The best bleed keys, compared.
Top pick: Heatlab dual-size radiator key – Highest score at 96: a 7.5 cm 17-7 stainless lever with imperial and metric ends, 4.8 from 1,393 ratings, at about £6.99. Best value: Nartel brass radiator keys, pack of 2 – About £3.49 with 4.5 from 1,295 ratings. Lowest shelf price with a large rating file. Socket size is not stated. Updated 22.10.2026.
A bleed key turns the square bleed screw on a UK hot-water radiator or heated towel rail so trapped air can escape. You buy one when the top of a radiator stays cold, the panel gurgles, or a towel rail only heats at the bottom. British Gas, the Energy Saving Trust and Gas Safe treat a single bleed as DIY, with the heating off and the radiator cool. Most modern screws are described as 5 mm square. Older imperial pins, some towel rails and lockshield spindles are different parts, so a title that says the key fits all is a claim to test. How to vent a cool panel is in [how to bleed a radiator](/hub/diy-supplies/bleed-key/sub/bleed-key-how-to-bleed). Quality is a snug socket, enough leverage to turn a stiff pin without pliers, and a spare. An 8 mm-only key is a different pin. That fit question is covered under [imperial or metric bleed keys](/hub/diy-supplies/bleed-key/sub/bleed-key-imperial-or-metric). A short brass clock key fits a tight alcove and digs into fingers. A longer stainless lever turns stiff screws and is clumsy where the valve is buried. Do not add pliers to a soft key.
A bleed key turns the square bleed screw on a UK hot-water radiator or heated towel rail so trapped air can escape.
42 products checked · 58 hrs invested · +21,400 readers
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Personal buying guide
Question 1 of 2
How does the bleed screw behave?
The Heatlab dual-size key at £6.99 is one 17-7 stainless lever, 7.5 cm long and 15 g, with imperial and metric ends, and 4.8 from 1,393 amazon.co.uk ratings. Reviewers call it sturdier than a small brass clock key, say the longer handle turns tight bleed nipples, and say both sizes helped in houses with older and newer radiators after a short brass key had failed. It is one key, not a pair, and a pouch shows up in reviews rather than in the technical block. The title says ultimate, which some reviewers treat as stronger than the tool, and one note says the metric end is not a perfect fit on every radiator. There is no repeated snap in the sampled reviews, and reviewers used it on stiff pins that were still square, not on a screw that was already round. It is the top pick here for a stiff or mixed-age house, at about twice the price of a brass pair, and it is clumsy where the valve is buried in a very tight gap.
Pros
Cons
Best for: You have a stiff bleed screw, or older and newer radiators in the same house, and the pin is still square.
Less suitable: One easy 5 mm screw in a cramped alcove, or a pin that is already rounded.
Specifications
Common questions
What is different about this key?
The listing is one stainless piece with imperial and metric ends and a 7.5 cm handle, not a pair of small brass wings.
What do the reviews repeat?
Buyers say it turned stiff screws and fitted mixed older and newer radiators after a short brass key had failed.
The Heatlab PlumbShark, model 1111002, is one 17-7 stainless multi-tool at £12.99, with 4.7 from 510 amazon.co.uk ratings. The listing leads with a radiator bleed key and also names a meter-box key, a lockshield key, a drain-off spanner, an isolation-valve tool, and a gas-meter test nipple. Reviewers say the one piece covers bleed, lockshield, and meter box, that it feels solid, and that it lives on a keyring or van keys, with an easier bleed than a short key on stiff pins. The meter-box end is too short for some, the carabiner is large, and the tool is bulky where the bleed screw is cramped. No repeated snap is in the sampled reviews. The gas-meter test nipple is a gas fitting, not a household bleed step, and work on a gas fitting is not a DIY extra. At £12.99 it costs more than the dual-size Heatlab lever, and you are paying for nine other tips you may never use on a radiator.
Pros
Cons
Best for: You already do meter-box and lockshield jobs and you want the bleed socket on the same stainless tool.
Less suitable: A first bleed key for one tight radiator, or anyone who might treat the gas-test end as DIY.
Specifications
Common questions
Is this only a bleed key?
No. The listing also includes a meter-box key, lockshield key, drain-off spanner, isolation valve tool and a gas-meter test nipple.
What do reviews criticise?
The meter-box end is too short for some, the carabiner is large, and the tool is bulky in a tight bleed-screw gap.
