Maintaining an electric rooflight mechanism

What actually wears on a powered rooflight

A domestic unit on a ventilation programme might open and close twice a day through the summer and a good deal less in winter, so call it three to five hundred cycles a year. That is a light duty by any mechanical standard.

The parts that show it, in order, are the gaskets, which take a compression load every single cycle; the chain and its guide, which collect dust and lose their lubricant film; the hinge or friction stay, which carries the whole sash weight; and the cells in whatever is powering the controls. The motor and the gearbox are usually the last things to give trouble and often outlast the glass above them. The mechanics of the drive itself are described on the actuator page.

Cleaning the glass without putting a load on the mechanism

The order matters. Wash the glass with the sash held by the mechanism and you are pushing against a chain that was designed to pull, and on a centre pivot you may be pushing the sash past the position the drive is holding.

On a centre pivot the correct sequence is to drive the sash to its open position, release the manual catch, rotate the sash through 180 degrees and lock it on the barrel bolt. The outer face is then in front of you and the mechanism is carrying nothing. Wash, dry, unlock, rotate back and re-engage before driving the unit closed.

On a top hung sash the outer face cannot be reached from inside at all, which is why a self cleaning coating is worth specifying on any top hung or high level unit at order stage. Warm water and a little detergent is all that is wanted. Solvents and abrasive creams take the surface off a coating and off a powder coated frame.

The chain, its travel, and the brackets it pulls against

Once a year, watch a full cycle from start to finish rather than glancing at it.

The chain should emerge straight from its housing without deflecting sideways, run out to full stroke without hesitating, and retract at an even speed. Any pause, any change in note from the motor, or any sideways deflection means the sash and the frame have moved relative to one another and the geometry is no longer square.

The closed position is the more important half. With the sash driven fully shut, draw a strip of paper out from between sash and frame at each corner and at the middle of each side. The resistance should be even everywhere. Slack at one bottom corner is the classic finding and it points at the hinge rather than the chain. Slack all round means the closed position has drifted and wants resetting, which is an adjustment at the sash bracket rather than anything done to the motor.

The other half of the same check is the fixings. The chain pulls the whole sash weight through two small brackets, one on the frame head and one on the sash, and those fixings sit in timber.

The annual check is to grip the sash bracket and try to move it. There should be nothing. Any perceptible movement means a screw has begun to work in its hole, and the correct response is to deal with it while it is still a loose screw rather than after the fixing has enlarged its hole. Where a screw no longer bites, the fixing is remade into sound timber rather than driven harder.

Timber that has gone soft under a bracket is a different finding. A soft top rail means water has been getting past the glazing bead, and that changes the recommendation for the whole unit.

Lubrication, and what belongs where

Less than people think, and the wrong product is worse than none.

The hinge or friction stay takes a light machine oil or a dry film lubricant, applied sparingly to the moving surfaces and the excess wiped away. The chain guide takes whatever the manufacturer specifies, which on many ranges is nothing at all, because the chain runs on a low friction moulding designed to be dry. Adding oil to a dry guide turns dust into a paste and increases the load rather than reducing it.

Three things to keep away from the mechanism. Aerosol water dispersants, which strip the existing film and leave very little behind. Heavy greases, which collect grit. And anything sprayed near the gaskets, because oil swells rubber and a swollen gasket will not compress evenly.

Hinges, friction stays and a sash that has begun to drop

A dropped sash is the most common mechanical finding on any roof window and it is worth catching early.

The symptom is a gap that is wider at one top corner than the other with the sash closed, or a sash that catches on the frame on its way in. The cause is wear in the hinge or, on a top hung unit, in the friction stay. Most ranges allow a degree of adjustment through the hinge fixings, and where the sash is only a millimetre or two out that adjustment is enough.

Where the wear has gone further the hinge or stay is renewed as a part, which is a routine piece of work on a reachable unit. What matters is not letting a powered unit run for years with a dropped sash, because the chain is then pulling the sash into a frame it no longer matches and the load falls on one bracket.

Gaskets, and where they fail first

The gasket is a moulded rubber or thermoplastic section in a groove around the sash, and it is compressed against the frame every time the unit closes. Two decades of ultraviolet through the glass above it, daily compression, and the temperature range a roof sees will eventually harden it.

Perished gasket shows as a section that no longer springs back after the sash is opened, a visible flat, cracking at the corner mitres, or a draught you can feel on a windy night. Corners go first because that is where the section is joined and where it takes the most distortion.

Gaskets are supplied as a part by size code and renewing them is straightforward on a reachable unit. Doing it before the winter rather than after is the sensible order, because a hardened gasket in December is a cold gap on the coldest surface in the room and condensation follows it within days.

