Residual water in the pump head turns into an expensive crack in the frost

For a lot of people, the last wash day in October ends the same way: garden hose off, machine into the garage, door shut. Looks tidy. But that doesn't make your pressure washer frost-proof: there's still water sitting in the pump head, the trigger gun and the high-pressure hose, and you only find out in March, when the gun drips or the pump won't build pressure any more. Winterising takes less than a quarter of an hour once you know the order.

A pressure washer makes it through winter when there's no water left in the pump, gun and hose and the machine is stored in a frost-free room. You need both to protect the pump head, one step on its own isn't enough.

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Frost-proof means an empty machine in a frost-free room

Storing a pressure washer frost-proof means getting the residual water out of the pump, gun and hose and then keeping the machine in a room that stays above freezing all winter long.

Both halves matter just as much. In the manual for the K 1050 P, Kränzle sets out two things: drain the machine completely and store it in frost-free rooms over winter. Kärcher and Nilfisk say exactly the same in their guides. If you only drain it and then park it in an unheated garage, you're betting that there really isn't a single drop left inside. If you only store it somewhere warm but don't drain it, you've got a wet pump head all winter, and the frost on the way down to the cellar is enough for the first damage.

This applies to you whatever machine you run. Whether it's a compact pressure washer for the weekend car wash or a big unit with a hose reel: anywhere water runs under pressure, there are chambers, valves and seals that the water won't drain out of on its own. It's the small amounts that cause the trouble.

The right time is now. According to Google Trends, demand for pressure washers drops off sharply in autumn, and for many people the driveway wash season is over. At the end of October, nights in northern Germany are still sitting at six to seven degrees, and the first frosty night usually turns up without much warning. Winterise today and you do it in the dry and without rushing, instead of wrestling frozen couplings with cold hands in December.

Ice needs nine percent more space than water

Water expands by about nine percent when it freezes, and inside the closed system of a pressure washer the ice has nowhere to go. That's why the pump head, valves, gun or hose give way.

The pump head houses the parts that build the pressure: pistons, seals, valves and the switch that cuts the motor as soon as you let go of the trigger. On the Kränzle K 1050 the pump head is made of special brass. Brass handles pressure from the inside while the machine is running. Against ice slowly expanding in a closed channel, that doesn't help much. Typical damage is a hairline crack in the pump head, bent valves and seals pushed out of their seats.

Kärcher puts the consequence plainly in its own guide: even small amounts of residual water freeze, destroy seals and, in the worst case, the pump. That's the real point. You don't need a full tank for something to crack. A bit left in a valve seat or in the gun's grip is enough.

On top of that, frost damage isn't a material defect. Kränzle's warranty covers defects in material and manufacture and makes the operating manual part of it, including the requirement to store the machine frost-free. So a cracked pump head after a winter in the garage is usually on you. That's no reason to worry, just a good reason for the fifteen minutes winterising takes. Putting a pressure washer away frost-free is cheaper than any new pump head.

Inlet off, gun open, one minute of dry run at most

With almost every manufacturer, draining follows the same order: disconnect the water inlet, release the pressure through the gun, run the machine briefly without water and keep the trigger pulled until nothing more comes out.

Step one is the water inlet. Unscrew the garden hose from the machine's inlet and let the hose itself drain.

Then, with the machine switched off, pull the trigger so the pressure escapes from the high-pressure hose. Kränzle calls it a safety shut-off gun, but it works the same way on every machine.

Step two is the short dry run. Switch the machine on, hold the trigger down with the nozzle pointing at the ground, and the pump pushes the last of the water out of the pump head through the hose and lance. As soon as there's only air coming out, switch off. Timing matters here, because water cools and lubricates the seals in the pump. Kränzle's manual allows one minute without water at most, and in its own winterising video Kränzle even says just 20 seconds. Kärcher talks about half a minute or so.

We go with the strictest figure. On a compact machine, 20 seconds is in practice enough for hardly any water to come out. If you've got compressed air, you can blow the residual water out with that instead, which Kränzle lists as an alternative. If your machine has a detergent tank, fill it with about 0.2 litres of fresh water after emptying and run the machine briefly in detergent mode, as Kärcher describes. That stops the injector gumming up over winter.

After that, take the gun off the hose and hold it nozzle down while you pull the trigger all the way once more. The grip has its own valve, and that's exactly where a bit of water likes to hang around. One user report online sums it up: every spring a plastic part had burst, sometimes the gun, even though only a small amount of water had been left in the system.

Hose, inlet filter and foam lance dry separately from the machine

Once the pump is done, it's the accessories: drain the high-pressure hose and coil it without kinks, rinse the inlet filter on the water inlet and flush the foam lance with clean water before everything dries separately.

Lay the high-pressure hose out straight, lift one end and let the water run out. Then coil it in big, loose loops. A kink damages the pressure braid inside, and cold hoses go stiff, so a kink happens more easily in winter than in summer. The same goes all year round: walk round the car with the hose while washing and it's quickly dragged under a tyre. The Koch-Chemie Hose & Cable Guard Hose Roller Tyre Guide Rollers 2 pieces sit in front of the tyre and guide the hose or cable past it instead of letting it get trapped.