The Equip247uk pair, model EQCLKRKEYX2, is two brass clock keys at £3.95, listed at 10 g and 1 × 5 × 0.5 cm, with 4.7 from 295 amazon.co.uk ratings. Reviewers call them solid, easy to hold, and useful because hanging holes take a string or a carabiner. The listing says most standard radiator valve sizes and does not give a millimetre figure. More than one buyer found the socket loose, one by about 0.5–1 mm, and one says the female side only covers the pin by a few millimetres. The ears are also called a bit small. That short engagement is the limit: a key that barely grips can round a stiff screw even when the star line is high. It is a light spare pair if the pin is easy, and a poor bet once a previous key has already started to spin.
Pros
Cons
Best for: You want a second brass pair on a keyring for radiators that already turn with a light key.
Less suitable: A stiff or older pin, or any screw that already feels rounded.
Specifications
Common questions
Is the socket a stated 5 mm?
No. The listing says most standard radiator valve sizes and does not give a millimetre size.
Do reviews mention the fit?
Yes. More than one review says the socket feels loose, and one says the female side is only a few millimetres deep.
The RDXMAX set at £5.99 is a silver kit listed at 28 g and 7.2 × 2.4 × 1 cm, with 4.7 from 46 amazon.co.uk ratings. The title names a bleed key, a spanner, and a lockshield valve key. A Vine review describes two pieces, a small bleed key and a longer bleed handle, and says both fitted older radiator bleed valves, with the long handle used on stiff ones. That same review calls the lockshield claim misleading. Other notes say the set feels cheap and that the small wings are hard to grip. The metal is not one material in the file: a review separates a zinc-alloy bleed key from a stainless handle. Forty-six ratings are a short file next to pairs with more than a thousand, so the 4.7 does not show how the set behaves after a winter of stiff screws. Keep it for the longer bleed handle if the reviews match your older valves, and do not buy it because the title says lockshield.
Pros
Cons
Best for: You want a longer bleed handle for older radiator pins and you can ignore the lockshield wording.
Less suitable: You need a proven lockshield tool, or a review file larger than a few dozen.
Specifications
Common questions
Does the set include a lockshield key?
The title says so. A Vine review says the set is useful for bleeding and that the lockshield claim is misleading.
What did reviewers actually use?
They describe two bleed keys, and say both fitted older radiator bleed valves, with the long handle used on stiff ones.
The Mellbree set at £5.99 is solid brass, listed at 30 g, with a compact hex bleed key and a dedicated towel-radiator key, and 4.6 from 274 amazon.co.uk ratings. The package-quantity field says 3, while the bullets name those two tools, so a third piece is not described. Reviewers call the brass solid, say the tommy-bar style gives leverage, and say a different key shape helped hard-to-reach valves, including after a previous key had snapped. One buyer found them a bit small. No repeated break of this set is in the sampled reviews. The listing also says metric and imperial, which is a claim, not a printed millimetre for each end. It is the towel-rail set in this table that has a review file, and it is still a small brass tool if your hands want a long lever.
Pros
Cons
Best for: You have a panel radiator and a towel rail and you want both tips from a set people have reviewed.
Less suitable: You only have easy 5 mm panel screws, or you need a 7.5 cm stainless lever.
Specifications
Common questions
Does this set cover a towel rail?
The listing says it includes a compact hex bleed key and a dedicated key for towel radiators.
What do reviews say about size?
Buyers call them solid. One found them a bit small. No repeated break of this set is in the sampled reviews.
The Nartel pair at £3.49 is two solid brass clock keys, model 42599, listed at 20 g and 5 × 9 × 0.3 cm, with 4.5 from 1,295 amazon.co.uk ratings. Reviewers say the keys do the bleed, that the wider wings give purchase on the screw, and that a hanging hole lets a spare stay on a radiator or a keyring. The listing describes a square opening for most radiator systems and does not state 5 mm, so you still have to seat it on your own pin. Some buyers found the socket loose and the finish rough, and one review says a key snapped after a short time. A loose square can round the bleed screw if you keep turning once it starts to spin. It is the best value row here because it is the lowest shelf price with a four-figure rating count, not because a millimetre size is printed.
Pros
Cons
Best for: You want a cheap spare pair for a modern square pin and you will check the seat before you lean on it.
