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10 common boiler problems

Your boiler is one of the most important and hard-working appliances in your home, and you probably don’t give it a second’s thought until it’s on the blink. Whilst it’s frustrating when your boiler runs into a problem, it’s not always a big deal. And there’s not necessarily something wrong with the boiler itself, it could indicate problems with its fuel supply or a frozen or burst pipe. We’ve put together this quick guide of some of the most common boiler problems and what needs to be done about them.

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10 common boiler problems…

Your boiler is one of the most important and hard-working appliances in your home, and you probably don’t give it a second’s thought until it’s on the blink.

Whilst it’s frustrating when your boiler runs into a problem, it’s not always a big deal.

And there’s not necessarily something wrong with the boiler itself, it could indicate problems with its fuel supply or a frozen or burst pipe.

One way you might be able to tell what’s wrong with your boiler, is if it’s displaying a fault code.

All boilers display error codes differently, so depending on your model, the error code itself will vary, so you’ll need to check your boiler’s operation manual.

If you’re in any doubt about what’s going on with your boiler, you should always contact a Gas Safe engineer for advice.

Remember that most problems can be avoided with proper boiler maintenance, including an annual service.

According to Which? an average of 18% of boilers in UK homes break down every year with the majority facing substantial repair costs due to not adequately maintaining their system.

We’ve put together this quick guide of some of the most common boiler problems and what needs to be done about them. Some small problems can be handled by yourself…

1.   Common boiler problem: You have no heating or hot water

The dreaded no heating or hot water scenario is probably your biggest fear when it comes to boiler problems, and you’re not alone. Nobody wants to be without heating or hot water, particularly in the winter months.

There are three possible scenarios here:

You have no heating and no hot water at all

This is the worst-case scenario because you’ve got the double whammy of a cold house and cold water.

If you’ve got a system or a heat-only boiler and you have an additional immersion heater, you’ll be able to get hot water while the issue with your boiler is being fixed.

Unfortunately, you’ll have no such luck here if yours is a combi boiler.

There are lots of possible explanations for why your heating and hot water has gone off. The simplest things to check first are:

  • Is your boiler displaying a fault code?
  • Have you got an issue with your power; water; or fuel supply?
  • Is the condensate pipe frozen? (more on this later)
  • Is the pilot light on? (more on this later)
  • Is the boiler pressure too low? (more on this later)
  • Is your timer or thermostat working?

If none the above applies, it’s time to call out an engineer because there may be a component failure, such as a broken diaphragm or valve.

Your hot water’s working, but there’s no heating

If you can have a hot bath or shower, but your heating isn’t working, you should start by checking whether all your radiators are hot.

If some of your radiators are hot, or are hot in places, you might need to bleed them or get a power flush to rid them of sludge.

We look at this later. If all your radiators are cold, your boiler might have a broken diverter valve or pump.


Your heating is working, but there’s no hot water

If your home is warm and cosy, but you’re only getting cold water out of your taps, then you have an issue with your hot water supply.

The first thing to do is check that it’s not a problem with an individual showerhead or tap, by checking all your hot taps. If you get sputtering, there could be an airlock in the pipes.

Otherwise, the most likely cause is a broken diverter valve, in which case, you’ll need to call in an engineer.

2.   Common boiler problem: Your radiators aren’t getting hot or have cold spots

If you’ve got cold radiators, this could indicate a need to bleed them, or that you need a power flush.

You need to bleed your radiators

If you’ve noticed that your radiators are cold or have cold spots; or are making funny noises; this might indicate that air is trapped inside them, and needs to be released.

The good news is that releasing the trapped air, or ‘bleeding’ your radiators is a relatively straightforward task that you can do yourself.

It’s usually easy to determine whether your radiators need bleeding. You just need to use your hand to check the temperature of your radiators, from the top to the bottom of each.

Since air rises, it is quite common for the top of a radiator to be cold, and the bottom to be hot, if it needs to be bled.

To bleed your radiators, you need to use your radiator key to open the bleed valve on your radiator. You should hear a hissing sound as the air escapes.

Keep releasing air from the valve until you can no longer hear air escaping and some water begins to trickle out.

