Knowing how to winterise your boat is far more than just another seasonal chore; it’s about protecting one of your most valuable assets. Here in the UK, it only takes one unexpected cold snap for disaster to strike. A single freeze can lead to a cracked engine block or burst pipes, landing you with a repair bill running into the thousands.
This guide will walk you through everything, from the engine and plumbing to the heating systems and exterior care, making sure your narrowboat or canal barge is ready to go the moment the boating season returns.
For quotes and bookings, call or email us here.
Why Winterising Your Boat Is So Crucial in the UK
Getting your boat ready for winter is easily one of the most critical maintenance jobs you’ll do all year. The main goal is simple: protect your vessel from the punishing effects of freezing temperatures, relentless damp, and just sitting idle for months on end.
When water freezes, it expands by about 9%. That might not sound like much, but it exerts an incredible force—more than enough to fracture heavy-duty engine components, split plumbing pipes, and wreck expensive pumps.
I’ve seen it happen time and again. Forgetting even one small detail, like a sea strainer or a deck wash pump, can lead to a costly and deeply frustrating start to the next season. Think of proper winterisation as a cheap insurance policy that safeguards your investment, keeping your narrowboat or canal barge in top nick.
It’s Not Just About Preventing Freeze Damage
While protecting your boat from turning into a solid block of ice is the top priority, a thorough winterisation process has plenty of other perks. It’s the perfect time to tackle the annual maintenance that often gets pushed aside during the busy boating season.
A good winter routine includes:
- Engine Health: Change the oil and filters. This gets rid of corrosive gunk that can sit and eat away at your engine’s internal parts over the winter.
- Fuel System Integrity: Always add a fuel stabiliser. It stops varnish and gum from building up, which keeps your fuel lines and carburettors clear and ready for spring.
- Mould and Mildew Prevention: A deep clean paired with good ventilation is your best defence against damp. It stops mould from taking hold and turning your cabin into an unpleasant, unhealthy space.
- Pest Control: Get rid of every last crumb of food and block up any potential entry points. It’s the only way to stop rodents and other pests from deciding your boat is their new winter home.
This proactive approach is especially important for those of us on the UK’s inland waterways. The government’s own mid-year report on waterway management points to a big seasonal shift, with a huge spike in maintenance jobs during the quieter autumn and winter months. You can read more about this trend in the full 2025 mid-year waterways report.
By putting in the effort to winterize your boat properly, you’re doing more than just dodging repair bills. You’re actively extending the life of your vessel and making sure it’s reliable and safe for many years to come.
Looking After Your Boat’s Engine and Fuel System
Your boat’s engine is its heart, and when it comes to laying up for winter, it absolutely has to be your top priority. Honestly, neglecting the engine and fuel system is the fastest way to guarantee yourself a frustrating and expensive start to the next boating season. This isn’t just about stopping things from freezing; it’s about protecting all those internal components from corrosion and making sure your fuel doesn’t turn into sludge.
The steps below are a solid path for winterising the inboard engines you typically find on UK narrowboats. While your engine’s own manual should always be the final word, these are the bedrock practices of good winter engine care that I’ve seen work time and time again.
Start with an Oil and Filter Change
The very first job on the list should be changing the engine oil and filter. No excuses. Over a season of running, your oil gets loaded with all sorts of nasty stuff – acids, carbon, and water. Leaving that corrosive cocktail stewing in your engine all winter is just asking for internal damage.
Always run the engine for a few minutes before you drain the oil. This simple step warms it up, making it thinner and allowing it to flow out more easily, taking more of the gunk with it. Once it’s drained, spin on a new oil filter and refill with fresh oil that meets your manufacturer’s spec. This leaves your engine’s internals coated in clean, protective oil, ready to fight off moisture and corrosion during the long, cold layup.
A classic mistake is putting off the oil change until spring. By then, the damage from corrosive by-products and moisture sitting in the engine for months has already happened. Always change the oil before winter storage, not after.
Tackling the Fuel System
Modern fuel, especially diesel, can cause major headaches if you just leave it in the tank all winter. It can degrade, suck in water, and form gummy deposits that will happily clog up your fuel lines and filters come springtime.
How you approach this depends a little on what your tank is made of:
- Metal Tanks: The best practice is to fill the tank to about 95% full. This leaves just enough room for the fuel to expand if the temperature changes, but massively reduces the amount of air inside. Less air means less chance for condensation to form on the tank walls.
