How to Winterise Pressure Washer Properly

A frozen pressure washer is rarely a small problem. Water expands as it freezes, cracking pumps, valves, hoses, guns and fittings that may have worked perfectly the day before. Knowing how to winterise pressure washer equipment properly protects an expensive working asset, avoids avoidable downtime and gives you a machine that is ready when the next job comes in.

For commercial users, winterisation should be part of the shutdown routine whenever a machine will be stored in an unheated workshop, van, container or yard. One hard frost can be enough to cause damage, particularly on machines with brass pump heads, detergent systems and long hose runs. Do not assume a pressure washer is safe because it has been drained at the trigger gun. Water remains inside the pump, unloader, inlet system and lance.

When does a pressure washer need winterising?

Any pressure washer exposed to temperatures near or below 0°C needs protection. In the UK, this includes machines left in vans overnight, equipment stored in sheds and workshops with no heating, and static systems installed in external plant areas.

A machine used every day may not need a full winterisation process after each job if it is kept somewhere reliably heated. However, it still needs draining if there is any chance it will sit in freezing conditions. Petrol, diesel, cold water and hot water pressure washers all need attention, although hot water machines have additional components to consider.

If you operate a mobile valeting setup or a contractor’s van pack, be especially careful. The van may feel protected, but its contents can still freeze overnight. Insulation slows the cold down - it does not guarantee frost protection.

What you will need

The key product is a suitable pressure washer antifreeze or pump protector. This is not simply about preventing ice. A quality pump protector displaces residual water and leaves internal seals and moving parts lubricated during storage.

Use a product made for pressure washer pumps and follow its dilution instructions. Vehicle engine coolant is not always suitable, particularly where there is a risk of contact with detergent systems or food-sensitive cleaning environments. Never rely on salt, screenwash or improvised mixtures. They can damage seals, corrode components or leave residues where you do not want them.

You will also need a clean water supply for flushing, a bucket or container for the antifreeze solution, and appropriate PPE for the chemical being used. Keep the machine’s operating manual to hand if it specifies a particular procedure or antifreeze type.

How to winterise a pressure washer step by step

1. Flush out detergents and chemicals

Before draining the machine, run clean water through the detergent pickup and the pressure washer. This matters more than many operators realise. Traffic film remover, sodium hypochlorite, snow foam and other chemicals left in the system can attack seals, valves and injectors while the machine is standing.

Place the detergent tube in clean water and run the machine at low pressure until no chemical remains. If your machine uses an onboard detergent tank, empty it and rinse it where practical. On machines with separate chemical dosing systems, follow the manufacturer’s flushing procedure.

Do not leave sodium hypochlorite in any washer over winter. It is effective when used correctly, but it is not a storage fluid.

2. Shut down safely and release pressure

Turn off the burner on hot water machines first and allow the unit to run briefly on cold water. This helps cool the coil and prevents unnecessary heat stress at shutdown. Then switch off the machine, close the water supply and squeeze the trigger to release trapped pressure.

Disconnect the inlet hose, high-pressure hose and lance where possible. Coil hoses without tight bends and keep the ends clean. A hose may survive a light frost better than a pump, but water trapped in the hose can still cause splitting or damage to couplings.

3. Drain as much water as possible

With the water supply disconnected, start the pressure washer for a very short period - usually no more than a few seconds - to purge the bulk of the water from the pump. Keep the trigger open while doing this.

This step is useful, but it is not the finished job. Running a machine dry for too long can damage pump seals, and it will not remove all water from internal passages. Treat it as a preliminary drain, not your only frost-protection measure.

On a petrol or diesel washer, follow the machine’s normal start and stop procedure. For electric machines, make sure the supply is isolated before handling plugs, leads or electrical connections in damp conditions.

4. Draw pump protector through the system

Mix the pressure washer antifreeze according to the product instructions, then place the inlet hose or detergent pickup arrangement into the solution. The correct method depends on your machine design. Some machines can draw the fluid through the low-pressure inlet; others require a pump saver attachment fitted to the water inlet.

Run the machine only until the coloured antifreeze solution appears from the outlet or trigger gun. Once it does, stop the machine. This confirms that the pump, internal valves and outlet circuit contain frost-protection fluid rather than water.

For machines with a hose and lance connected, run the solution all the way through those components as well. If you remove the hose for storage, protect the pump first, then drain the hose separately. The goal is to leave no vulnerable water pockets behind.

5. Protect hot water washers properly

A hot water pressure washer needs the same pump protection as a cold water unit, plus careful attention to the heating system. Never run the burner while antifreeze is moving through the machine. The burner must be off throughout the winterisation process.

Allow the boiler and coil to cool before beginning. Drain and protect the pump side as described above, and check any external filters, float tanks and exposed pipework. If the washer has a water softener or frost-protection device, inspect it as part of the routine, but do not assume it removes the need for manual winterisation.

On larger static or industrial systems, there may be more than one pump, chemical line, hose reel or outlet point. Each circuit must be included. This is where a rushed five-minute shutdown can become an expensive spring repair.

6. Store the machine for the conditions it will face

Store the pressure washer in a dry, secure area where it cannot be exposed to standing water or severe temperature swings. Keeping it indoors is preferable, but a machine in an unheated building still needs antifreeze protection.

Keep the machine upright where its design requires it. Check that the fuel tank cap is secure on petrol and diesel units, and make sure ventilation is available in the storage area. If a machine will be laid up for several months, consider the fuel condition too. Old petrol can cause starting and carburettor problems, while diesel systems benefit from clean, suitable fuel and a water-free tank.

Common winterisation mistakes

The most common mistake is simply draining the hose and assuming the pump is empty. Internal pump chambers, bypass valves and unloader assemblies retain water long after the trigger stops flowing.

Another is running the pump dry for too long in an attempt to clear it. A few seconds is usually enough to expel bulk water. Extended dry running creates a different failure risk by overheating or scoring pump components.

Do not forget accessories. Surface cleaners, telescopic lances, hose reels and washdown hoses can all hold water. If they are stored in a freezing van or external unit, drain them before packing away. A split hose or seized swivel can hold up a job just as effectively as a damaged pump.

Finally, do not use the wrong antifreeze because it happens to be on the shelf. The small saving is not worth a damaged seal kit, contaminated system or pump rebuild.

Before putting the washer back into service

When temperatures improve, reconnect the clean water supply and flush the antifreeze from the system before carrying out normal cleaning work. Run water through the pump, hose and lance until it is fully clear. If the washer is used in food preparation areas, agricultural settings or any hygiene-sensitive application, take extra care to flush every part of the working circuit.

Inspect the inlet filter, hose connections, gun and lance for leaks before sending the machine back out. On hot water equipment, check fuel, burner operation and water flow before relying on it for a full day’s work. A quick pre-use check is far cheaper than finding a problem on site.

For fleets, winterisation is best managed as a logged maintenance task rather than left to memory. Mark which machines have been protected, where they are stored and when they are due back into service. This is particularly useful where several operators share equipment.

A pressure washer earns its keep when it starts, pumps and cleans without drama. Give it ten minutes of proper winter protection now, and you are far less likely to be paying for a pump repair when work is waiting.