Central Heating Not Working? Seven Things to Check

Before calling anyone, work through these seven. They solve a surprising proportion of heating problems and they all cost nothing.

Go through them in order rather than jumping about. Many people find the answer in the first three.

1. Thermostat settings

More call-outs than anyone would like to admit come down to this.

Check it is set to heat or auto rather than off, that the target temperature is above the current room temperature, that the batteries are not flat on a digital thermostat, that the timer is programmed correctly, and that nobody has changed it.

Try turning it fully off and back on. Increase the target by five degrees and see if the boiler responds.

If the display is dim or blank, replace the batteries before anything else. A wireless thermostat with flat batteries cannot tell the boiler to fire, and nothing on the boiler itself will look wrong.

2. Boiler pressure

Low pressure is one of the most common reasons a heating system does nothing.

The gauge should read 1.0 to 1.5 bar, usually a green zone. Below 1.0 and the boiler will not fire. Above 2.0 is too high, and is usually marked in red as well. If it is that high with the system cold, bleeding a radiator lets a little water out and brings it down.

To top up: turn the boiler off, find the filling loop, open both valves slowly, watch the gauge rise to 1.0 to 1.5 bar, close both valves firmly, and turn the boiler back on.

The filling loop is usually a flexible hose with a valve at each end, under the boiler. Some boilers have a built-in filling lever or key instead, and the manual shows where it is.

If it needs doing frequently, you have a leak. Topping up treats the symptom. Leak detection finds the cause, and our guide to a boiler losing pressure covers the usual suspects.

3. Pilot light, on older boilers

Only applies to older boilers, since modern ones use electronic ignition.

Look through the viewing window, without removing the casing, for a small blue flame. If it is out, the boiler will not fire.

If you smell gas at any point, do not attempt to relight. Open windows, leave, and call 0800 111 999.

If there is no smell of gas, follow the relighting instructions in the manufacturer’s user manual exactly. On some boilers they are also on a label inside the front flap. It usually involves holding down a button while pressing a spark igniter, and the flame should stay lit when you release the button. Do not remove any panels to get at the burner.

If it will not light, or goes out again after a couple of attempts, stop there.

Repeated pilot light failures usually mean a faulty thermocouple or gas valve. Both are jobs for a Gas Safe engineer, and a boiler repair visit will diagnose which it is.

4. Radiator valves

If the boiler is working but individual radiators are cold:

• Thermostatic valves should be turned up, usually numbered 1 to 5
• The lockshield valve at the other end, under a cap, should be open
• Thermostatic valves stick closed. Remove the head and gently tap the pin underneath. A stuck pin is very common and easily missed.

Once the cap is off, a lockshield valve turns with a spanner or a lockshield key. It is set when the system is balanced, so count the turns if you adjust it. That way you can put it back where it was.

If a radiator is still cold once both valves are open, look at where it is cold. Cold at the top means air, and it needs bleeding. Cold at the bottom means sludge inside the radiator, which needs a powerflush rather than a bleed key.

5. Frozen condensate pipe

Extremely common during a cold snap. Modern condensing boilers have an external condensate pipe that freezes.

Signs are the boiler not starting, gurgling sounds, an error code, and the problem beginning when the weather turned.

The condensate pipe is usually white plastic. It leaves the boiler and runs outside to a drain, and the section outside is the part that freezes.

Pour warm, not boiling, water over the frozen section, or wrap a hot water bottle around it. Reset once thawed, and insulate it to stop it happening again. Do that in the autumn, before the first cold snap rather than after it.

6. Power supply

Simple, and frequently overlooked.

At the boiler: is the switch on, is there any display, is there a fused spur nearby that has been switched off.

If there is a display but the boiler has locked out, try the reset button once or twice. If it locks out again, stop resetting it and call an engineer.

At the consumer unit: has the heating circuit tripped, has the RCD tripped. A tripped switch will be in the off position. Reset it once.

If it trips repeatedly, that is an electrical fault. Turn the boiler off and get it looked at rather than resetting it again.

7. Timer and programmer

Especially worth checking after a power cut, since settings often reset.

Verify the current time is right, that a heating schedule is actually programmed, that it is not on holiday mode, and that AM and PM are correct. That last one catches people out constantly.

Set it to constant temporarily to test whether the heating works at all.

Try the boost button too. If boost brings the heating on, the boiler is fine and the problem is in the programming.

When to call

If you have worked through all seven and the heating still does not work, it is time for a Gas Safe engineer.

Immediately for any gas smell, a sounding carbon monoxide alarm, water leaking from the boiler, a burning smell, or loud banging.

Soon for error codes, a boiler that keeps shutting off, a pump that is not running, no hot water, or unusual noises.

If you smell gas, do not operate any switches. Leave the property and call the National Gas Emergency Service on 0800 111 999. If a carbon monoxide alarm goes off, open doors and windows, get everyone out into fresh air, and call the same number.

Preventing the next one

• Annual boiler service, which catches problems before they turn into a breakdown
• Bleed the radiators yearly, which prevents cold spots and keeps the system efficient
• Insulate the condensate pipe before winter
• Check pressure monthly, so a slow leak shows up early
• Replace thermostat batteries before they die, and the programmer’s too if it uses them
• Keep air bricks and flue terminals clear