How to fix your central heating problems

If something unexpected happens with your central heating in winter, like you suddenly lose your hot water, or you have a radiator that refuses to heat up, it can mean a miserable time in a cold house.

And if you're anything like us, you're probably not that confident with your central heating system and wouldn't know what you might be able to fix yourself.

If you have problems with a gas appliance, you should always call a Gas Safe registered engineer (call 0800 408 5500), but some smaller problems (like radiators that aren't heating up properly) can be fixed easily.

Here, a HomeServe expert explains some of the most common central heating problems and what you can do before you make a pricey call to the experts. Plus we've teamed up with Gas Safe Register to give you essential safety advice.

Read on to find out what to do about:

- Cold patches on your radiator (in the top, middle or bottom) - Some radiators hotter than others - Shower hotter at some times than others - Pressure dial low on boiler - No heating or hot water - Boiler making loud noises

Please note: If you can smell gas, always call the national gas emergency number on 0800 111 999.

Problem: I've got cold patches at the top of my radiator

Solution: If the top part of a radiator is cold, this probably means there's air in the system, stopping the radiator filling with water. You'll therefore need to bleed the radiator to release the trapped air.

This is less daunting than it sounds. Firstly, check there's still warm water in the system by touching your radiators and then turn off the central heating. Give the radiator time to cool, then find the bleed valve on the radiator (this is a small valve on the side of radiator near the top).

Put a towel or small bowl beneath the valve to protect your carpet, then turn it 180 degrees anti-clockwise with a bleed key - if you've lost the one that came with your radiator, you can find them in any DIY store.

The radiator will first expel the air trapped in the system, which will let it fill with water. After all the air has been expelled it will start to drip water. When this happens, close the valve. If the central heating system is a sealed system (one without a 'feed and expansion' tank in the loft), check the pressure (there's more advice on how to do this below) and, if necessary, top up as required.

(If you're not sure if you have a feed and expansion system, it's one where you have a tank in the loft that keeps the water in the central heating system at the right level - this is different from your hot water storage cylinder. It will be connected to the central heating system by one pipe, the water mains by another and have a vent pipe that runs to the outside of the house through which water can be vented if the water in the system expands too much).

Problem: I've got cold patches at the bottom of my radiator

Solution: Cold patches at the bottom of a radiator may mean a build-up of scale, rust or sludge is obstructing the flow of water.

If your central heating has an open-vented system (one with a 'feed and expansion' water tank in the loft that keeps the level of water in your central heating system at the same level - this is different to a hot water storage tank) then you can use a heating system sludge remover. This is a chemical you add to the water tank, a bit like drain cleaner. Fernox Central Heating Cleaner, which you can buy online, should work.

However, if you have a non-open vent system, you'll need to flush through the radiators with a hosepipe, which is a job for the experts.

Problem: I've got cold patches in the middle of my radiator

Solution: This may mean rust and sludge are actually blocking the bottom part of the radiator. To clean your radiator you will need to remove it and flush it out. In some cases your radiator will need replacing. This is a major job and you should contact a plumber to carry it out.

Problem: Some of my radiators are hotter than others

Solution: Having one or more radiators that stubbornly refuse to heat up can be enormously frustrating. You should first check the valves on either side of the radiator, which control the flow of water to and through the radiator. Make sure these are both open. The so-called lockshield valve (the smaller valve that controls water reaching the radiator) may also need to be opened further if the radiator is a long way from the boiler or if you find some take longer to warm up in the morning.

If both valves are open, it could be a build-up of limescale, in which case you'll need to descale the system in a similar way to removing sludge as described above. (The radiator's main on / off wheel valve is usually marked with numbers or moves up and down in its fitting. On the opposite side is the lockshield, which is usually covered with a plastic cap. Beneath this is a metal stud that needs to be turned with a spanner. Clockwise is closed.)

Finally, where the cold radiators are in the house can also give you a clue as to what's wrong. If upstairs, it may be a sign that there's not enough water in the system. And if it's only your downstairs radiators, this is a sign that you have a faulty pump. Replacement will require professional help.

Problem: My shower is hotter at some times than others

Solution: There are many reasons why you may end up taking a colder shower than you might prefer. Most simply, if you have a large family, it could be a case of using more water than your tank holds. We use an average of 35-45 litres of hot water per person per day, which doesn't leave much extra capacity if your tank is 200 litres, for instance.

