How to Drain Down a Caravan or Motorhome Water System for Winter
Emptying the fresh-water tank is not the same as draining the complete water system.
Water can remain inside the heater, pump, filter housing, mixer taps, toilet valve, shower hose and low sections of pipework. It may only be a small amount, but if it freezes it can expand and split a fitting or damage an internal valve. The problem often stays hidden until the system is refilled in spring and the leak appears.
A proper drain-down does not take long, but it needs to cover every part of the system. This guide explains the general process used on many UK caravans and motorhomes, as well as the important differences between Truma, Alde and Thetford equipment.
Important: Water-system layouts and drain-valve arrangements vary between vehicles. Always check the handbook for your caravan or motorhome and the instructions for the exact heater, pump and toilet fitted. Manufacturer instructions take priority over general guidance.
When should you drain the water system?
Drain the system whenever the vehicle will be left unused and freezing temperatures are possible. Do not wait for a prolonged cold spell. A single freezing night can be enough to damage a component containing trapped water.
It is also worth draining the system when the vehicle will be stored for a long period, even outside winter. Removing standing water helps prevent stale smells and makes recommissioning easier.
What you will need
Most drain-downs only require:
- The handbooks for the vehicle and fitted appliances
- A cloth or shallow container for small amounts of water
- Somewhere suitable to empty fresh and waste water
- A clean, dry place to store an external pump and filter assembly
- An optional purpose-designed low-pressure drain-down kit
Allow the water heater to cool before starting. Switch off its gas and electric heating functions, disconnect any direct mains-water supply and turn off the water pump.
Step 1: Empty the external and onboard tanks
If the caravan uses an Aquaroll or another external water container, remove the pump and allow the container to empty. Disconnect the pump assembly from the vehicle and shake out any obvious water before storing it somewhere clean and dry.
If the vehicle has an onboard fresh-water tank, locate and open its drain valve. Keep the filler cap open if the vehicle handbook instructs you to, as air needs to enter the tank for water to leave freely.
Motorhome grey-water tanks should be emptied at a proper disposal point. Remove sink and shower plugs so water cannot remain trapped in the waste outlets.
Step 2: Open every tap and shower outlet
Open every mixer tap and place it in the centre position so the hot and cold sides are both open. Include:
- Kitchen tap
- Washroom tap
- Internal shower
- External shower, if fitted
- Any outside tap or wash point
Lower the shower head into the shower tray and allow its hose to drain. If it can be removed easily, disconnect it and shake out the remaining water. Shower hoses are one of the easiest places to overlook.
Leave the outlets open while the rest of the system drains. On many vehicles they should remain open throughout storage, but check the vehicle handbook before leaving them that way.
Step 3: Drain the water heater
The water heater is one of the most important parts of the system to empty. Its drain valve is normally fitted close to the appliance, but the design and operating position depend on the system.
Open the correct drain valve and look underneath the vehicle to make sure water is actually flowing. Do not assume that moving the lever or control has emptied the heater. A blocked, kinked or incorrectly positioned drain hose can prevent a complete drain-down.
If the manufacturer states the capacity of the water container, checking that a similar quantity has drained is a useful way to spot a restricted outlet.
Truma Combi with FrostControl
Truma FrostControl opens automatically when the temperature at the valve falls below approximately 3°C. It can normally be closed manually again once the temperature around the valve reaches approximately 7°C.
However, FrostControl should not be treated as a replacement for a full drain-down. Opening it drains the water held inside the Truma Combi, but it does not guarantee that the fresh-water tank and all the vehicle's pipework will empty. Those parts depend on how the vehicle manufacturer installed the water system.
For winter storage, switch off the pump, open the taps and manually open FrostControl rather than waiting for cold weather to trigger it.
If your existing valve is damaged, view the Truma FrostControl Valve Set. Check the heater model, pipe type and connection size before ordering.
