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Can A Hot Water Bottle Burst? 6 Rules to Be Safe

Updated: Jan 21, 2023


can a hot water bottle burst icon

We've seen this question come up many times on the web: can hot water bottles burst or explode? How likely is this? In which conditions?


We crafted an article outlining basic rules to adhere to prevent your hot water bottle from bursting.


Although unlikely and rare, hot water bottles can burst or explode. These incidents leading to direct contact with hot water can result in severe burns and injuries.


Again, don't be scared, hot water bottles are there to keep you warm and comfort you, not to send you to the burns unit! Make sure you follow the easy steps outlined below.


We explain how to best fill and use hot water bottles to avoid accidents. Follow these and your experience will be as warm and cosy as it should be!


two hot water bottles in bed

Can hot water bottles burst?

Hot water bottles burst only on very rare occasions. To prevent the unlikely event of your hot water bottle bursting, make sure you only fill it up to only two-thirds of its maximum capacity, gently push the air out of the bottle before sealing it, and do not sit, stand, or lay on it. Make sure your hot water bottle hasn't expired and adheres to the British Standard (BS 1970:2012). Check for signs of wear and tear before each use.


6 important rules to prevent hot water bottles to burst

rules to prevent hot water bottle burst

1. Check your bottle adheres to the British Standards (1970:2012)

This is the first important step you should take before using your hot water bottle: checking it adheres to the British Safety Standards (labelled BS 1970:2012 on your bottle).


This standard is important as it guarantees your hot water bottle is safe for use, provided you use it within the guidelines (all of which as cited in the points below).


Most importantly, hot water bottles produced within this British Standard have a guaranteed resistance and are very unlikely to burst if you fill, use, and store your hot water bottle correctly.


2. Check your hot water bottle expiry date

Yes people, hot water bottles have an expiry date, just like food and condoms! You will find a stamp on your hot water bottle, called a daisy wheel. This daisy wheel indicates when your hot water bottle was manufactured (see how to read the wheel below).


daisy wheel explanation

In this case, the hot water bottle was manufactured in the first week of January 2022.


Once you've noted the date of manufacture, check how long your hot water bottle is safe for use by referring to the user's manual. You have probably thrown it away: so let us guide you further. Hot water bottles should be replaced every 2 years approximately.


Some brands such as Fashy manufacture bottles which can last up to 5 years. In case of doubt, play it safe: if your hot water bottle is more than 2 years old, replace it and purchase a new one. Take a picture of the instructions this time!


If you use a hot water bottle which has expired, the material may be damaged. Damaged material equals a higher risk of your item bursting. Let's avoid this!


Rule

Check your hot water bottle expiry date if you haven't used it for a while, and cross-check with the recommended lifespan given by your hot water bottle manufacturer.


3. Check hot water bottles for leaks before using

Depending on how well and how much you've been using your hot water bottle, it is normal that the material resistance decreases and tears appear over time. Make sure you check your hot water bottle is safe before each use.


Fill it with cold water and give it a gentle squeeze to check for leaks. You can also fill it with air and push it into a bucket of water to check for bubbles (if you see bubbles, your bottle has holes). If the test is successful, reuse that water for your kettle and your hot water bottle (let's save water people!).


If you see even minor leaks while performing these tests, stop using the hot water bottle immediately and buy a new one. Even a small tear may turn into a larger one and lead your hot water bottle to burst. This in turn may lead to severe burn injuries. Let's avoid that!


Rule

Check your hot water bottle doesn't have tears or holes before each use. Perform a thorough test with cold water!


4. Do not fill your hot water bottle at maximum capacity

Another important step to preventing your hot water bottle from bursting. By filling it to the top and sealing it with the stopper, the hot water bottle will face too much pressure from the inside. To illustrate, think of what would happen if you filled a balloon with water and stepped on it. Boom.


Even though your hot water bottle is far more resistant than a balloon, sufficient pressure from the inside, coupled with hot water can lead the material to tear and the bottle to burst.


While some websites and manufacturers advise you to fill it up to three quarters, we follow Fashy's (this is not an ad, we just trust them since they've been manufacturing hot water bottles since 1948) and the British Standard recommendation to fill it up to two thirds, which is less than three quarters. Better safe than sorry!


Rule

Only fill your hot water bottle two-thirds of its maximum capacity.


full hot water bottle

hot water bottle filled two-thirds

5. Push the air out as you fill your hot water bottle

This rule is linked to the previous one. If you leave air in your hot water bottle after having filled it and sealed it, you will face the same "balloon effect". Too much air on the inside can constitute too much pressure on your hot water bottle.


If your hot water bottle has too much air and you accidentally sit on it, step on it or lay on it (in bed while sleeping with your hot water bottle for example), it may burst. Boom again.


Rule

Once you've filled your hot water bottle two-thirds, gently lay it on a flat surface holding it by the neck, and slowly push the air out with the palm of your hand. Once sealed, your bottle should be flexible and bendable, not be bloated like a balloon.


hot water bottle being bent

6. Do not use boiling water

Hot water bottles have very resistant material (rubber, PVC, or silicone in most cases). That being said, the material is designed to withstand hot water of a maximum of 80 degrees Celsius over a long period.


Manufacturers and retailers explicitly instruct us, consumers, not to use boiling water (100 degrees Celsius) for hot water bottles, as this may damage the material and lead to tears over an extended period. Your hot water bottle will hence be more prone to bursts.


Rule

Only fill your hot water bottle with water of approximately 80 degrees Celsius. Once you've boiled water in your kettle, let it cool for about 10 minutes to reach optimal temperature.


Final thoughts

Hot water bottles can burst on very rare occasions. Filling and using your hot water bottle correctly will prevent this unlikely event.


hot water bottles in bed sheets

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