You need a power flush

Statistics from BEISAnother potential cause of your cold radiators is that they are being blocked by sludge.

Sludge is a muddy substance made up of rust, dirt and debris which collects over time in your pipes and radiators.

This plays havoc with the efficiency of your heating system, causing corrosion and blockages. This issue can be solved with a power flush.

A power flush is a cleansing process which cleans your entire central heating system, removing the sludge, which would otherwise cause damage and reduce efficiency. 

So, if when you bleed your radiators, the water is discoloured, or no water escapes at all, this may signal the need for a power flush.

3.   Common boiler problem: Your boiler is losing pressure

If you’ve been experiencing boiler problems such as a lack of hot water, it could be that low pressure in your boiler is to blame.

The good news is that low pressure is usually easy to spot, and, in some cases, you can address it yourself.

If you find that your pressure gauge is below one bar of pressure, adjusting this to 1.5 should solve your problem in the short term.

To top up the water pressure in your boiler you’ll need to switch off your boiler and allow it to cool.

Then, you’ll need to check that both ends of the filling loop are securely attached, before opening both valves.

Once the pressure gauge reads 1.5 bar, close both valves, one after the other. You can then switch the boiler back on and, if needed, press the reset button.

There are lots of possible reasons for your low-pressure fault.

If you notice your pressure gauge drops overnight, this could be caused by a leak in your system; a problem with the pressure relief valve; air in your radiators; or a problem with the expansion vessel.

Depending on what the cause is, you may need to talk to a Gas Safe engineer so that the issue doesn’t recur.

4.   Common boiler problem: Your boiler’s condensate pipe has frozen

A diagram of a condensate pipeIf your boiler has stopped working when it’s freezing outside, there’s a chance that your boiler’s condensate pipe has frozen.

Other telltale signs of this issue are if you hear a gurgling sound coming from your boiler or your boiler is displaying an error code “EA”.

All boilers have a condensate pipe. Its job is to take waste from your boiler out into a drain.

If it gets blocked with ice, your boiler will automatically shut down as a safety measure until it’s resolved. Luckily, this isn’t a big problem, and you can fix it yourself quite easily.

To find your condensate pipe, you need to look for a white plastic pipe that comes out of the wall directly behind your boiler.

Check that it runs from the boiler to an exterior drain. Once you’ve found it, and checked that it is indeed frozen, get your kettle on.

Once you’ve boiled your kettle, let the water cool for about 15 minutes, before pouring it down the length of the pipe until the ice has thawed. The final step is to reset your boiler and check that it is working properly.

5.   Common boiler problem: Your boiler’s pilot light keeps going out

The pilot light in a boiler is crucial because it ignites the fuel (usually gas) that heats the water inside the boiler.

It needs to stay lit all the time so that your boiler can operate whenever heat or hot water is required. If it goes out, you’ll have no heating or hot water.

The good news is that you can relight your pilot light quite easily. But if it keeps going out – after you’ve eliminated draughts – there may be a bigger problem afoot.

To relight your pilot light, you’ll need to follow the instructions in your boiler’s operation manual.

Newer boilers will have an ignitor, whereas an older boiler pilot light may require you to light a match for ignition.

If the pilot light keeps going out on a boiler that could indicate that the thermocouple is faulty or broken and requires replacing.

6.   Common boiler problem: You have leaks

Leaking or dripping water is a real pain because it can cause damage to your home, as well as causing problems with the electrical components of your boiler.

If you notice water coming from your system’s pipes, this could be caused by corrosion or by weakened seals on joints.

If the leak seems to be coming from the boiler itself, this could indicate a problem with an internal component, such as a pressure valve or pump seal. These problems can occur where the pressure in the system has become too high or the seal on the pump has worn out.

Regardless of the cause, a leak should be treated as a serious issue, and you should call a Gas Safe engineer to investigate.

7.     Common boiler problem: Your boiler is making kettling sounds

If you’ve noticed that your boiler is making a strange noise a bit like a kettle boiling – a sort of whistling sound – it’s probably due to a common problem called ‘boiler kettling.’

