Winter systems
Truma Frost Valve Guide
A practical guide to the Truma Frost Control valve so you can protect your water system, avoid surprise draining, and get back on the road with confidence.
Quick help
What the valve does
The Truma frost control valve is a safety drain valve designed to protect your boiler and water system from frost damage. If you see water pouring from underneath your motorhome, it is almost certainly the Truma frost control or frost protection valve opening automatically to protect the boiler from freezing damage. When temperatures drop, battery support is too low, or the valve is opened manually, it releases water from the boiler to help prevent costly repairs.
Understanding how this valve works makes winter setup much less stressful. It is there to protect the boiler, not to cause a fault, and once conditions are right it can usually be reset quickly and safely.
Why it opens
There are three main reasons the Truma frost control valve trips. The first is low ambient temperature, usually around 3ยฐC to 5ยฐC or lower around the valve housing. The second is low leisure battery voltage, often around 11V, which can affect the system and lead to draining, but this is normally on electrically operated valves which are less common. The third is manual draining, where the valve has been opened intentionally as part of winterising or maintenance.
How to reset it
- Turn off the water pump.
- Check the temperature and heat the van if needed so the valve area is warm enough to reset.
- Reset the rotary switch to the operation position.
- Push the button in until it stays engaged.
- Refill the system by turning the pump back on and opening the hot taps to bleed air from the boiler and pipework.
Pro tip: You can run the hot air heating without water in the boiler to warm the van above the reset temperature before resetting the valve. A small hair dryer can also be used gently to warm the valve housing if the area is especially cold.
Common mistakes
Many owners think they have a leak when the boiler drains underneath the van, when in reality the Frost control valve is doing exactly what it is designed to do. Others try to reset it before the valve body is warm enough, or forget to check battery voltage before refilling the system.
Best practice
Check the valve before every cold-weather trip, keep the surrounding area from getting too cold, and test your refill routine at home so you know exactly how your setup behaves before you travel.
Truma boiler frost/drain down valve tutorial
Use this section as a clear visual walkthrough to help you locate the valve, understand why it opens, and manually reset it with confidence.
Where is the Frost control valve usually fitted?
It is commonly installed close to the Truma boiler, often in a seat box, service locker, or low-level cupboard. It is usually positioned where the drain pipe can run safely through the floor.
Why does my water keep draining out?
If water is pouring from underneath the motorhome, the Frost Control valve has most likely opened to protect the boiler. Low temperature around 3ยฐC to 5ยฐC or lower is the most common cause, but low leisure battery voltage or manual draining can also be responsible.
Can I stop it opening in winter?
You should not defeat the safety function. Instead, keep the area warm, use heating sensibly, and understand how to reset the valve correctly when conditions improve. (forcing this or overriding it can cause boiler damage in cold climates)
What should I check before refilling?
Make sure the water pump is off first, the rotary switch is back in the operation position, the button is fully engaged, and the valve body is warm enough to remain shut. Then turn the pump back on and open the hot taps to bleed air as the system refills.
Is it a fault if it opens while stored?
Not usually. If the van is left in cold conditions, the valve may open exactly as intended. That is why it is important to drain down properly and understand what the system is doing.
When should I get help?
If the valve will not reset when warm, continues draining unexpectedly in mild conditions, or shows signs of damage, it is worth asking a qualified technician to inspect the system.