- Plastic Tanks: Advice can vary here, but a lot of boaters prefer to leave them almost empty. Plastic is much less prone to condensation than metal. If in doubt, see what your boat’s manufacturer suggests.
No matter the fill level, adding a quality fuel stabiliser is non-negotiable. After pouring in the right amount for your tank size, run the engine for a good 10-15 minutes. This is a critical step – it pulls the treated fuel right through the entire system, from the lines and pumps to the injectors, ensuring every last component is protected.
Flushing and Filling the Cooling System
For any engine that uses raw water for cooling, getting every last drop of that water out is absolutely essential. A frozen and cracked engine block or manifold is a season-ending disaster. Even engines with a ‘sealed’ closed-cooling system have a raw water side that needs the same attention.
The goal is to completely replace the raw water with a non-toxic, propylene glycol-based marine antifreeze. Whatever you do, never use ethylene glycol (the stuff you put in your car) as it’s incredibly toxic to fish and other aquatic life.
The job usually involves closing the raw water seacock and using a bucket or a special flushing kit to suck the antifreeze mixture into the system. You keep going until you see the coloured antifreeze coming out of the exhaust. That’s your signal that the entire circuit is filled and protected from freezing.
Final Checks and Preventive Steps
With the big jobs done, a few final checks will see your engine properly put to bed for the winter.
First up, have a good look at all the belts and hoses. You’re looking for any cracks, shiny spots, or hoses that feel brittle and hard. It’s far better to find a failing hose now in the calm of your mooring than to have it burst on your first trip out next year.
If you have a petrol engine, using fogging oil gives you a brilliant extra layer of protection. This stuff is sprayed directly into the carburettor or air intake while the engine is running. It creates a fine mist that coats the cylinders, pistons, and valves with a protective film, stopping rust from forming on these critical surfaces.
Finally, check all the associated connections. This is the perfect time to give nearby systems a once-over, including things like your gas lines. Making sure you have a properly installed and undamaged LPG gas hose is a simple safety check that brings real peace of mind before you lock up. Once you’re happy, disconnect the battery terminals to stop it from slowly going flat, and if you can, store the battery somewhere cool and dry on a trickle charger.
Securing Your Plumbing from Freezing Temperatures
With the engine sorted, your attention should now turn to the plumbing. A burst pipe on a boat is far more than a simple inconvenience; it’s a potential disaster that leads to widespread water damage, rot, and stubborn mould. The entire goal here is to get every last drop of water out and replace it with non-toxic antifreeze, leaving nothing behind to freeze, expand, and crack your pipework.
This process touches everything connected to your water system: freshwater tanks, pumps, taps, toilets, and showers. It might feel like a long list of jobs, but a methodical approach is your best defence against a very expensive and messy surprise come springtime. You need to walk away confident that every part of the system is fully protected.
Draining the Entire System
First things first, you need to get as much water out as you possibly can. Kick things off by completely emptying your freshwater tank. Next, open every single tap on the boat—both hot and cold—at the kitchen sink, the bathroom basin, and in any showers. Let the water pump run until it’s just sputtering air, which tells you the main lines are clear.
And don’t forget the hot water heater or calorifier. These things hold a surprising amount of water and have their own drain plugs for a reason. Make sure you drain it completely. Leaving water in the calorifier is a classic, costly mistake, as a hard freeze can easily rupture the tank.
Blowing Out the Lines
Even after a thorough drain, pockets of water will inevitably get trapped in low points of your pipework, in U-bends, and inside the pumps. Gravity alone just won’t cut it. This is where a bit of compressed air becomes your most valuable tool.
Using a low-pressure air compressor (around 20-30 PSI is more than enough), you can systematically blow out each water line. You’ll need a special adaptor that screws into your water intake fitting. Work your way through the boat, opening one tap at a time until only a fine mist of air is coming out. This step is absolutely crucial for clearing out every last bit of residual water.
A Quick Tip: It’s not just the main pipes you need to worry about. Pay close attention to often-forgotten spots like deck wash pumps, shower sump pumps, and sea strainers. Each one can hold water and is a prime candidate for freeze damage if you overlook it.
The principles of protecting your plumbing are much the same as for your engine—it’s all about proactive, thorough maintenance to prevent winter damage.
