What’s Wrong With My Boiler?

Repairing a faulty boiler

A faulty boiler means freezing mornings, chilly evenings and bathing in cold water. If your heating system goes on the blink, banish the shivers by understanding what’s gone wrong.

One in five boilers break down every year, and almost half of all new boilers will develop a fault within their first six years. Many of these could have been prevented with some early troubleshooting, preventative maintenance and regular servicing.

Modern boilers will display an error code to tell you what’s gone wrong, but the symptoms of boiler faults are fairly common regardless of the age, condition and manufacturer of your boiler.

All or nothing – No heat or hot water

The fundamental fault – a boiler that provides you with no heat from the central heating system or hot water through your taps is a pretty useless boiler.

There is no single cause for a lack of heat or hot water. But the first thing to check is whether the boiler is receiving power before considering the following potential issues in order to discount the obvious first:

  • Most obviously, check that the thermostat settings are to a level higher than the current room temperature to indicate that the boiler should be providing heat to the radiators;
  • Ascertain whether the fuel is being supplied. Assure yourself that the supplier is still providing gas or that the oil tank is full;
  • Check the pilot light on older boilers (a small flame visible through a window on the boiler) and reignite if necessary. A modern combi boiler will not have a pilot light;
  • Check that the boiler pressure is at the manufacturer’s recommended level (often this is indicated on the pressure gauge);
  • Is the weather sufficiently cold that the condensate pipe has frozen? If so, read on for simple steps to rectify this problem.

On and off – the boiler that locks itself out at random

Boilers have various fail-safes integrated within them that kick in when certain scenarios are enacted for safety reasons.

If your boiler seems to switch itself off at random, the lockout is most commonly due to one of the following reasons:

  • The boiler is losing pressure;
  • The boiler is low on pressure;
  • The thermostat is not operational;
  • The pump is leaking or broken;
  • Valves are closed not allowing water into the system.

One way or another – hot water but no heating (or vice versa)

If you’re getting hot water from the taps but there is no central heating, then there is a problem. Likewise, if the heating is on but water from the hot taps is cold, your boiler has an issue. A lack of one or the other is a common problem, particularly on combi boilers.

The usual culprit on a combi boiler in this situation is the diverter valve.

The diverter valve routes hot water to your taps/showers and to your heating system. In theory, it should prioritise the water to taps and showers when they are turned on. Once you turn these off, it then switches all hot water back to the heating.

As the diverter valve is a moving part, it is common for it to get stuck over time. This is mainly due to a build-up of debris and sludge. When this happens, the valve will either stick on the heating or the hot water system.

You will most often need a heating engineer to replace the faulty diverter valve.

Other causes of this type of problem include a drop in boiler pressure, thermostat problems and broken diaphragms and airlocks.

Getting the needle – low boiler pressure

Boiler pressure is a measurement of the pressure of the hot water passing through the central heating system. If the boiler pressure drops too low then the central heating will fail to work.

Your boiler will feature a gauge that can be used to read the boiler pressure. Typically boiler pressure should sit somewhere between 1 and 2. However, you should consult the manufacturer’s instructions to find the appropriate pressure for your boiler.

All boilers will slowly lose boiler pressure over time, but a sudden sharp drop is often the sign of a bigger problem. If you’ve noticed a rapid drop in boiler pressure check for water leaks and cold patches on radiators (as they may need bleeding).

Increasing boiler pressure is something you can most often do yourself. A persistent loss of pressure when the heating is on almost always indicates a small leak somewhere in the system. A loss in pressure when all are off indicates a larger leak.

Other causes of a sudden drop in pressure include a fault with the Pressure Relief Valve, a broken auto air vent, a faulty expansion vessel, radiators filled with air, or simply a broken pressure gauge itself.

Cold outside – a problem with the condensate pipe

All boilers must be condensing nowadays. Condensing boilers collect acidic water and gases and distribute it to the outside drainage system.

Condensate pipes are often external to the property which makes them prone to freezing. At other times of the year, they can become blocked. Both of these scenarios will often lead to a boiler lockout.

A frozen pipe can be thawed out by pouring hot water over it. A blockage can often be overcome by removing the pipe, flushing warm water through and reinstalling it. You may want to lag the pipe to prevent future freezing.

Causing a commotion – noisy boilers

A heating system will make a number of noises throughout its operation. But if you notice one of the following sounds, it’s best not to ignore it but to assume there may be a fault:

  • Whistling – often caused by a build-up of sludge on the heat exchanger;
  • Banging – often caused by loose components or pipework, or a failing pump;
  • Clanking – often caused by loose pipework or an obstructed boiler fan;
  • Buzzing – often caused by malfunctioning electrical components;
  • Louder than usual humming – often caused by a loose part, particularly the pump;
  • Gurgling – often caused by too much air in the pipes;
  • Kettling – if the noise coming from the boiler sounds like a kettle coming to the boil, the problem is probably caused by sludge and sediment in the central heating system.

Remember, safety must come first with any gas or oil-fired system. If you aren’t confident what the problem is, or that you can fix it yourself, call out a registered engineer. Or you could just make things worse.

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