Going Away in Winter: Should You Turn the Water Off and Leave Your Combi Boiler On?
Yes — for a trip of a few weeks, turn the water off at the stopcock and leave your combi boiler on, with the heating set low. A combi heats your radiators from a sealed loop that doesn't need the mains supply, so turning the water off won't stop the heating working or harm the boiler. Leaving the heating on keeps the pipes above freezing, and turning the water off means that if a pipe does burst, it can't keep pouring water into the house.
That's the short answer. The rest of this post covers what to set the thermostat to, what to check before you leave, and the one thing that catches people out in a Scottish winter.
Why turning the water off doesn't stop a combi working?
It's the most common worry we hear: "If I turn the water off, won't the boiler fault, or overheat?"
It won't. A combi boiler does two separate jobs:
• Heating: the water that goes round your radiators is a closed loop. It's heated, circulated and cooled again, over and over, without drawing anything from the mains.
• Hot water: when you turn on a hot tap, the boiler heats cold mains water as it passes through.
Turn the stopcock off and only the second job stops — there's simply no hot water at the taps. The heating carries on as normal. Ideal Heating, one of the big boiler manufacturers, says the same: the heating water is in a closed loop, and a combi will shut itself down safely if it detects a problem.
Don't rely on the boiler's frost protection alone.
Most modern boilers have a built-in frost setting. The catch is what it protects: the boiler itself, not the pipes around your house. A pipe in the loft, under a suspended floor or along an outside wall can freeze long before the boiler thinks it's cold enough to fire up.
That's why Scottish Water's advice for going away in cold weather is to leave the heating on continuously with the thermostat set low, rather than switching it off and trusting frost protection.
Watch out for "holiday" or "away" buttons, too. On some boilers and thermostats these keep only the boiler's own frost protection running and stop the room thermostat calling for heat. If you're not sure what yours does, ignore it and set the thermostat low instead.
What temperature should you set?
• Scottish Water suggests 10°C as a frost-prevention setting, with the programmer on constant (24 hours).
• Insurers often ask for more. Many home insurance policies have conditions for empty homes in winter, and a common one is keeping the heating at a set minimum — often between 13°C and 15°C.
Our advice: set the room thermostat to about 12–15°C, and if your insurance policy names a figure, use theirs. At that setting the heating only comes on when the house drops below it, so it costs far less than you'd think — and much less than a burst pipe.
Before you leave: a checklist
Test the stopcock before the day you go. Old stopcocks are often stiff. If yours won't turn, don't force it — get it looked at before you travel, not when you're packing the car.
Check the boiler pressure. With the heating cold, most combis sit between 1 and 1.5 bar. If it's well below that, top it up, or get it checked before you go. You won't be there to top it up if it drops.
Set the thermostat low and the heating to constant, as above. Don't switch the boiler off at the wall — it needs electricity as well as gas to run.
Top up prepayment meters. If you're on a prepayment meter for gas or electricity, make sure there's enough credit to last the whole trip, plus a cold snap.
Leave a key with someone you trust, and ask them to look in if the weather turns properly cold. Some insurers expect an empty home to be checked regularly.
Check your insurance policy for any rules about how long the house can be empty and what temperature it has to be kept at.
The one that catches people out in Scotland: a frozen condensate pipe
Modern condensing boilers produce water, which drains away through a plastic pipe — usually out through the wall to a drain outside. In a hard frost, that pipe can freeze. When it does, the boiler can't drain, so it locks itself out and shows a fault.
And once it's locked out, nothing is keeping your pipes warm. No heating, no frost protection, for however long you're away.
Before you go:
• Look at where the condensate pipe runs outside. If it's a long, thin, exposed run, it's the kind that freezes. Insulating it, or having it rerouted or upsized, is a small job.
• If a cold snap is forecast while you're away, ask your key holder to check the boiler is still running and isn't showing a fault.
• A smart thermostat that sends an alert when the house temperature drops is worth having if you travel in winter.
• A boiler service before winter checks the condensate trap and the parts most likely to cause a lockout — worth doing if yours is due.
When you should drain down instead?
For a few weeks away, heating on low and water off is the right approach. Draining down is a different job, for a house that will be empty for the whole winter, or one where the heating won't be left on at all. Scottish Water's advice for a property left vacant over the winter months is to turn the water off and drain the system.
Draining a heating system properly — and refilling, venting and re-dosing it with inhibitor afterwards — is a job for a heating engineer. If that's your situation, get in touch and we'll talk you through it.
If you come home to a problem
A frozen pipe: turn off the stopcock if it isn't already, and open the cold taps to let the system drain. Never use a naked flame to thaw a pipe. Warm it gently with a hairdryer or hot water bottle, or call a plumber.
The boiler isn't working: check the display for a fault code and look at the pressure gauge. If the condensate pipe outside is frozen, pouring warm (not boiling) water over it can free it, and a reset may bring the boiler back. If it won't come back on, we start with a fixed Diagnostic Fee — £75 Monday to Friday, 8am to 5pm, or £120 for evenings, weekends and bank holidays — and you get a clear price for the repair before any work starts. See how boiler repairs work → https://www.epicboilers.com/boiler-repair
Gas Safe registered, Reg. 974235.
Sources: Scottish Water — advice on frozen or burst pipes;
Ideal Heating — will turning my water off affect my boiler?
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