Despite the rather misleading name, your ‘boiler’ doesn’t actually boil water – or it shouldn’t!

Boiler kettling occurs when the water is heated too quickly and reaches boiling point, causing steam to be generated and air to become trapped. The trapped air makes a whistling noise, like a kettle.

Boiler kettling can be caused by limescale build-up on the heat-exchanger, which slows down the flow of water, causing it to heat up excessively.

A faulty component could also be to blame, as well as the possibility of there being a build-up of sludge in the system. This isn’t a problem that you can fix yourself, you’ll need the help of a heating engineer for this one.

8.   Common boiler problem: Your boiler is making strange noises

If it’s not whistling you’re hearing, but something else, this could indicate a different problem to boiler kettling.

Most modern boilers are whisper quiet, so anything above a low hum isn’t normal. Gurgling; banging; whooshing or droning sounds usually indicate there’s a problem.

Gurgling noises are often a sign of trapped air in the system. Bleeding the radiators might help with this issue. Droning noises are sometimes caused by a faulty pump. Whooshing noises sometimes occurs when debris or dust blocks the air intake pipe or air filters.

But whatever the cause, you’ll want to have your noisy boiler looked at by a Gas Safe engineer.

9.   Common boiler problem: Your boiler isn’t responding to the thermostat

Most people use a thermostat to control their boiler’s heating schedule and the temperature of their central heating. 

At its simplest, a thermostat is a control used to regulate the temperature in your heating system. Once you have set a preferred temperature, your thermostat works to keep your rooms at this desired level.

It works by monitoring the ambient temperature in your room, and then turning your heating on or off to maintain your chosen temperature.

Obviously, if your boiler stops responding to your thermostat, it can cause problems. It might be that your boiler and thermostat are not communicating with one another, or it could be that there’s a faulty component.

To get to the bottom of this issue, you should start with the obvious. Check that your boiler and thermostat have power. It could be as simple as the batteries in your thermostat need changing, or the clocks have recently changed.

Once you’ve eliminated those possibilities, consult the manufacturer instructions for your thermostat. Popular brands are likely to have useful FAQs and troubleshooting advice on their websites.

If your control is quite old, it might be time for a new one if advice from the manufacturer seems to suggest it’s on its last legs.

10. Common boiler problem: Your energy bills are creeping up with no explanation

If you’ve got an older boiler, and have noticed unexplained increases in your energy bills, it might be time to consider a replacement.

As well as older boilers tending to be less efficient to start with, their efficiency can also deteriorate further with age.

And at its simplest, a less efficient boiler will cost you more money to run because they use more energy to heat your home.

The efficiency of your boiler is rated using the ErP scale, running from the most efficient, at A, and least efficient at G.

An A rated boiler has an energy efficiency of 90% or more. The Boiler Plus regulations mean that new combi boilers are at least 92% efficient.

To put this in perspective, an older G rated boiler has an efficiency of 70% or less which means for every £1 you spend on your heating bill you are wasting 30p on lost energy.

So, if you have an old boiler, and ever increasing energy bills, it might be worth discussing whether a new boiler could save you money.

To find our about the gas crisis, and how to save money on your gas bill, read our related blog here.

Tips for preventing problems with your boiler

We hope that you’ve found this trouble shooting guide helpful.

Remember that prevention is better than cure, so the best way to avoid running into problems in the first place, is to have your boiler serviced annually.

An annual service will help you to:

  • Avoid breakdowns;
  • Maximise the lifespan of your boiler;
  • Maintain your boiler’s efficiency to help keep your energy bills low;
  • Ensure it is safe; and
  • Maintain your boiler’s guarantee.

But unfortunately, boilers don’t last forever.

If you’ve noticed your boiler is struggling to do what it used to do; or is breaking down regularly; or is not working at all, you might be wondering whether you should try to repair what you have, or whether the time has come for a replacement.

The Heating People are here to help you find what’s right for you, and your home. Call us today to discuss your options with a boiler replacement.

Useful Links:

Which? report on the cause of boiler breakdowns

Worcester Bosch support: Broken boiler

Boiler Guide – thermostat problems.

Vaillant: Most common boiler problems