Truma Boiler, Ultrastore and Therme systems
Not every Truma water heater uses FrostControl. Older Truma Boiler and Ultrastore installations usually have a manual safety or drain valve. The Truma Therme also uses drain and aeration valves that must be opened correctly.
The procedure and expected amount of water vary by appliance. As examples, Truma identifies approximately 10 litres for its gas and gas/electric Boiler, 14 litres for the electric Boiler and 5 litres for the Therme. Check the exact appliance instructions rather than identifying it by appearance alone.
Replacement parts such as the Truma Ultrastore 2.8 bar Safety Drain Valve must be matched to the original system and pipework.
Alde heating systems
An Alde system contains two separate circuits:
- The domestic fresh-water side that supplies hot water to the taps
- The sealed heating circuit containing glycol fluid
The domestic water side must be drained when there is a risk of frost. The glycol heating circuit should not be emptied as part of an ordinary winter water drain-down.
Alde advises switching off the fresh-water pump and heating system, opening every tap in the centre position, placing the shower head in the tray and opening the yellow drain valve or valves near the boiler. Some vehicles have separate hot and cold drain valves, so check for more than one.
The Alde space-heating system can normally still be used with the domestic hot-water cylinder empty, but follow the handbook for the exact installation.
Whale and other water heater
Whale installations differ between vehicles and appliance generations. Use the dedicated drain point and follow the instructions for the exact model. Do not assume that opening the main fresh-water tank drain will also empty the water heater.
Step 4: Drain the pump, filter and water inlet
The correct procedure depends on whether the vehicle has an external submersible pump or an onboard pressure pump.
External submersible pump
Remove the pump from the water container, disconnect it from the vehicle and let it drain. Shake out the hose and pump assembly gently, then store it in a clean, dry place. Protect the electrical contacts and water connection from dirt.
Onboard pressure pump
Open the system drain points and follow the pump manufacturer's winterisation instructions. Some manufacturers specify a brief purge procedure, while other pumps should not be run dry. Do not leave a pump running without water unless the instructions for that exact pump say it is permitted.
If a removable filter or strainer is fitted, inspect it for trapped water. Water can remain around the filter housing and its threads even when the rest of the system appears empty. Remove or drain the filter if the manufacturer recommends it, then store any reusable components clean and dry.
You can browse our water pumps and spares and water hoses and fittings if anything is found damaged during the drain-down.
Step 5: Do not forget the toilet flush system
The toilet may have its own flush-water reservoir or may take water from the vehicle's main fresh-water system. The correct method depends on the toilet model.
Toilet with a separate flush-water tank
Drain the reservoir through its proper drain tube or drain point, then operate the flush as instructed to remove water remaining in the pump and flush mechanism. Empty and clean the waste-holding cassette as normal.
Toilet supplied by the vehicle's main water system
The toilet solenoid or flush valve can retain water. Some Thetford manuals instruct the user to hold the flush control open while the central water system is draining. Follow the instructions for the exact toilet model rather than repeatedly running its electric flush after the system is empty.
Use only a seal-care product approved for the toilet model. Advice on oils differs between older and newer Thetford toilets, so a model-specific product such as Thetford Seal Lubricant is the safest general choice. Do not use Vaseline.
Step 6: Check the places where water commonly hides
Before finishing, check each of these if fitted:
- Shower head and the lowest loop of shower hose
- External shower or outside wash point
- Water inlet socket and connecting hose
- Filter housings and pump strainers
- Toilet flush reservoir, pump or solenoid valve
- Accumulator or expansion vessel
- Hot and cold low-point drains
- Pipes running below beds, lockers or raised floors
- The water heater's discharge hose beneath the vehicle
An empty tank gauge does not prove these components are empty.
Should you blow the system through with compressed air?
A purpose-designed low-pressure drain-down kit can help remove water left in pipework after gravity draining. It is particularly useful on systems with long pipe runs or awkward low points.
It must be used exactly as its manufacturer instructs. Floë specifies a maximum of 15 psi, or approximately 1 bar, for its touring caravan and motorhome kits. Never connect an unregulated workshop compressor or an unrestricted mains-water supply to the caravan's plumbing. Excessive pressure can damage taps, non-return valves, filter housings and appliance connections.