The drainage channel in the frame, and what fills it in a vale winter

Every manufactured roof window has a drainage channel in the frame that collects the small amount of water crossing the outer seal and takes it back out below the sash. It works perfectly and it works only while it is clear.

In Gloucester and the vale villages that channel collects leaf fragments in November, moss debris from the covering above it through the winter, and a fine silt from a roof that has been dry for weeks and then rained on. Under trees it fills faster. Once it holds standing water, that water sits against the bottom of the sash, and on a powered unit that is closing hard onto its seal in all weathers it has nowhere to go.

Clearing it is a soft brush and a wipe with the sash open, twice a year, and it is the single most valuable five minutes on the list.

The ventilation flap filter, and the mesh behind it

A powered unit still has a background ventilation flap in the top rail, with a filter behind it, and it loads exactly as it does on a manual unit.

The annual task is to unclip the cover strip along the top rail, draw the filter out of its slot, wash it in warm water with a little detergent, squeeze it out rather than wringing it, and let it dry completely before it goes back. While the cover is off, the internal chamber gets wiped and the external slot and its insect mesh get a soft brush and a vacuum nozzle. Autumn is the right time, once the pollen and seed season has finished.

The detail behind all of that, including what equivalent area a loaded filter costs you, is on the ventilation flaps and filters page.

Cells in handsets and wall controls

A handset that has stopped working has almost always run its cells down, and it is worth exhausting that before anything else is suspected.

Most handsets take a pair of AAA or a coin cell and last one to two years in normal use. Wall pads run longer where they are wired and about the same where they are not. The symptom of a dying cell is not a dead control but an unreliable one: it works from a metre away and not from across the landing, because the transmitter power has fallen while the indicator light still comes on.

Two practical points. Renew the cells in every control at the same time, so they are all on the same clock. And keep the pairing instructions with the Building Control paperwork, because a control that loses its pairing during a cell change needs re-pairing, and the sequence differs between systems. The controls page covers what each type does.

The battery in a solar unit, and what to expect from it

A solar operated rooflight carries a rechargeable pack in the sash, charged by a small module on the outside of the top rail, and it is a consumable with a long but finite life.

Manufacturers commonly quote something in the region of a decade before capacity has fallen far enough to matter, and the first symptom is behavioural rather than total: the unit works normally in June and becomes hesitant in January, because a short day on a north facing Forest of Dean slope is not putting much back in. Cold makes it worse, since capacity falls with temperature.

The module face wants cleaning at the same time as the glass, because a film of dust or a growth of moss along the top rail cuts the charge current before anything else does. Renewing the pack is a part swap on a reachable unit and a tower job on a stairwell, which is worth knowing at specification stage rather than a decade later.

Sensor faces, and the film that stops them reading

A rain sensor works by detecting water on a small conductive or optical face on the outside of the sash, and it reads what is on that face rather than what is in the sky.

Three things interfere with it. A film of grime, which holds moisture after the rain has stopped and keeps the unit shut for hours longer than it should. Bird droppings, which do the same thing permanently until removed. And a build up of limescale on the face itself in hard water areas, which most of Gloucestershire is, deposited every time a drop dries on it.

A quarterly wipe with a damp cloth is all it takes. A humidity sensor inside the room has the same problem in a different form: its grille collects dust and lint, the reading lags, and the unit opens later than it should. What the sensors are actually doing is set out on the rain sensor page.

Electrical checks, and the part a qualified electrician carries out

Everything above is mechanical and can be done by a householder on a reachable unit. The supply side is separate.

A mains fed rooflight system sits on a circuit like any other, and it is included in the periodic inspection and testing of the installation as a whole. Any alteration to that circuit, any new spur, and any work at the consumer unit is carried out by a qualified electrician, and is notifiable under Part P where applicable. The transformer or control unit itself wants nothing beyond being kept dry, ventilated and free of stored boxes piled against it in a loft void, which happens more often than you would think.

Where a system was installed with a backup pack, the pack is the item with the shortest life on the electrical side. That subject is covered on the backup power page.

Spring and autumn: two visits that suit the Gloucestershire year

The timing is not arbitrary. Two visits fall naturally.

Autumn, before the weather turns. Filter washed, mesh cleared, drainage channel cleaned out after the leaf fall, gaskets checked and any hardened section renewed, closed position verified, cells renewed. The object is a unit that will be shut and sealed for four months and needs to be genuinely shut.

Spring, before the unit goes back into use. Glass washed inside and out, sensor faces cleaned, a full cycle run and watched, hinge lubricated, and the summer ventilation programme set. On a vale property this is also when the winter’s moss debris comes out of the channel, and in the Forest and the Stroud valleys there is usually more of it than in the city.