How to Get Your Central Heating Ready for Winter: A Practical Guide for London Homes

Most of us only think about our heating on the first properly cold morning, when the boiler refuses to fire up or the radiators stay stubbornly cold. After months of sitting idle over the summer, heating systems benefit from a little attention in the autumn. The good news is that many of the jobs below take minutes and need very few tools. Work through them now and you will go into winter with a warmer home, lower bills and far less chance of a breakdown.

1. Turn the heating on before you really need it

Run your central heating for around 30 minutes now, while the weather is still mild. Pumps and valves that have not moved since spring can stick, and it is much better to discover a fault in late September than during a frosty week in January, when heating engineers across London are fully booked. While it runs, walk round the house and feel every radiator.

2. Bleed any radiators that are cold at the top

A radiator that is warm at the bottom but cold at the top usually has trapped air inside. To bleed it:

• Switch the heating off and let the radiators cool down.
• Hold an old cloth under the bleed valve at the top corner of the radiator.
• Use a radiator key to open the valve about a quarter of a turn. You will hear air hissing out.
• Close the valve as soon as water starts to appear.

Start with the radiator furthest from the boiler on the ground floor and work your way round. Radiator keys cost very little and we keep them in stock at our trade counter.

3. Check your boiler pressure

If you have a combi or system boiler, it will have a pressure gauge on the front. Bleeding radiators lets a little water out, so the pressure often drops afterwards. Most boilers like to sit at roughly 1 to 1.5 bar when the system is cold, but always check your manufacturer's manual for the correct figure. You can top it up using the filling loop underneath the boiler. If the pressure keeps falling week after week, you may have a leak somewhere and it is worth calling a heating engineer.

4. Look out for cold patches at the bottom of radiators

Cold spots at the bottom or in the middle of a radiator are a sign of sludge. This black sludge, known as magnetite, builds up as the inside of your pipes and radiators slowly corrodes. It restricts the flow of hot water, makes your boiler work harder and can eventually damage the pump and heat exchanger.

A heating engineer can clean the system using a chemical cleaner or a power flush. Once the system is clean, two products help to keep it that way:

• Central heating inhibitor, such as Sentinel X100, which is added to the water to protect metal parts from corrosion.
• A magnetic filter, such as a MagnaClean, which is fitted on the pipework near the boiler and catches debris before it can do any harm.

5. Protect your system from London's hard water

London and much of the South East has very hard water. Every time water is heated, some of the minerals it carries are left behind as limescale. Inside a combi boiler, limescale coats the heat exchanger and can lead to noisy operation, slow hot water and reduced efficiency. A scale reducer fitted on the cold mains supply to the boiler is a sensible addition in our area, and many boiler manufacturers recommend one for hard water regions.

6. Check your thermostat, timer and radiator valves

Thermostatic radiator valves (TRVs) can stick in the closed position after a long summer. If a radiator stays cold even though the rest of the house is warm, take the head off the valve and gently press the small pin underneath. If it is stuck, a few careful taps usually free it.

It is also a good moment to check your programmer. The clocks go back on Sunday 25 October 2026, so make sure your heating schedule still matches the times you are actually at home.

7. Consider lowering your boiler flow temperature

Modern condensing boilers work most efficiently when the water returning to them is cool enough for them to condense. Many combi boilers are left set to a high flow temperature, which stops this from happening. Turning the radiator flow temperature down to around 60°C can help your boiler run more efficiently while still keeping most homes comfortable. Your rooms may take a little longer to warm up, so you may want to adjust your timer. If you have a hot water cylinder, speak to your heating engineer before making changes, as stored hot water needs to be kept at a safe temperature.

8. Insulate exposed pipes

Pipes running through lofts, garages, cellars and outside walls are the most likely to freeze. Foam pipe insulation is inexpensive and easy to fit yourself. Pay special attention to the white plastic condensate pipe that runs from a condensing boiler to a drain outside. When it freezes, the boiler shuts down, and it is one of the most common causes of winter call outs. Lagging the outdoor section, or having it rerouted internally where possible, can prevent the problem.

9. Book your annual boiler service

An annual service by a Gas Safe registered engineer keeps your boiler running safely and efficiently, and is usually a condition of your manufacturer's warranty. Book it early, as diaries fill up quickly once the weather turns. While you are at it, test your carbon monoxide alarm, or fit one if you do not already have one near the boiler.

10. Replace radiators that are past their best

If a radiator is badly rusted, leaking or still cold after bleeding and cleaning, replacement is often the best option. Modern radiators and towel radiators heat up quickly and come in a wide range of sizes, so upgrading is a good opportunity to improve both comfort and style. Our heat loss calculators can help you work out the right output for each room.

How Precise Supplies can help

Whether you are a homeowner tackling a few jobs yourself or a heating engineer stocking the van for the busy season, our team in Wimbledon can help. We stock radiators, towel radiators, inhibitors, magnetic filters, scale reducers, pipe insulation, valves and spare parts from trusted brands including Worcester Bosch, Sentinel, MagnaClean, Kartell K Rad, Eastbrook and Armaflex.

Visit our trade counter at Unit 17, Windsor Park Industrial Estate, Wimbledon, London SW19 2TJ. We are open Monday to Friday from 7am to 5pm and Saturday from 8am to 1pm. You can also order online for click and collect, or take advantage of free delivery on orders over £150. Not sure what you need? Call us on 0208 143 4192 and we will be happy to give you some expert advice.