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This article is provided for information purposes only. You should only attempt any procedures explained here if you are competent to perform the task and have the appropriate tools and materials, including any relevant safety equipment.

Readers acting upon this article do so at their own risk and no responsibility is accepted by the author or publisher for any loss or damage incurred by following the article or failing to follow it.

If in doubt always consult a properly qualified tradesperson or other competent person.


A line strainer is a device to filter out grit and debris from a water line to protect appliances from being damaged by contamination.

Sometimes line strainers are integrated into other fittings to provide a combined function, such as the safety systems fitted to Unvented hot water cylinders. These often have a combined line strainer, non-return valve (called a 'check valve') and pressure reducing valve to control the water flow to the cylinder.


The line strainer is basically a metal or plastic mesh filter fitted inside a compression connector (see picture). Water passes through the mesh but particles of dirt and grit are trapped by the mesh.
line strainer


The design of individual line strainers may vary between manufacturers and between installations. Standalone line strainers tend to comprise a brass mounting with a mesh filter whereas line strainers incorporated in combination valves tend to be plastic.

Usually the mesh is detachable and mounted in a housing so that the mesh can be cleaned without removing the entire compression connector or combination valve.


(please read this article in full before attempting to clean a line strainer)
Eventually the grit and debris trapped by the mesh will slow down the water flow through the filter and, if left, it will block the filter completely.

To prevent this the line strainer should be cleaned periodically, certainly at least once each year and sometimes at more frequent intervals if the local water supply is prone to carrying sediment and grit.

How to dismantle the line strainer

Cleaning the line strainer will normally require the water flow to be isolated, so line strainers are typically fitted just after the main stop valve (or 'stopcock') for a property or just after a local isolation valve on a pipe run.

Put some clean cold water in a small container - you will need this to clean the line strainer. Turn off the water supply and turn on the next tap in line after the strainer (this might typically be the kitchen tap) to drain out local water.

Once the water flow from the tap has stopped, leave it turned on and go back to the linerstrainer.

Place a container under the line strainer to catch any water that escapes, then use a spanner to slowly unfasten the nut that holds in place the detachable mesh cartridge.

As you undo the nut wait for the local water to begin escaping from the line strainer and then stop and leave the line strainer to drain into the container until the water flow stops, then repeat the process of slowly unfastening the nut and draining off the water until the nut can be removed entirely without a sudden large flow of water from the line strainer.

There may be a fibre washer or rubber seal around the nut - keep this safe for refitting later.

Note the position of the mesh inside the housing in case it has a particular mounting point, then remove it and carefully clean the mesh in the cold water you have saved - use a small paint brush to gently brush away any trapped grit - make sure that you don't break the mesh as this will make the line strainer useless!

If the line strainer mesh has limescale deposits then clean it using a mild proprietary limescale remover or use lemon juice. Be careful not to use any cleaning agents on the seals or washers around the line strainer.


line strainer before cleaning


line strainer after cleaning

How to reassemble the line strainer

Before you refit the line strainer check the condition of the fibre washer or rubber seal and replace it if it looks damaged - you can buy washers and seals from DIY stores and plumber's merchants, often in packs of mixed sizes if you are not sure of the correct size to buy (take the old one with you when you buy if you are not sure of the size).

If there is no washer or seal then wrap a little PTFE tape around the thread of the nut (again available from DIY store/plumbers' merchants), about four or five full turns of tape around the thread should be plenty to help make a seal.

Make sure you wrap the tape in the direction of the turn of the thread up the nut towards the hexagon head otherwise the tape will undo as you tighten the nut.

Put the mesh back into the housing, making sure that it fits in correctly if there is a specific mounting position.

Refit the nut and using just your fingers tighten it slowly, taking care to make sure that the thread is engaged properly before you wind it in fully with a spanner.

Once the nut is tight go back to the tap and turn it off, then go to the stop valve and open it up slowly, watching the line strainer for leaks as you do so. Once the stopvalve is fully open return to the tap and open it slowly until water begins to flow again, then turn it off.

Return once more to the line strainer and check for leaks from the nut. If there is a small leak or weep then very gently tighten the nut a little more, being careful not to overtighten it and strip the thread.

Finally, make a note in your diary to clean it again in no more than a year's time!
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