by blocked drainage slots in the frame, failed sealant between the frame and the wall, worn or displaced gaskets and weather seals, or a sash that no longer closes tightly. We check each route, find where the water is actually coming in, and repair it. Sometimes water that looks like a leak is condensation, and we will tell you if that is the case.
Is it a leak or condensation?
Before anything else, it is worth ruling out condensation. Water running down the room side of the glass and pooling on the sill on cold mornings, with no rain needed, is condensation from humid indoor air. It is not a window fault, and better ventilation, open trickle vents and less moisture indoors are the answer. Water that appears during or after rain, especially wind-driven rain from one direction, and that comes from the frame, the corners or below the window, is far more likely to be a leak.
If you see mist between the two panes of glass, that is a separate fault: a failed sealed unit, dealt with on our misted double glazing repair page.
Where do window leaks come from?
| Route | What you might notice | Usual fix |
|---|---|---|
| Blocked drainage slots | Water standing in the bottom of the frame, overflowing onto the inside sill in heavy rain | Clear the drainage channels; check the drainage covers outside |
| Failed perimeter sealant | Damp on the reveal or wall beside or below the window; cracked or missing silicone outside | Remove old sealant and reseal the frame to the wall |
| Worn gaskets or weather seals | Water around the sash or the edge of the glass, often with draughts | Replace seals and gaskets |
| Sash not compressing its seals | Leak on one side only; window rattles or feels loose when locked | Adjust or replace hinges and keeps |
| Joints in the frame or sill | Water at the corners or where the sill meets the frame | Reseal joints; check end caps on the sill |
How uPVC window drainage works
uPVC windows are designed to let a little water in past the outer seal and then drain it away. Water that gets into the bottom of the frame runs out through small slots, usually covered by little hooded caps on the outside face. If those slots are blocked with dirt, insects or old paint, the water has nowhere to go. It sits in the frame, can overflow inwards, and over time can sit against the edge seal of the glass unit, which is one of the reasons sealed units fail.
This is something you can check yourself. With the window open, look along the bottom of the frame for slots and gently clear them with a soft brush or a pipe cleaner. Only do this on windows you can reach safely from inside or from the ground; leave upstairs windows that need a ladder to us.
How we track down and fix a leak
- We ask when it leaks. Only in heavy rain, only with wind from one side, or all the time? The pattern often points to the cause before we arrive.
- We inspect inside and out. Drainage slots, external sealant, the sill, gaskets, seals and how the sash closes.
- We test where we can. Running water over a section at a time can help confirm the route.
- We explain and quote. You get a written quote for the repair that matches what we found.
- We repair and check. Clearing drainage, resealing, replacing seals or adjusting the sash, and checking the window closes and locks tightly.
If water is getting into the wall around the window, the cause might be outside our scope: a failed lintel, cavity tray, rendering or brickwork problem. We will tell you if the window is not the source, rather than resealing it and leaving the real problem in place.
Leaking windows in Liverpool's weather
We repair leaking windows across Liverpool and Merseyside. Homes facing the sea in Crosby and Wallasey take a lot of wind-driven rain, which is a hard test for sealant, seals and drainage. Older terraces in places like Birkenhead, where uPVC windows were fitted into older openings, can also have sealant and sill details that have not aged well. This is a common part of our work on double glazing repair in Liverpool, and often goes hand in hand with window seal replacement.
What affects the cost of fixing a leak?
Clearing drainage is usually a quick job. Resealing the outside of a frame depends on the size of the window, access and height. Replacing seals and gaskets depends on how much needs renewing, and hinge or keep adjustment adds a little more. Upstairs windows that cannot be reached safely from inside may need access equipment. We quote after seeing the window.
Window letting water in?
Tell us when it leaks and where the water appears. Call 07777 659786 or leave your details and we will call you back about window and door repairs across Merseyside.
Frequently asked questions
Why is my uPVC window leaking when it rains?
The most common causes are blocked drainage slots in the bottom of the frame, cracked or missing sealant between the frame and the wall, worn gaskets or weather seals, and a sash that no longer closes tightly. The pattern of the leak, such as only in wind from one side, usually helps narrow it down.
Can I just put silicone around a leaking window?
Silicone in the wrong place can make things worse, for example by blocking drainage slots or sealing water into the frame. If the leak is from failed perimeter sealant, resealing that joint properly is the right fix. If it is from drainage or seals, more silicone will not help. It is worth finding the route first.
How do I clear the drainage holes in my window?
Open the window and look along the bottom of the frame for small slots. Gently clear any dirt with a soft brush or pipe cleaner, and check the hooded caps on the outside are not blocked. Only do this where you can reach safely; leave upstairs windows that need a ladder to a professional.
Is water on my window sill in the morning a leak?
Usually not. Water running down the inside of the glass on cold mornings, without rain, is condensation from humid indoor air. Better ventilation, open trickle vents and reducing moisture from drying clothes and cooking help. A leak normally appears during or after rain and comes from the frame or the wall around it.
Can a leaking window cause the glass to mist up?
It can contribute. If water sits in the bottom of the frame because the drainage is blocked, the edge of the sealed glass unit spends long periods wet, which can help the edge seal fail. Once mist appears between the panes, the unit needs replacing, but clearing the drainage helps protect the new one.