This visual just reinforces the idea that a multi-step, systematic approach is the only way to guarantee comprehensive winter protection.
Circulating Marine Antifreeze
With the system now empty, it’s time to introduce a non-toxic, marine-grade propylene glycol antifreeze. Under no circumstances should you use automotive (ethylene glycol) antifreeze. It is extremely toxic and causes serious harm to aquatic life if it ever gets discharged.
You’ve got a couple of options for getting the antifreeze into the system:
- Pour it directly into your empty freshwater tank and use the boat’s own pump to circulate it through the lines.
- Disconnect the inlet side of your water pump and use a short bit of hose to draw the antifreeze straight from the bottle. This is often the quicker method.
Once you’re set up, turn on the pump and go back to each tap. Open the hot and cold sides one by one until you see the coloured antifreeze flowing out. Do this for the shower, the toilet flush, and any other water outlet on board. When you see that pink or blue liquid, you know the entire line is filled and protected.
As a final step, pour a little extra antifreeze down each drain to protect the P-traps and any grey water tanks. For a more detailed look at these components, our guide to boat plumbing systems offers some great information.
To help you keep track, here’s a straightforward checklist for your plumbing winterization tasks.
Winterization Checklist for Plumbing Systems
| Component | Action Required | Antifreeze Needed? |
|---|---|---|
| Freshwater Tank | Drain completely until empty. | No (unless using it to circulate antifreeze) |
| Water Pump | Run until it sputters air, then blow out with compressed air. | Yes – run until antifreeze flows through. |
| Hot Water Heater | Isolate and drain completely using the dedicated drain plug. | No – bypass this component. |
| Taps (Galley/Heads) | Open hot & cold sides, blow out, then run antifreeze through. | Yes – until coloured liquid appears. |
| Shower Head & Hose | Drain hose completely, blow out, then run antifreeze through. | Yes – until coloured liquid appears. |
| Toilet (Manual/Electric) | Pump system dry, then flush with antifreeze. | Yes – pump through until bowl fills with antifreeze. |
| Drains & P-Traps | Pour a small amount of antifreeze directly down each drain. | Yes – approx. 250ml per drain. |
| Ancillary Pumps | Disconnect, drain, and blow out any deck wash or sump pumps. | Yes – run antifreeze through or manually fill pump body. |
Following this checklist methodically ensures you won’t miss a single part of your boat’s water system, giving you peace of mind throughout the winter.
Servicing Your Marine Heating System for Winter
There’s nothing quite like having a reliable heater when you pop down to the boat on a cold winter’s day. It’s the difference between a pleasant visit and a miserable one, and it’s absolutely essential for getting the new season off to a comfortable start. If you neglect it now, you can almost guarantee it’ll fail just when you need it most.
Whether your boat has a modern diesel heater or a classic solid fuel stove, giving it a pre-winter service is a non-negotiable part of winterising your boat properly. This is about more than just staying warm; it’s a critical safety issue. A poorly maintained heater isn’t just inefficient—it can be a serious hazard.
Keeping Your Diesel Heater in Top Condition
Modern diesel heaters from brands like Webasto and Eberspacher are brilliant bits of kit, but they won’t look after themselves. They need a bit of regular attention to work reliably. More often than not, the culprit behind a heater that won’t fire up on a frosty morning is something simple, like a clogged fuel line or a sooty burner.
Here’s what should be on your pre-winter checklist:
- Check the Fuel Filter: This little component is your first line of defence against debris. Take a close look at the small inline fuel filter. If it looks clogged up, clean it or, better yet, just replace it. A restricted fuel flow will starve the heater and cause it to cut out.
- Inspect the Exhaust System: Go over the entire length of the exhaust pipe with a fine-tooth comb. You’re looking for any signs of corrosion, cracks, or loose fittings. A leak here can release deadly carbon monoxide into your cabin, so this check is absolutely vital.
- Clean Burner Components: Over time, carbon and soot inevitably build up on the burner gauze and glow pin. This gunk stops the heater from igniting properly and burning efficiently. A careful clean can often bring it back to life, but if the gauze looks damaged, it needs to be replaced.
These jobs can be a bit fiddly and require a decent understanding of how the unit works. For many boat owners, getting a professional service is the best way to get some peace of mind. Our certified engineers are experts at this, making sure every component is clean, safe, and working just as the manufacturer intended.