Thomas Touring stocks dedicated versions for Truma Ultraflow water inlets and Whale water connections. Confirm the inlet type before choosing a kit.
Compressed air is an additional step, not a substitute for opening the water heater and tank drain valves.
Final checks before storage
Before leaving the vehicle:
- Confirm that water has discharged beneath every relevant drain point
- Leave taps and drain valves in the storage position stated in the handbook
- Make sure the shower hose and external outlets are empty
- Remove or drain filter components where required
- Empty the toilet flush tank and waste cassette
- Store external pumps and hoses clean and dry
- Place a note near the controls stating that the water system is drained
That final note can prevent somebody switching on the pump or selecting hot-water mode before the system has been refilled.
Bringing the water system back into use
When the vehicle is needed again:
1. Inspect the visible pipework, pump, heater connections and drain valves.
2. Refit any filter, pump or hose removed for storage.
3. Close every drain valve according to the appliance instructions.
4. If a Truma FrostControl will not reset, warm the area around the valve. It generally needs to be approximately 7°C before it can be closed manually.
5. Fill the fresh-water tank or connect the external water container.
6. Switch on the pump and open a hot tap until water flows steadily without air.
7. Repeat at every hot and cold outlet, including the shower and toilet flush.
8. Check carefully for leaks around taps, filters, pumps, toilet valves and the water heater.
9. Clean and sanitise the system using a suitable potable-water product, following its dosing and flushing instructions.
Do not switch on a storage water heater until its water container is full. A steady flow from the hot taps normally confirms that air has been displaced, but always follow the appliance's filling procedure.
For a wider explanation of tanks, pumps, pipework and waste systems, see our caravan and motorhome water-system guide.
Quick winter drain-down checklist
- Water heater switched off and allowed to cool
- Water pump switched off
- External container or onboard fresh-water tank emptied
- Grey-water tank emptied at a suitable disposal point
- All hot and cold taps open in the centre position
- Internal and external showers drained
- Water-heater drain valve opened and flow checked
- Pump, filter and water inlet checked for trapped water
- Toilet flush system and cassette emptied
- Any manufacturer-approved air purge completed
- Taps and drain valves left in their specified storage positions
- Note placed near the controls before storage
Frequently asked questions
Is emptying the fresh-water tank enough?
No. Water can remain in the heater, pump, pipes, filters, taps, shower hose and toilet system after the tank is empty. Each part must be drained using the appropriate valve or procedure.
Will Truma FrostControl drain the complete caravan or motorhome?
No. FrostControl drains the Truma Combi water container. Whether the fresh-water tank and pipework drain depends on the vehicle's installation, so the remaining system must be dealt with separately.
Should mixer taps be left open over winter?
Many manufacturers advise leaving them open in the centre position so the hot and cold sides can drain and remain unpressurised. Check the handbook for your vehicle and tap system.
Should I run the water pump dry?
Only if the instructions for that exact pump tell you to do so. Pump designs differ, and running some models without water can cause damage.
Do I need antifreeze in the fresh-water system?
Most UK caravan and motorhome procedures are based on completely draining the fresh-water system. Never use automotive radiator antifreeze in a potable-water system. If the vehicle or appliance manufacturer specifies a particular potable-water winterising product, follow its instructions exactly.
Can the heating still be used after the water has been drained?
Some combined systems, including many Truma Combi and Alde installations, can provide space heating with the domestic water side empty. Do not select a hot-water function on an empty appliance unless its manual explicitly allows it.
Need help identifying a valve, pump or fitting?
If you find a cracked fitting, leaking valve or damaged pump while draining the system, send Thomas Touring a clear photograph of the part and the model plate from the appliance or vehicle. Measurements and any visible part numbers will help us identify the correct replacement.
You can contact the Thomas Touring team or browse our caravan and motorhome taps and fittings.