Central Heating Not Working: Check These Fixes for Common Boiler Problems

If you are having issues with your central heating or your boiler, this is the guide for you. In it, we explain the 14 most common problems that you will encounter with your heating or boiler and tell you how to fix them. It will only take you 5 minutes to read but it could save you a fortune in call out charges and repair bills.

Central heating and boilers always go wrong at the worst possible time. This tends to panic people and can mean you end up spending money you don’t need to on engineers and repairs.

In this guide, we are going to help settle the nerves by explaining some of the most common problems that can arise with a central heating or boiler system.

We will explain the issue in simple language that anyone can understand. Then we will recommend the best course of action to fix the issue.

This guide covers all major boiler brands including Ariston, Baxi, Glow-Worm, Halstead, Ideal, Vaillant and Worcester Bosch. So, no matter what boiler you have, you can be confident that we will help you solve your problem.

Safety Note Regarding Boiler Problems And Repairs

While this guide should offer some clarity on what your boiler or central heating problem might be, it is important to remember that boilers are potentially very dangerous things and if you are in any doubt at all, you should always contact a qualified Gas Safe engineer.

They will be able to help you determine if the problem is serious or something more minor. They should also be able to outline the best method to fix it.

In some cases, you might find that buying a new boiler is a cheaper and more practical option than repairing your existing boiler.

If this is the case, your local tradesperson will offer you a quote to do this, but we would also strongly advise you to take a look at WARMZILLA too.

WARMZILLA is an online boiler sales and installation service that offer extremely competitive prices on a whole range of different boilers. Visit their website today and fill in their short form to get a no-obligation fixed-price quote.

It only takes two minutes and you don’t have to enter any personal information. WARMZILLA will be able to offer you a great range of boilers, at great prices, with competitive installation costs and some great extras, like extended warranties, thrown in too.

If a new boiler is what you need, you must make WARMZILLA one of the places you go to for a quote.

Top 14 Heating and Boiler Problems

In the following section, we will outline the 14 most common boiler and central heating problems and recommend the best way to fix them.

If none of these sound like your problem, feel free to leave a comment at the bottom of the page outlining what is happening for you. We will try to respond to all new queries as quickly as we can.

#1: Boiler Switching Off By Itself

It is not unusual for any type of boiler to automatically switch itself off. This is a problem that can happen every few days, every few hours, every few minutes, or even every few seconds.

The reason boiler’s switch themselves off is usually because some sort of failsafe has kicked in. If something happens in your boiler that could potentially be dangerous, a boiler lockout is implemented. This shuts the boiler down.

If you are not aware of any potential issue, it can appear that the boiler is randomly switching itself off. In reality, it is likely that one of the following issues is happening:

  1. The boiler is losing pressure.
  2. The boiler is low on pressure.
  3. The pump is leaking or broken.
  4. The thermostat is broken.
  5. Valves are closed not allowing water into the system.

If this is happening on a regular basis, it is advisable to get a qualified central heating engineer to look at your boiler. It could be something very simple that can be fixed by tweaking the settings or making a small adjustment. But it could be something much more serious.

#2: Boiler is Losing Pressure

A loss of pressure is a common boiler issue and is usually caused by a leak somewhere in either the boiler itself or your central heating system.

It is possible that you might be able to see the source of the leak if you check the pipes around your boiler or those visible pipes in your central heating system, such as those feeding radiators and towel rails.

Depending on the size of the leak, your boiler pressure might drop very slowly or more quickly. If a small leak is the problem, the pressure will generally drop more when your boiler is switched on. If it is a larger leak, the drop in pressure will be seen regardless of whether the boiler is on or off.

A fast drop is generally a more serious problem. If your boiler’s pressure gauge drops overnight, the cause is likely to be one of the following things:

  1. You have a leak.
  2. Your boiler’s pressure relief valve (PRV) is not working properly.
  3. Your boiler’s auto air vent is broken and leaking pressure.
  4. Your radiators are full of air and need bleeding
  5. The boiler’s expansion vessel has a problem.
  6. Old joints in your boiler or pipework are degrading and leaking.
  7. The pressure gauge on your boiler isn’t working.

