Gas Central Heating Problems

Get to the bottom of the trouble when your home's heating loses its health.

Find the answers you need in the following common problem categories. Also see our video on Troubleshooting Central Heating Problems. You can also troubleshoot boiler problems using our Appliance Fault Advisor.

It's important to know that unless you're a trained professional, DIY on gas appliances is out. Simply put, carbon monoxide is dangerous, so think GSI (Get-Someone-In) for your own safety. All gas engineers must be approved by the Gas Safe Register* to carry out safe gas repairs.

To keep boiler breakdowns at bay, it's a good idea to look into Annual Boiler Servicing. Whether you have a Gas Boiler, Oil Boiler or Solid Fuel Boiler; when it comes to heating repairs prevention is definitely cheaper than cure. Also see Bleeding Radiators and Gas Boiler Maintenance to learn more about keeping your boiler in good condition.

Central heating troubles can be tricky to solve because the problem could be a number of things that only a professional should tackle. If in doubt, call in a Gas Safe Register* approved Heating Engineer for a safe repair.

To protect your home against sudden problems that can hit the pocket hard, you might like to choose Gas Boiler Cover or Central Heating Cover.

Choose from the following list to find the advice your looking for:

• Complete Loss of Heating / No Hot Water
• Partial Loss of Heating
• Noisy Boiler
• Boiler Failure
• Faulty Boiler Controls
• Leaking Boiler Pipes
• Cold Radiator
• Leaking Radiator
• Leaking Boiler

Complete Loss of Heating / No Hot Water

To isolate your heating problem, check the following:

1. Power supply on at the mains? Contact your Electrical Supplier if not.
2. Boiler gas supply fine? When the gas Stopcock is on but no gas is coming through, you have a gas supply problem and need to call you Gas Supplier. In the case of Oil Boilers, check there's enough oil in the tank by reading the Gauge.
3. Pilot Light igniting? If your boiler's Pilot Light won't ignite, you either have a gas supply problem (contact your Gas Supplier) or you'll need to call in a Gas Safe Register* approved engineer for a repair.
4. Central heating programmer in the 'on' position and thermostats are turned up high enough?
5. Central heating pressure correct? Check its set to the manufacturer's instructions (generally 1 bar). If it is, either you have a gas supply problem (contact your gas supplier) or you'll need call in a Gas Safe Register* professional.

Partial Loss of Heating

1. First, turn off the central heating at the main controls.
2. You will need to Bleed your Radiator so that the trapped air can be released. The Air Release Point or valve normally has a small red handle and is located on the side of each radiator. Open it with a radiator key (found at most DIY stores).
3. There will be a hissing sound as the air escapes.
4. As soon as the water begins to flow, close the air vent.
5. Switch your central heating back on.
6. If your radiator is cold at the bottom, this indicates a build up of rust and sludge. If your central heating has an Open-Vented System, you can use a heating system sludge remover, which can be bought at most DIY stores. Add the liquid to the feed and expansion tank. After a few days, you will then need to empty and refill the system. Non-open vent systems require you to flush through the radiators with a hosepipe.

Noisy Boiler

Hissing or banging noises from your boiler or heating pipes are caused by the following:

Scale in the Heating System

The build up of scale can be treated with a chemical descaler, found at most DIY stores. This involves shutting down the system, adding the product and leaving it to work for a few days. The system then needs to be drained, flushed through and refilled.

This can cause 'hot spots' which produce loud bangs from steam bubbles. This can be treated by adding a chemical descaler to the Feed and Expansion Tank, found at most DIY stores. The system then needs to be drained, flushed through and refilled. See Bleeding Radiators for help with this.

Boiler Thermostat is Set Too High or is Faulty

See Faulty Boiler Controls.

Lack of Water or Pressure in the Central Heating System

You will need to double check that the mains water is on. If it is, first turn off your boiler and check your Feed and Expansion Tank - move its metal arm to release the Float valve if it's stuck. Check that the Open Safety-Vent Pipe is correctly installed. Another cause could be that you have Burst of Frozen Pipes.

If the problem is a lack of water pressure, the pressure indicator on your central heating boiler will usually indicate it needs to be increased.

Boiler Failure

1. If your boiler won't turn on, the problem could be with its Pilot Light . Check whether the gas Stopcock is open. If no, turning it on will solve the problem by restoring gas supply. If yes, you'll need to call in a Gas Safe Register* approved professional for a repair.
2. When there's no gas coming through the gas stopcock, you have a gas supply problem and need to call your Gas Supplier.
3. If your boiler model doesn't have a pilot light, press the deblocking button. If that doesn't work, check the central heating pressure is set to the manufacturer's instructions (generally 1 bar).
4. If the central heating pressure is correct, either you have a gas supply problem (contact your gas supplier) or you'll need to get a Gas Safe Register* approved engineer in for a repair.
5. If your boiler only works (provides hot water) when the central heating is on, you'll need to call in a Gas Safe Register* approved professional.
6. To keep any further boiler breakdowns at bay, it's a good idea to look into Annual Boiler Servicing - when it comes to heating repairs prevention is definitely cheaper than cure. See Bleeding Radiators and Gas Boiler Maintenance to learn more about preventing problems.
7. If you rent your property and want full peace of mind, ask your landlord about the Annual CP12 Certificate. By law, he/she should give you a copy of the gas safety check on your home's boiler every year.