Less suitable: You need a printed 5 mm size, or the last brass key already spun on a stiff screw.
Specifications
Common questions
How many keys are in the pack?
The listing includes two solid brass radiator keys.
What size is the socket?
The listing says a square opening for most radiator systems. It does not state 5 mm.
What do buyers complain about?
Some reviews call the socket loose or the finish rough. One review says a key snapped after a short time.
The Goodility pair, model 5mm BRK 2024, is two brass keys sold as 5 mm at £3.99, listed at 20 g and 3.4 × 3 × 0.5 cm, with 4.5 from 234 amazon.co.uk ratings. Buyers who had no trouble say the key fitted a standard radiator and did a seasonal bleed, and the positive reviews mention a solid brass feel. Other reviews call the metal soft and a bit flimsy, say the key slips off the valve, and say the square smooths until it spins and will not open the screw. The same file says the metal bends when you turn a stiff pin. A stated 5 mm size is what you are paying for here, and the soft-square reviews are the reason not to lean on it once the screw resists. At the same £3.99 as the QUERGO pair, the difference is that QUERGO also prints a 12 mm socket depth and this listing does not.
Pros
Cons
Best for: You want the words 5 mm on a cheap pair for an easy modern bleed screw.
Less suitable: A pin that is already stiff, or a house where a previous brass key has bent.
Specifications
Common questions
Does the listing name the size?
Yes. The title and bullets say a 5 mm radiator bleed key for UK valves.
What failures show up in reviews?
Some buyers say the metal is soft, the square smooths off, the key slips, or it bends on a stiff screw.
The QUERGO pair at £3.99 is two brass keys with a stated 5 mm square socket, 12 mm deep and 9 mm across the outside, listed at 20 g, with 4.4 from 455 amazon.co.uk ratings. Reviewers say the keys bleed their radiators and that the short body reaches a screw tucked into a corner. The same file says the wings or T-bar are too short to grip, that larger fingers struggle, and that the handle jabs the skin. Comfort, not a run of broken keys, is the repeated complaint. On a stubborn screw the short wings give poor leverage unless you add a grip, and adding pliers is how a soft square gets rounded. The stated depth is the useful part of this listing: you can see 12 mm of socket before you buy, which several other brass pairs in this table never print.
Pros
Cons
Best for: You have a standard 5 mm pin in a tight alcove and you can turn it without a long lever.
Less suitable: A stiff screw, large hands, or a gap where you need a longer handle rather than a short one.
Specifications
Common questions
What socket size does QUERGO state?
5 mm square, 12 mm deep, outside diameter 9 mm.
Why do some buyers dislike the handle?
Reviews say the wings are short, so the key is hard to grip, though the short body helps in a tight gap.
The Minimprover set at £4.94 is a zinc-alloy kit in a case, listed at 150 g with a package of 19.9 × 11.7 × 3.2 cm, and 4.3 from 327 amazon.co.uk ratings. The bleed pieces are two 5 mm square radiator keys, sold with a 7-in-1 utility key, a 5 mm cabinet key, a 6 mm cabinet key, and a chain. Reviewers call it a handy household set, say the case keeps the keys together, and say the 5 mm keys did the bleed. Quality is described as reasonable rather than heavy, and one buyer only needed the radiator keys. One review says it broke on first use, with no second repeated break in the first 50 reviews. One reviewer also mentions using a 5 mm and a 7 mm key, so the extra ends are for cupboards and meters, not a second radiator size. You are paying £4.94 for a box of jobs, and the radiator part is still a pair of 5 mm squares.
Pros
Cons
Best for: You want 5 mm bleed keys and a meter-box key in one case.
Less suitable: You only need one radiator key, or you need a long lever for a stiff screw.
Specifications
Common questions
Which piece bleeds a radiator?
The listing includes two 5 mm square radiator keys, plus a 7-in-1 utility key and 5 mm and 6 mm cabinet keys.
Did any review report a break?
One review says it broke on first use. Most of the sampled reviews say the set did the job.
This unbranded pair is listed at £4.49 as two 8 mm square metal keys, 20 g, with a fixed square head. The title says two pieces and the package-quantity field says 1, so the box count is not clean in the file. The listing also mentions taps and outdoor gas taps, which is a different job from a radiator bleed screw. Typical modern bleed screws are described as 5 mm square, and this saved listing does not show the 8 mm socket seated on a 5 mm pin. An 8 mm opening is larger, not a closer fit for a small older pin. There is no customer-review line, so there is no star rating and no buyer account of whether the square holds. At £4.49 it sits in the entry band without the proof the cheaper 5 mm pairs at least attempt.