With the current economic climate, we’re seeing more owners focusing on extending the life of their boats rather than buying new. This makes professional maintenance more important than ever—it’s shifted from a nice-to-have extra to a crucial step in protecting your investment.
Maintaining Your Solid Fuel Stove
For many boaters, especially on the UK’s canals, you just can’t beat the radiant, cosy heat from a solid fuel stove. But with that cosiness comes a responsibility to keep up with maintenance. You have to stay on top of it to prevent serious risks like chimney fires and carbon monoxide poisoning.
Before you even think about lighting that first fire of the season, there are a few key jobs you need to tackle. Getting these done now is fundamental to keeping your stove safe and efficient through the long, damp UK winter.
Essential Stove Winterisation Tasks
The single most important job is to clean the flue. As you burn solid fuel, a sticky, highly flammable substance called creosote builds up inside your chimney. If that deposit gets too thick, it can easily ignite and cause a dangerous chimney fire. A set of flue brushes is a tiny investment that is absolutely essential for every boater with a stove.
Once the flue is clean, turn your attention to the stove itself:
- Inspect Fire Bricks and Baffles: Check the internal fire bricks for any big cracks or signs of crumbling. These bricks are there to protect the stove’s metal body from the intense heat, so any damaged ones should be replaced.
- Check Rope Seals: The rope seal around the door is what creates an airtight seal, letting you control how fast the fire burns. If it’s frayed or looks compressed, air will leak in, making the fire burn too quickly and just waste fuel.
- Protect from Rust: Give the stove body a good wipe-down with an oily rag. This leaves a thin, protective film that will help ward off rust in the damp winter air.
Properly servicing diesel-burning appliances on your boat isn’t just about making sure they work when you flick a switch. It’s a critical safety measure. A full service before winter means you can enjoy your boat safely, whether you’re living aboard full-time or just visiting on weekends. It’s your ticket to a worry-free winter.
Preparing Your Hull, Deck, and Interior
Proper winterising goes way beyond the engine room and the plumbing. If you want your boat to survive a classic UK winter unscathed, you’ve got to protect its structure, both inside and out. The damp, cold conditions are a perfect breeding ground for mould, mildew, and corrosion—all things that can cause serious long-term damage if you let them get a foothold.
This part of the job is all about creating a barrier against the elements while making the interior as unwelcoming as possible for damp and pests. A bit of graft now will save you from that sinking feeling of opening up a musty, damp boat and facing a long list of repairs come spring.
Protecting Your Exterior Surfaces
Your boat’s first line of defence against winter is its exterior. Relentless rain, snow, and ice can really take a toll on paintwork and deck fittings if they aren’t prepped properly.
Start with a really thorough, top-to-bottom clean. This isn’t just about looking smart; you need to get rid of all the salt, grime, and bird droppings that can stain and corrode surfaces over the winter months.
Now is also the perfect time to give all your deck fittings a close inspection. Check the sealant around stanchions, cleats, and windows for any sign of cracking or pulling away. Even a tiny gap is an open invitation for water to seep into your boat’s core, which can lead to rot. Any dodgy-looking sealant should be dug out, cleaned, and replaced with a proper marine-grade sealant.
For those on steel-hulled narrowboats, hunt down any chips or scratches in the paintwork and touch them up to stop rust from taking hold. If you spot anything more serious, it might be worth getting in touch with specialists who offer mobile boat welding services to sort it out before it gets worse.
Choosing the Right Winter Cover
A good cover is one of the best investments you can make, especially if your boat is staying in the water for the winter. It has to be tough enough to handle the weight of snow and battering winds without sagging or tearing.
- Custom Canvas Covers: A well-made canvas cover, held up by a solid frame, is a fantastic long-term option. That frame is crucial—it stops water from pooling and makes sure air can circulate underneath.
- Heavy-Duty Tarpaulins: This is the budget-friendly choice, but make sure you get a high-quality, durable one and tie it down securely. A tarp flapping in the wind all winter will chafe your boat’s finish to bits.
Whatever you choose, proper ventilation is absolutely key. Your cover must have vents or be set up in a way that allows air to move freely. A completely sealed-up boat is just a recipe for condensation and mould.
Banishing Interior Damp and Mildew
Inside the cabin, your number one enemy is moisture. A damp, sealed-up boat is a playground for mould and mildew, which will leave you with nasty smells and ruined soft furnishings. The goal here is to get the interior as dry and well-aired as possible.
