A heating system sits idle for four or five months and then, on one particular evening, every house in London asks it to work hard at the same time. That is why the first sustained cold snap generates a spike of breakdowns: not because boilers choose that moment to fail, but because that is the moment anyone finds out they already had.
Everything below can be done in September or October. The point of doing it then is not virtue, it is availability — an engineer in October can come this week and can order a part. The same engineer in mid-December is booked, and so is everybody else.
Run the heating now, in the warm, for half an hour
This is the single most valuable thing on the list and it costs nothing. Turn the heating on, set the thermostat high enough that it genuinely calls for heat, and leave it running for half an hour. Then walk round the house and put a hand on every radiator, top and bottom.
What you are looking for is anything that is not uniformly hot: a radiator that stays cold, one that is warm at the top and cold at the bottom, a valve that weeps, a pump that is noisy, a boiler that fires and then shuts down again within a minute. Every one of those is a problem you now have eight weeks to deal with instead of eight hours.
Bleed the radiators, then check the pressure — in that order
Air collects at the top of radiators over a summer of standing still. A radiator that is cold at the top and warm at the bottom has air in it, and bleeding releases it: a bleed key, a cloth, a quarter turn until the hiss becomes water, then close it. Work from the ground floor upwards.
The order matters because bleeding lets water in to replace the air, which lowers the system pressure. Check the gauge after bleeding, not before, and top up if it has fallen below the cold range — usually one to one and a half bar, though your manufacturer's figure governs.
One important distinction: a radiator cold at the BOTTOM and warm at the top is not air. That is settled sludge, and bleeding will do nothing at all for it. It means the system wants cleaning, which is a job worth booking now rather than in January.
- Run the heating for half an hour and feel every radiator, top and bottom
- Bleed from the ground floor up, then check and correct the pressure
- Cold at the top means air; cold at the bottom means sludge
- Book a service in September or October, not in December
Insulate the condensate pipe before it costs you a night
The plastic pipe running out of the bottom of the boiler and down an outside wall carries acidic condensate away, and it is the single largest cause of breakdowns on the first hard frost in London. When it freezes, the boiler cannot discharge and locks out — usually at around four in the morning on the coldest night of the year, along with several thousand others.
Foam lagging designed for external use, fitted along the whole outside run, prevents most of it and costs very little. Where the pipe is long, undersized or running at a shallow fall, the better answer is to reroute it internally to a soil stack, which removes the problem permanently. In converted flats in Brent, Camden and Hackney that reroute is often possible and rarely offered, and it is worth asking about.
Book the service now, and the certificate too if you let
A service before the season is genuinely different from a service in the middle of it. Combustion gets measured, the case seal and flue get inspected, the condensate trap gets cleaned, and anything wearing out gets found while parts are available and diaries are open. A boiler over about ten years old benefits most, because that is where parts availability starts to matter.
If you let property, the same logic applies to the gas safety record with an extra advantage attached: the check may be carried out up to two months before its deadline without moving the renewal date. That turns a fixed deadline into a two-month window you can negotiate with a tenant, and access is almost always the thing that makes these run late. There is no reason to leave it to the last week.
Five minutes on the things that are not the boiler
Test the carbon monoxide alarm and change its batteries. In England an alarm is required in any room used as living accommodation that contains a fixed combustion appliance, and an untested alarm is not an alarm.
Find your internal stopcock and check it actually turns — usually under the kitchen sink. In an emergency the ability to stop the water in ten seconds is worth more than any tool in the house, and a stopcock nobody has moved in fifteen years is often seized.
Lag any exposed pipework in a loft, garage or outhouse. And if you are going away over Christmas, leave the heating on a low setting rather than off: a house held at a low temperature does not freeze, and a burst pipe discovered on your return is a different order of problem from a cold week.