Pros
Cons
Best for: You have already measured an 8 mm square pin and you only need that size.
Less suitable: A modern 5 mm radiator screw, or any pin you have not measured.
Specifications
Common questions
Is 8 mm the usual radiator bleed size?
The listing is 8 mm. Typical modern bleed screws are described elsewhere as 5 mm. This saved listing does not show a fit on a 5 mm pin.
Is there a star rating?
No customer-review line is in the saved listing, so there is no star rating.
The Yabgkgagnan 3-pack at £5.29 lists a square vent key, a hex radiator key, and a towel-rail valve key, with brass claimed in the bullets and a listed weight of 10 g in a 10 × 10 × 1 cm pack. The technical included-components field says NO, and the model field says NO, so the box contents are not confirmed beyond the bullets. The listing talks about imperial and metric panel radiators and towel rails, and it does not print a millimetre size for any socket. There is no customer-review line, so nobody in this file has said the towel-rail tip seated. A named towel-rail key is the reason the pack is in the table, and the missing rating is the reason it does not carry a pick. Mellbree, at £5.99, names a towel-rail key and has 274 ratings; this pack does not.
Pros
Cons
Best for: You are comparing towel-rail claims on the listing page and you will not buy on an empty review line.
Less suitable: You want buyer comments on the towel-rail tip before you pay.
Specifications
Common questions
What is in the pack?
The bullets list a square vent key, a hex radiator key and a towel-rail valve key. The technical included-components field says NO.
Is there a star rating?
No. The saved listing has no customer-review line.
The GZYiLingMY 5-pack at £6.99 lists five metal radiator keys, model zxdqs1, at 20 g and 13 × 3.5 × 1.5 cm, each with a hanging hole. The material field says metal and does not say brass or steel. The listing claims a square fit for standard and corner valves and does not state a millimetre size. There is no customer-review line, so the file has no stars and no comment on whether the square seats. Five keys sound useful because bleed keys get lost, and Nartel already sells two brass keys for £3.49 with 1,295 ratings. Paying £6.99 for five unmeasured, unreviewed keys is a spare-drawer idea only if you already know the pin and you accept that nobody in this capture has reported a fit. The colour field reads gold silver, which does not tell you the metal.
Pros
Cons
Best for: You already know your pin size and you only want several identical spares to leave around the house.
Less suitable: A first key, a stiff screw, or any purchase that depends on reviews.
Specifications
Common questions
How many keys are included?
Five. The listing says each has a hanging hole.
Is the metal brass?
The technical block says metal. It does not say brass or steel.
Shelf prices and star lines are the amazon.co.uk figures stored for these twelve listings on 19 October 2026. Review themes are the notes already stored for those ASINs. This is not a laboratory test. A title that says universal, lockshield or towel rail is not scored as proof. A listing with no customer-review line scores 0. The highest score is the top pick. Best value is the lowest shelf price among keys with more than 50 ratings. It does not also take the top score, because that pair does not state a millimetre size and some buyers found the socket loose.
Amazon evidence
30%Star rating on amazon.co.uk, then the review count. A 4.8 from 1,393 ratings carries this block. A 4.7 from 46 ratings takes less of it. No review line takes none of it.
Listing fit
25%A stated 5 mm socket, a stated second size, a socket depth, or a named towel-rail tip. An 8 mm-only key, a size that is not stated, and a gas-meter test nipple treated as a household extra are deductions.
Review outcome
25%Themes about a key that seated and turned a stiff pin. A loose or shallow socket, a square that smooths, a wing that will not grip, and a lockshield claim a reviewer calls misleading are deductions. No review text cannot fill this block.
Value
20%Stored GBP price against a stated size and a review count above about 50. About £3.49 for a brass pair with 1,295 ratings takes this block. About £6.99 for five keys with no reviews does not, and that row is already at 0 because the review line is missing.
Buy the socket before a title that says the key fits all. A bleed key has to match the pin on your radiator or towel rail, then give enough leverage without pliers. Most modern screws are described as 5 mm square. Older pins, some towel rails and lockshield spindles are different parts. Brass pairs are the cheap spare and can bend. A longer 17-7 stainless lever costs more and is what reviewers pick after a short brass key has failed.
