Winterising Water Systems

A frozen water system is the most disruptive failure you'll deal with in a UK winter. A frozen pipe can split. A frozen pump can crack. A frozen tank can bulge and leak when it thaws. And when it happens, you discover it at 7am when you're trying to make coffee and nothing comes out of the tap.

This guide covers how to prevent water system freezing, how to winterise your van for storage, and what to do if everything is already frozen.

Understanding Freeze Risk

Water expands by 9% when it freezes. The expansion is what breaks pipes, pumps, and tanks. The key question is: how cold does it need to get before your system freezes?

The critical rule: If your van's interior temperature drops below 5°C for more than 8 hours, your water system is at risk. Below 2°C, it will freeze.

Prevention (While Living in the Van)

Keep the Van Above 5°C

If you're in the van, run your diesel heater on low continuously (12-15°C setting). The heat keeps the van interior — and everything inside it — above freezing. This is the single most effective prevention.

• A 2kW diesel heater uses 0.1-0.2L/hour on low
• Running 12h/day = 1.2-2.4L diesel = £2-4/day
• That's cheaper than repairing a split water system (£150-500)

The problem: If you leave the van for more than 12 hours (day trip, hiking, skiing), the heater is off, and the van cools to ambient temperature. Below-freezing ambient leaves your water system exposed.

Insulate Your Water Pipes

Pipes that run through unheated areas (under the van, in the garage bay, behind wheel arch panels) need insulation:

• Closed-cell foam pipe insulation (Armaflex or similar) — £5-10 for 2m at Screwfix. Split it lengthwise, wrap around pipes, tape the seam.
• Pipe wrap (foil-backed bubble wrap) — cheaper but less effective than Armaflex.
• "Trace heating" cable — an electric heating tape that wraps around the pipe. Cost: £20-40 for 5m. Power draw: 10-20W per metre. Runs on 12V or 240V. You leave it on when you're away from the van.

Where to prioritise: The pipe between your water tank and your pump (often the longest exposed run). The pipe from your pump to your hot water heater (usually shorter but runs through cold voids).

Heat Your Tank

Underslung tanks need a 12V heating pad (£25-40, 50-100W). Glue it to the tank base, wire it to a thermostat switch that activates at 3°C. The pad draws 4-8A when running. In a cold spell, it runs about 30-50% of the time.

Internal tanks need less protection because they're inside the van. If your van is heated, the tank is fine. If you leave the van for more than 12 hours, drain the tank — don't rely on insulation alone.

Open Cupboard Doors

Pipes running inside cupboards (especially under the sink, behind the kitchen unit) are in dead air spaces that stay colder than the main cabin. Open the cupboard doors to let warm air circulate.

Winterising for Storage (Van Parked Up)

If you're not using the van for 2+ weeks in winter, drain the water system completely.

Step 1: Drain the Fresh Tank

Open the tank drain valve (underslung) or tip the tank out (internal). Run the pump until it sputters (this empties the pump and most of the pipework).

Step 2: Blow Out the Pipes

With the pump off, disconnect the output hose from the pump. Use a bicycle pump or compressed air can (£5) to blow air through the pipes from the tap end backwards. This clears water from low points where it would pool and freeze.

Step 3: Drain the Hot Water Heater

If you have a water heater (immersion or gas), open the pressure release valve and the drain plug. Hot water heaters hold 5-15L of water. If that freezes, the heater coil splits and the unit needs replacing (£200-400).

Step 4: Add Antifreeze to Traps

Pour a cup of pink RV antifreeze (the potable-safe kind, not car radiator antifreeze — Boots or Amazon, £5-8) down each sink drain and the shower tray. This fills the P-traps and prevents them freezing. Without this, the trap freezes, the ice expands, and the pipe joint cracks.

Do NOT use car antifreeze (ethylene glycol) — it's poisonous and can contaminate your water system. Use propylene glycol (food-safe RV antifreeze, sold as "Aqua-Safe Winteriser" or "Milenco Winteriser").

Step 5: Remove the Pump

If possible, remove the pump and store it inside your house. A frozen pump is the most common winter failure. Store it in a warm room and reinstall in spring.

Step 6: Leave Taps Open

Open all taps (hot and cold) to the midway position. This relieves pressure if any residual water freezes (the expanding ice pushes out through the open tap instead of splitting the pipe).

What to Do If Everything Is Frozen

Don't Turn on the Pump

If the water is frozen and you turn on the pump, the pump runs against a blocked pipe. The pump impeller breaks or the pipe fitting bursts. Check before you pump.

Check the Temperature

If the van interior is above 0°C, the frozen water will thaw naturally in 2-4 hours. Turn on the diesel heater to speed it up. The pipes closest to the heater will thaw first.

Use a Hair Dryer (Not a Heat Gun)

If you need water urgently, use a hair dryer on medium heat to thaw the frozen section. Hold it 10-15cm from the pipe and move it back and forth. A heat gun is too hot and will melt the pipe.

Thawing the Tank

• Internal tank: Move it near the heater. It'll thaw in 1-2 hours.
• Underslung tank: Park the van in direct sun (if there is any). Or pour warm (not boiling) water over the tank outlet. Or run the engine for 30 minutes — the heat from the exhaust and engine block warms the underside of the van.

After Thawing

• Check all pipe joints for leaks (the freeze expansion may have cracked a fitting)
• Run the pump and watch for drips at every joint
• If a pipe has split, you need to replace that section (Jubilee clips + replacement hose from Screwfix)

Winter Checklist

The damage from a single frozen pipe costs more than all the prevention measures combined. If you know you'll winter van life in the UK, spend the £50-100 on insulation and a heat pad before the first cold snap. It's cheaper than learning the hard way.