Faulty Boiler Controls

Boilers have a series of control mechanisms designed to distribute heat and hot water at peak times. Faults with these controls can run up your fuel bills and make your home uncomfortably hot or cold. Try the following:

Thermostats

Check the age of your thermostat. Over time they can lose their accuracy, misreading temperature settings and turning the heat on/off at incorrect times. While a gas boiler engineer can clean and recalibrate your old thermostat, it might be wise to purchase a new one at your local DIY store. Most new thermostats also include good energy-saving controls to warm your house when you need it and turn the heat down when you don't. This can cut your heating bills by 10-20%.

Programmers & Time Switches

These are time-clock driven. Check that the clock dial isn't stuck or the program on/off timing will be wrong. The hot water and heating are controllable via the timer switches found on your boiler.

Electronic Programmers

Check that the LCD display, circuit board electronics or Relay hasn't failed. If you need to replace the programmer, make sure the new one has what's called a Universal Backplate - this allows any further replacements to be as simple as plugging in a the new programmer without needing to call in a professional.

Radiator Valve

If you have a Thermostatic Radiator Valve on your radiator, adjust it the heat you need. Or, if you have a conventional Lockshield Valve, remove the plastic cover and adjust the setting using the right tool (these can be found at most DIY stores). If no change occurs after you've adjusted the settings, you have a fault with your Radiator Valve and are best advised to call in a professional to drain the system and replace it.

Leaking Boiler Pipes

Try the following steps:

1. Identify where the leak is coming from. Most leaking Pipe Joints have Compression Fittings that can be repaired using a spanner or wrench. Tighten the joint slightly, no more than a quarter turn. If this doesn't stop the leak, don't tighten it any further as this will damage the joint.
2. Isolate the area by closing the valves on each side of the boiler or alternatively drain the system to below the leak.
3. Undo the nut on the joint and pull out the pipe slightly. Wrap two or three turns of PTFE tape around the face of the Olive where it meets the joint. Tighten the nut.

Cold Radiator

For a cold radiator problem, try the following checklist:

1. Boiler gas supply on? When the gas Stopcock is on but no gas is coming through, you have a gas supply problem and need to call you Gas Supplier. In the case of Oil Boilers, check there's enough oil in the tank by reading the Gauge.
2. Pilot Light igniting? If your boiler's Pilot Light won't ignite, you either have a gas supply problem (contact your Gas Supplier) or you'll need to call in a Gas Safe Register* approved engineer for a repair.
3. Central heating programmer in the 'on' position and thermostats are turned up high enough?
4. Build-up of rust or sludge? A cold patch at the bottom of the radiator means you need to flush it out. If your central heating has an Open-Vented System, you can use a heating system sludge remover, which can be bought at most DIY stores. Add the liquid to the feed and expansion tank. After a few days, you will then need to empty and refill the system. Non-open vent systems require you to flush through the radiators with a hosepipe.

Also see our video on Troubleshooting Cold Radiators.

If one radiator isn't warming up, solving the problem depends on where it's located:

Upstairs Radiator

This is an indication that the Feed and Expansion Tank in your loft has run dry. This usually points to a larger problem. Also check the ball valve in the tank isn't blocked or jammed. Try the following:

1. Clear any obstructions to the ball valve.
2. Refill the cistern, making sure there is enough room for the water to expand when the system heats up. When the system is cold, there should be just enough water to make the ball float and switch off the water coming in.

Downstairs Radiator

This is an indication that the pump is faulty. Replacement will require a Gas Safe Register* approved engineer.

When Radiators are Cooler in One Area of the House

When the radiators closest to the boiler are hotter than those further away, it means you have a Balancing problem. Try using the Lockshield Valve on each radiator to regulate the flow of water into them. By partial closing of these valves, the radiators nearest the pump can be restricted more than those further away.

Leaking Radiator

This indicates internal corrosion. One of the most common causes of a pinhole leak (a small jet of water from the body of the radiator) is corrosion that can occur within a few weeks of the system being fitted because the debris that collects during installation hasn't been properly removed. It can also occur because of air being drawn in. Try the following:

1. Turn off the valves at each end to relieve the pressure.
2. Remove the Radiator and leave the rest of the system running.
3. Flush out the system using a non-acidic cleaner.
4. Refit the radiator.

Leaking Boiler

This is a fairly common problem. Causes can range from a crack in one of the boiler's cast iron (or aluminium) sections to a broken seal on the boiler's Circulation Pump. First you need to isolate the source of the leak - this can be tricky to do so we recommend you call in a Gas Safe Register* approved professional.