Draining a summer house's water system for winter
The Abimeister team · Updated · 5 min read
A summer house or cottage in Harju county that stands unheated through winter has one weak point: any water left in the pipes, the boiler or the toilet trap will freeze, expand and split the fitting, often in a place you cannot see until spring. Shutting the system down properly takes an hour or two on a dry afternoon and costs nothing but time. This guide covers when to do it, in what order, and where a toilet trap needs antifreeze rather than draining.
When is the right time to shut the system down
Do it before the first night the forecast drops below zero, not after. In Harju county that is usually sometime in October, though some years push into November. Once frost is possible overnight, water sitting in an outdoor or unheated pipe is at risk, and it only takes one cold night to split a fitting.
If the house is used on and off through autumn, treat every visit as possibly the last one for the season. It is far less work to drain the system on a mild day and refill it on your next visit than to deal with a burst pipe in spring.
How to drain the boiler and the water system
Start by switching off the boiler and letting the water inside cool, since draining a hot boiler is unpleasant and can damage the element. Close the stopcock on the incoming supply, usually where the pipe enters the house or by the well pump, so no more water can flow in.
Most boilers have a drain valve near the bottom of the tank, often needing a screwdriver or a small spanner to open. Attach a hose if you can and run it outside or to a floor drain, since a full boiler holds anywhere from thirty to over a hundred litres. Open the valve and let it run until the flow stops, then leave it open over winter.
If the boiler has no obvious drain valve, or the fitting has seized, this is a job worth calling in rather than forcing — a stripped valve or a cracked tank fitting is a bigger repair than the plumbing it was meant to prevent. Plumbing work from 45 € an hour covers exactly this.
Opening every tap and mixer in the house
Once the stopcock is closed and the boiler is draining, go round the house and open every tap, both hot and cold sides, including any outside tap and the shower mixer. Leave them open. This lets air into the pipework so the remaining water can drain down by gravity rather than sitting trapped between two closed points.
Do not forget taps that are easy to overlook: a garden tap on an outside wall, a washing machine's supply valves, a kitchen mixer with a pull-out hose. Each of these can hold a cupful of water that is enough to split a fitting once it freezes.
Clearing the last water out of the pipes with compressed air
Gravity alone rarely empties a pipe completely — low points and dips in the run will hold a slug of water no matter how long you wait. Where you have access to a compressor, even a small one from a hardware shop, connect it to the highest point of the system, one tap or an outlet fitting, and blow through each branch in turn with the far tap open, working from the point nearest the compressor outward.
You will hear the sound change from a wet splutter to a dry hiss once a branch is clear. Do this for the hot and cold sides separately, and for any outside tap or hose bib last, since those sit furthest from the boiler and lowest in the system.
If the house has no compressor and no pipe run you can reach easily, that is not unusual in an older cottage, and it is one of the more common reasons pipes still split even after the taps have been left open. This is the point where a plumber's visit earns its keep.
Protecting the toilet pan and the trap
A toilet's water trap cannot be drained the way a pipe can, since its whole purpose is to hold a standing seal of water that keeps sewer smells out. If that seal freezes and expands, it commonly cracks the porcelain at the base of the pan, which means a full replacement rather than a repair.
Flush the cistern, then bail or sponge out as much water as you can from both the cistern and the pan itself. Pour a cup or two of proper plumbing antifreeze, sold at builders' merchants for exactly this purpose, into the pan so it sits in the trap. Do not use table salt or car antifreeze; car antifreeze is toxic and not meant for a fitting connected to your drinking water system.
If the pan has already cracked from a previous winter, or the cistern's fill valve looks worn, toilet repair and fitting from 60 € per job is a straightforward way to have it sorted before it becomes urgent.
The shutdown sequence, in order
Doing the steps in the wrong order is the most common way an otherwise careful shutdown still leaves water somewhere it should not be. Follow the sequence below and check it off as you go.
Keep the closed stopcock and the open drain valve in mind through spring too — the system stays empty until you deliberately close the valve and refill it, so a first visit in April should start by checking nothing has been left half-open over winter.
- Turn off the boiler and let it cool
- Close the main stopcock on the incoming supply
- Open the boiler's drain valve and empty it fully, leaving it open
- Open every tap and mixer in the house, hot and cold, including outside taps
- Blow out each pipe run with compressed air where you can reach it
- Bail the toilet pan and cistern, then add plumbing antifreeze to the trap
- Leave all taps open and the stopcock closed until you refill the system
Close the stopcock, drain the boiler, open every tap, blow the pipes out with air where you can, and protect the toilet trap with proper antifreeze, in that order.