One Cold Night In A Van Cracks A Pump Head. It Is Not A Warranty Claim.

Water expands by roughly nine per cent when it freezes. A pump head is a rigid, sealed casting with water trapped inside it.

That is the whole problem, and it is why frost damage is the second most common pressure washer failure we repair, after water starvation. It clusters in November and February; it arrives in batches after the first hard night of the season, and it is almost always excluded from warranty because it is preventable.

Five minutes in October prevents it.

Where the water actually hides

After use, a machine looks empty. It is not. Water stays in:

• The pump chambers, which are where the expensive damage happens
• The inlet and outlet manifolds
• The unloader valve, a complex casting full of small passages
• The hose, the lance and the gun
• The detergent injector and chemical lines
• The heating coil on hot water machines, which holds a considerable volume
• The inline filter housing

Draining the hose and standing the machine upright empties almost none of that. It is the bit everyone gets wrong.

The reliable method: antifreeze through the pump

This is what any machine that earns money should get. It takes about five minutes.

1. Finish the job, then release the pressure. Turn off the machine, disconnect the water, and squeeze the trigger until the flow stops.
2. Disconnect the water supply and the high-pressure hose.
3. Put a container of pump antifreeze, or a suitable non-toxic glycol solution, at the inlet.
4. Run the machine briefly until the antifreeze appears at the outlet.
5. Stop and store.

The antifreeze occupies the space water would have and leaves a film that stops seals from drying out over the winter.

Use proper pump antifreeze. Automotive coolant is not always compatible with pump seals. Screenwash is mostly water and offers very little protection at the concentrations sold.

The basic method: drain and purge

Better than nothing, less reliable, and it fails when somebody is in a hurry, which in November is most people.

Disconnect everything, release the pressure, tip the machine to drain, then blow low-pressure compressed air through the inlet to clear the internal passages. Drain the hose, lance and gun separately.

The simplest method of all

Keep it somewhere that does not drop below freezing.

A van is not frost protection. Van interiors get colder overnight than most people expect, and vans are where the clear majority of frozen pumps happen. If the machine lives in one, it needs the antifreeze treatment every time from October.

Petrol machines: the extra steps

Petrol and diesel machines need everything above, plus engine attention.

Fuel. Either drain the tank and carburettor completely, or fill the tank and add a fuel stabiliser. Half a tank of untreated petrol over a winter is the worst option, because ethanol absorbs moisture and the fuel degrades into varnish that blocks jets.

Engine oil. Change it before storage, not after. Old oil holds acids and moisture that corrode internals while the machine sits.

Spark plug. Remove it, put a small amount of oil into the cylinder, pull the starter slowly a couple of times to distribute it, then refit. This prevents bore corrosion.

Battery, on electric-start machines. Remove it, keep it charged and store it somewhere frost-free.

Air filter. Clean it before storage so it is ready in spring.

Full winter storage, if it is going away until March

Beyond frost protection, worth doing:

• Change the pump oil first. Old oil holds moisture and acids, and four months of that against internal surfaces causes corrosion.
• Clean and dry the nozzles, because deposits harden over winter and are far harder to shift later.
• Rinse the detergent system through with clean water.
• Coil the hose in large loops. Tight, cold coils set a permanent memory into the hose.
• Store it off the floor, covered but not sealed in plastic, which traps condensation.
• Leave the trigger unlocked and pressure released so the gun spring is not compressed all winter.

If it has already frozen

Do not switch it on. This matters most. Running the motor against ice inside the pump turns a frozen machine into a broken one, and can take the motor with it.

Do not apply direct heat. A blowtorch or heat gun cracks castings through thermal shock and damages seals.

Move it somewhere warm and let it thaw slowly and completely, which can take several hours or overnight for a large machine. Then connect water, open the trigger and confirm water flows freely through before starting. Listen for rattling or pulsing and check for weeping around the pump head and unloader.

If any of that is present, stop and get it looked at.

Frequently asked questions

How do I winterise a pressure washer?

Release the pressure, disconnect the water and hose, then draw pump antifreeze through the machine until it appears at the outlet, and store it above freezing. Drain the hose, lance and gun separately. For seasonal storage, change the pump oil first and rinse the detergent system through.

Will frost damage a pressure washer?

Yes, and it is the second most common failure we repair. Water expands as it freezes, and the pump head is a rigid sealed casting, so trapped water cracks housings, splits valves and destroys seals. It is generally excluded from warranty because it is preventable.

Can I use car antifreeze in a pressure washer?

Use a purpose-made pump antifreeze rather than automotive coolant, which is not always compatible with pump seals. Screenwash is unsuitable as well, since it is mostly water and provides little protection at the concentrations it is sold at.

How do I store a petrol pressure washer over winter?

Do the pump antifreeze routine, then either drain the fuel system completely or fill the tank and add a stabiliser. Change the engine oil before storage, fog the cylinder through the spark plug hole, remove and charge the battery on electric-start machines, and clean the air filter.

What should I do if my pressure washer has frozen?

Do not switch it on and do not apply direct heat. Move it somewhere warm and let it thaw slowly and completely, then connect water and confirm it flows freely before starting. Listen for rattling or pulsing and check for weeping around the pump head, and stop if you find either.

The bottom line

A container of pump antifreeze costs very little. A cracked pump head costs a great deal more, plus the days you cannot work.

Do it in October, before the forecast makes you think about it.

RealKleen stocks pump antifreeze and pump oil, and repairs frost-damaged machines of every brand in our workshop. Book a pre-winter service, and we will winterise it properly while it is with us.