Start by getting everything you can off the boat. All your textiles—cushions, bedding, curtains, clothes—should be taken ashore. These things act like sponges, soaking up any moisture in the air and becoming ground zero for mould. If they absolutely have to stay on board, prop all the cushions up on their sides to get as much air circulating around them as possible.
The most common mistake boaters make is sealing the boat up tight. A completely sealed cabin traps moisture, leading to condensation every time the temperature drops. Your best defence is a combination of removing moisture and encouraging constant airflow.
Final Interior and Electrical Checks
Next, get every last scrap of food out of the galley. Open packets, tins, even sealed jars—they can all attract rodents and other pests looking for a warm winter home. Give all the cupboards a good clean to get rid of any crumbs.
To actively fight moisture, put some dehumidifiers in the cabin. Those passive moisture-absorbing crystal traps are a good, cheap option, but you’ll need to check on them and empty them out from time to time. If you’ve got a reliable shore power connection, a small, low-wattage electric dehumidifier is a more powerful solution.
Finally, get some air moving through the interior. Leave all the locker doors, cupboards, and drawers slightly ajar. After cleaning the fridge, prop its door open to stop it from going mouldy. These simple tricks allow air to circulate, preventing damp, stagnant air from settling in enclosed spaces.
As for your batteries, disconnect them to stop them from slowly draining over the winter. The best practice is to take them off the boat entirely, store them somewhere cool and dry, and hook them up to a smart trickle charger to keep them in good health.
Common Questions About Winterising Your Boat
Even with the best checklist in hand, it’s natural to have a few nagging questions when you’re tackling a job as critical as winterising your boat. After all, getting it wrong can lead to some seriously expensive repairs come spring. We get asked these all the time, so let’s clear up some of the most common queries we hear from boat owners.
Do I Really Need Antifreeze if I Drain the Water Systems?
Yes, you absolutely do. This is probably the biggest—and riskiest—shortcut we see people tempted to take.
Even if you meticulously drain every tap and blow compressed air through the lines, it’s virtually impossible to get every last drop of water out. Little pockets will always get trapped in low spots, within pump housings, or around threaded fittings. That’s all it takes. When that tiny amount of water freezes, it expands with enough force to crack an expensive pump or split a pipe wide open. Think of non-toxic marine antifreeze as cheap insurance. It’s the only way to be completely sure your plumbing is safe from the frost.
Should My Boat Stay in the Water or Be Hauled Out?
This one often comes down to your boat’s design and what your marina allows. For a lot of narrowboats and canal barges here in the UK, staying in the water is standard procedure. If that’s your plan, you need to be 100% confident that your bilge pumps are in perfect working order and that all your through-hull fittings are sound and not weeping.
Hauling out onto the hardstanding is definitely the safer bet for the hull, protecting it from potential ice damage, though this is less common for inland waterway vessels. It also makes it a doddle to get to any underwater gear for maintenance. The downside, of course, is the cost. Always double-check your marina or mooring’s policy before making a decision.
Relying solely on a heater is a high-risk gamble. A shore power failure, tripped breaker, or heater malfunction could leave your boat completely unprotected from a freeze. A full winterization of the engine and plumbing is the only reliable method.
Can I Just Leave a Small Heater On All Winter?
While a small heater can be a useful part of your winter strategy, it should never be your main defence against freezing. The risk is just too high. Imagine a power cut at the marina on the coldest night of the year, a dodgy extension lead failing, or the heater itself giving up the ghost. Suddenly, your boat’s systems are completely exposed.
The only guaranteed way to prevent freeze damage is a full winterisation using antifreeze in the engine and plumbing. Once that’s sorted, by all means, use a low-wattage tube heater. It’s a brilliant way to take the chill out of the air, fight off condensation, and stop the cabin from feeling damp and miserable. Just think of it as a tool for comfort, not a substitute for proper protection. It’s also vital to ensure any fuel-burning appliances are well-maintained; our guide on how to prevent carbon monoxide poisoning has more details on that.
Our Services
At Marine Heating Solutions, we know that keeping your boat safe and sound through the winter is a top priority. Whether you need a professional service for your Webasto or Eberspacher heater, a safety check on your solid fuel stove, or advice on the best heating solution for your vessel, our certified engineers are here to help. Make sure your boat is ready for the cold!
For quotes and bookings, call or email us here.