A bleed key turns the square bleed screw on a UK hot-water radiator or heated towel rail so trapped air can escape. You look for one when the top of a radiator stays cold, the panel gurgles, or a towel rail only heats at the bottom. British Gas, the Energy Saving Trust and Gas Safe Register treat a single bleed as DIY, with the heating off and the radiator cool. Quality is a snug socket, enough leverage to turn a stiff pin without pliers, and a spare.
British Gas, the Energy Saving Trust and Gas Safe Register treat a single bleed as DIY with the heating off and the radiator cool. Open the screw a quarter to half a turn, and not more than about two turns, and do not remove it. Close it when the hiss stops and water appears.
Most modern screws are described as 5 mm square. An 8 mm-only key is a different pin. Older imperial pins, some towel rails and lockshield spindles are different parts. A lockshield line on a title is a claim. One RDXMAX review calls that claim misleading.
A short brass key can bend or lose its corners. Adding pliers to get a grip is how a soft square gets rounded. If the pin is stiff and still square, use a longer lever. If it is already round, a new key will not restore it.
Look at the bleed screw before you trust a title. Wonkee Donkee describes the usual modern head as 5 mm square, often with a screwdriver slot as well. An 8 mm-only key is a different pin. In this set the unbranded pair at about £4.49 is 8 mm, and the saved listing does not show that socket seated on a 5 mm screw. If a new 5 mm key spins or will not enter an older radiator, try a clock-key size. Viessmann UK points at sizes about 8 to 12 on imperial-era radiators.
A short brass clock key fits a tight alcove and digs into fingers. A longer stainless lever turns stiff screws and is clumsy where the valve is buried. Do not add pliers to a soft key. That is how a square gets rounded. Brass pairs are the cheap spare. Reviews of the cheaper brass listings include a loose socket, a square that smooths, and a key that bends on a stiff screw. The 17-7 stainless levers cost more. Reviewers pick them after a short brass key has failed.
Three typical situations, each with a recommendation from this comparison.
You have modern panels and you want a stated 5 mm socket. The QUERGO pair is about £3.99, with a 5 mm square listed as 12 mm deep and 4.4 from 455 ratings. The short wings are the complaint: they are hard to grip and poor on a stiff screw. It is the row that prints both the size and the depth.
The house mixes older and newer radiators, or a short brass key has already failed on a pin that is still square. The Heatlab dual-size key is the top pick at about £6.99: a 7.5 cm 17-7 stainless lever with imperial and metric ends, and 4.8 from 1,393 ratings. One review says the metric end is not a perfect fit on every radiator.
You want two brass keys to leave on a radiator or a keyring, and you will check the seat before you lean on it. The Nartel pair is best value at about £3.49, with 4.5 from 1,295 ratings. The socket size is not stated. Some buyers found the square loose, and one review says a key snapped.
The top pick is the Heatlab dual-size radiator key at about £6.99. It scores 96, the highest here: one 17-7 stainless lever, 7.5 cm long, with imperial and metric ends, and 4.8 from 1,393 ratings. Reviewers used it on stiff pins that were still square. One note says the metric end is not a perfect fit on every radiator. Best value is the Nartel brass pair at about £3.49, with 4.5 from 1,295 ratings. It is the lowest shelf price with a four-figure rating count. The socket size is not stated, and some buyers found the square loose.
Heatlab dual-size radiator key
Highest score at 96: a 7.5 cm 17-7 stainless lever with imperial and metric ends, 4.8 from 1,393 ratings, at about £6.99.
Nartel brass radiator keys, pack of 2
About £3.49 with 4.5 from 1,295 ratings. Lowest shelf price with a large rating file. Socket size is not stated.
Editorial
Peter F. is the editor for DIY & tools at productscompared.co.uk. Comparisons in this category are checked against amazon.co.uk listings, review evidence and public UK sources.
Guides on what to look for, how to use a product, and common mistakes.
Public UK sources from the digest, and the amazon.co.uk shelf prices stored for 19 October 2026. Page updated 22.10.2026.
This page contains affiliate links to amazon.co.uk (tag pcuk26-21). If you buy through them, we may earn a commission at no extra cost to you. Prices, stars and review counts are the amazon.co.uk figures already stored for this set. This is not a laboratory test.