If you have mixer taps, the flow from one could be obstructed. You should descale your shower head by placing it in a bucket with water and vinegar and check that the shower hose isn't twisted or collapsed. You can also remove trapped air in the system by placing the shower hose without the head in the bath and gradually going from the coldest setting to the hottest.

If that doesn't work, it could be something more complicated, such as the thermostatic cartridge in your shower that limits the temperature of the water. You can replace these yourself, but it's advisable to get a professional in.

Problem: The pressure dial is low on my boiler

Solution: The water in combi boilers needs to be at a slight pressure to work, usually between 1 to 2 bar (a mountain bike tyre is about 3 times that). If the pressure gauge shows it's too low, you need to top up the system using the valve on the mains water inlet pipe. This is usually clearly labelled and has a small lever or a slot for a screwdriver. When shut, it will be at right angles to the pipe. Open it gently and keep a careful eye on the pressure dial, shutting it off when the dial is back in the green.

Problem: I've got no hot water and/or no heating

Solution: No heating or hot water in winter can make for a very unhappy time. But should the worst happen, there are few quick things to check before calling out an engineer that could get your boiler back up and running in no time.

Firstly, as obvious as it sounds, check that your boiler is working. Is the power supply on? Is the programmer also on and are the thermostats turned up high enough?

If the pilot light has gone out, relight it by following your manufacturer's manual or the instructions on your boiler. You should then check that you have gas and oil coming into the boiler (you should be able to hear it and if you check your gas meter, it should be ticking over), although a gas supply problem will mean calling your energy company.

You should also check whether the fuse has blown - if there's no electricity going into the boiler (if the switch is on but there's no light for instance). If you think that's the case, it's advisable to use a professional electrical engineer, as the fuse blows to prevent you from electrocuting yourself.

You should also call in an expert if it seems like it's the pump that's broken. You can tell if the fault is with the pump by running a tap and locating the pump (a short, stubby cylinder, usually red, blue, green or silver in colour, by the boiler or water cylinder). Touch it (cautiously). If all is well, it's usually warm and vibrating slightly. If it's cold, that could mean there's no power. If it's very hot, it could be seized up.

Finally, if it's freezing outside and you have a condenser boiler, it could be that the condensate pipe - a white or grey plastic tube that vents water vapour to the outside - has frozen. This is usually indicated with a specific fault light or by gurgling or bubbling sounds from the boiler.

You can defrost this by feeling along the pipe to find the frozen part - it will be colder than the rest of the pipe and usually in an exposed part. Then pour warm water along the length of the pipe or wrap a hot water bottle around the area. Don't use boiling water, as this can crack or damage the pipe.

Problem: My boiler is making loud noises

Solution: Loud noises from the boiler are often a sign of a serious problem. But before calling in help, there are some checks you can carry out yourself.

If the thermostat is set too high it can lead to overheating the water in the boiler, making the noise you hear. Unfortunately, turning the thermostat down may hamper your radiators reaching the right temperature.

If it's not the thermostat set too high, you could need to descale the boiler as described above, as limescale can cause parts of the boiler to overheat.

Finally, is enough water reaching the boiler? Check the feed and expansion tank in the loft to check it's filling properly and that the float valve isn't stuck. If it's cold out, it may even be that the water supply pipe has frozen.

If you discover what looks like a frozen pipe, turn off the water supply immediately at the main stop tap (usually located under the kitchen sink) and stopcock. Make sure to wrap or cover anything close to the frozen area in case the pipe bursts. Now open the tap that's closest to the frozen part of the pipe, and gently thaw the affected area, working from the tap all the way back to the blockage. Use a low heat source, such as a hairdryer or hot water bottle. The melted ice should drip out through the open tap. If you can't access the frozen part of the pipe, or if the pipe bursts, then you will need to call for a tradesman.

Gas safety

Gas Safe Register says: If your gas appliances aren't working properly, it can mean that they're more likely to break down, but also they could cause gas leaks, carbon monoxide poisoning, fires and explosions.

Signs that your gas appliances aren't working properly are:

- The flame on your cooker should be crisp and blue. Lazy yellow or orange flames mean you need to get your cooker checked - Dark staining around or on appliances - Pilot lights that frequently blow out - Increased condensation inside windows - If you're worried your appliances are leaking carbon monoxide, you can find a Gas Safe registered engineer in your area by calling 0800 408 5500.

If you can smell gas, call the national gas emergency number on 0800 111 999.

This advice has been approved by Gas Safe Register