The inlet filter on the water inlet protects the pump from sand and particles coming out of the supply line. Kärcher recommends checking and cleaning the water filter once a year. Autumn is the best moment for it, because the filter should go into storage dry anyway. A lot of detailers treat the O-rings on the couplings with a little silicone grease before winter. Vaseline and other mineral oil products have no business on these seals, they make the rubber swell.

The foam lance is the one people forget. After the last wash, leftover snow foam solution stays in the bottle and the nozzle. Over winter the water evaporates, and whatever is left clogs the fine mesh inside the lance. Come spring, all you get is wet, runny foam. Before putting it away, fill the bottle with clean water and spray it out completely. How to dial the lance back in for thick foam afterwards is covered in our post Setting up a foam lance.

On machines with an oil bath, now is a good time to check the sight glass. If the oil is milky or grey, water has found its way into the pump, and then a service before storage makes more sense than a winter with the problem. For the bigboi WashR models, the manufacturer also requires a special antifreeze for the pump, pushed in through the water inlet, for storage longer than 30 days or when there's a risk of frost.

The garage is rarely frost-free in January

The most common mistake is where the machine is kept: unheated garages, carports and garden sheds drop below zero after several frosty nights in a row, even if they still feel mild in November.

Kärcher points out explicitly that garages and garden sheds can fall below freezing in a hard frost. In forums, users report exactly that: the machine stood in the garage for years until one cold winter brought a crack in the pump head. A carport isn't a storage spot, it keeps the rain off, not the frost. Frost-free means a cellar, a heated utility room or another room that stays at temperature through the winter.

The second mistake is doing half the job. Plenty of people just unscrew the garden hose and reckon the machine is empty. But the pump head stays flooded behind its valves, and the gun holds on to its water too. Without the short dry run and emptying the gun, exactly the amount that does the damage in a frost stays in the machine.

The third mistake only happens in spring. Start a machine that still has ice inside and the pump runs against a blockage that won't budge. If your pressure washer does end up in the cold after a cold snap, let it thaw out completely in a warm room first and check it for cracks and damp spots before you switch it on. And on antifreeze: for professional machines Kärcher names standard glycol-based automotive antifreeze. Screenwash is something else and doesn't belong in the pump. For consumer machines without manufacturer approval, draining thoroughly is the better way.

Winter washing without your own machine works in a self-service wash bay

With your pressure washer stored frost-free in the cellar, the easiest way to wash in winter is at a self-service wash bay, and for the pre-wash there a pump foam sprayer with a snow foam made for self-service washing does the job.

In winter you want to get road salt off the car every two to four weeks, especially out of the wheel arches, off the sills and out of the door shuts. The self-service bay has frost-protected equipment for that, but the pre-wash chemicals there are often more alkaline than a sealant would like. The Koch-Chemie Ultra Foam "Uf" 1000 ml / 1 litre is made precisely for the self-service wash. It sits at pH 8.5, between pH-neutral and strongly alkaline foam, and gets by on three to eight millilitres per car. So one litre covers plenty of winter washes.

That said, it doesn't replace a pre-cleaner for decontamination before polishing.

To take the foam with you, use the iK Sprayers "iK Foam" Pro 2 1.25 litre. The pump foam sprayer needs no power and no water connection, you pump it up and the safety valve limits the pressure at 3 bar.

Customers rate it 4.86 out of 5 stars from seven reviews on Trusted Shops and mainly praise the thick foam. To be honest about its limits: a pump sprayer foams a car, it doesn't rinse it. That's the job of the bay's lance, at the distance we explained in Washing your car with a pressure washer. And by the way, the pump sprayer also belongs in a frost-free room, emptied, after the last wash.

A quick aside on the new BMW M3: if you're taking your M3 with M Carbon ceramic brakes through the winter, be extra careful around the wheels in the self-service bay. Carbon-ceramic discs don't like point impacts, so use a soft wheel brush, keep tools away from the disc and no grease on the friction surface. The ever-bigger kidney grille may collect more bugs in summer, but in winter it's the salt on the wheels that deserves your attention.

That leaves the doors after the wash. Residual water on the rubber seals freezes solid overnight if you don't wipe them dry. How to prep the seals for that is in Treat your door seals before the first frosty night freezes the door shut. You'll find more pre-wash foams under Snow Foam.

Detailing1-Insight: Every autumn we get questions about the oil in the pump, most recently which oil goes into a bigboi WashR Pro. According to bigboi, it's a non-detergent engine oil rated SAE 10W/30 or 15W/40, with the first change due after 30 operating hours. Winter is the best time to check this, because the machine is being drained and cleaned anyway. What we don't recommend: putting a machine with milky oil into storage and hoping it still runs in March. Then water sits for months exactly where there should be a film of lubricant.