While you could buy some leak sealant and fix the problem yourself, if you are in any doubt, it is best to check with a trained engineer. Don’t fiddle with the pressure too much yourself as there is a risk that the whole boiler could explode.

#3: The Boiler Constantly Leaks

If there is constantly water leaking out of your boiler, it can be very disconcerting. But actually, such leaks are usually superficial and unlikely to cause any long-term damage to either your boiler or your home.

But, if the water manages to leak onto the electrics, especially the printed circuit board (PCB) in your boiler, this is a major issue and will likely cost you between £400 and £500 to fix.

Most boiler leaks are as a result of one of the following things:

  1. The heating pump is not secure in the boiler.
  2. The heating pump has blown a seal or a gasket.
  3. The expansion vessel diaphragm has degraded.
  4. Your boiler has a cracked heat exchanger.
  5. Water is getting into your boiler down the flue when it rains.
  6. Your boiler’s filling loop is leaking.
  7. Pipework connected to your boiler is either installed incorrectly or not soldered properly.
  8. Your boiler’s pressure release valve has failed.
  9. Internal parts in your boiler have corroded and are now leaking.

Unless you can see that the leak is coming from a pipe underneath the boiler that simply needs tightening up, it is best to get a qualified heating engineer to assess the problem. It might be a simple fix, but it could be something more complicated and in the worst-case scenario, you might possibly need a whole new boiler.

# 4: Boiler Noise

Noisy boilers can be hugely annoying but it is a very common issue and can happen in new boilers as well as old ones.

One of the most common reasons your boiler starts to make noises is if the central heating pump develops a fault. It is quite common for air to build-up in these pumps which causes an airlock.

This problem is easy to fix and is something you can do yourself if you have a more modern boiler. All you have to do is locate the pump by removing the boiler casing. You will find a small bleed screw on it.

Just open this slightly and you will hear a hissing noise. Once the hissing noise stops and a little water comes out, close it again and the problem should be fixed. It is just like bleeding a radiator.

# 5: Boiler Makes a Loud Bang When Starting Up

Loud bangs are never a good thing, so it is understandable if your boiler makes a loud bang before it starts, you will be worried.

It will sound a little like a small explosion and that’s because it probably is exactly that. This problem is usually caused by excess gas in the chamber which causes your boiler to ignite more gas than it needs to.

Sometimes, when you get the noise, the boiler will still light on the second or third attempt. Other times, it will not light at all and is likely to lockout after the third attempt.

The problem can usually be resolved by replacing the ignition burner. This is a small component that can wear out over time. Your central heating engineer will be able to replace it quite easily and without any great expense too.

# 6: Heating Works But No Hot Water (or vice versa)

This can be one of the most confusing issues with a boiler when it is providing you with one service but not the other. It is also remarkably common. The culprit is usually one component; the diverter valve.

A diverter valve is the part of your boiler that filters hot water to your taps, showers, radiators and towel rails.

Its focus is usually taps and showers and once these are switched off, it will concentrate on your radiators. But this valve can get stuck which stops it from sending hot water to one thing or the other.

The cause of this issue is almost always a build-up of debris and sludge in your system. Sometimes a flush can clear out the system but if you have an older boiler you might need to replace the diverter valve.

This is a big job and it is quite possible that your engineer will recommend replacing the whole boiler rather than just this one component.

If that is what the advice is for you, be sure to take a look at WARMZILLA to see if you can get a high-quality and energy-efficient new boiler for less.

# 7: No Heating or Hot Water

If your boiler is failing to produce either hot water or heating, it is quite likely that the problem has been caused by the motorized control valve. This component can sometimes be referred to as a mid-position or Y-plan valve.

Like the diverter valve mentioned in the previous section, this valve can also get stuck thanks to a build-up of sludge or debris. It can also sometimes just go wrong.

Sometimes, your heating engineer might be able to unblock the valve and fix any minor problems with it. If yours is beyond repair, you will need to get it replaced.

# 8: Radiators Won’t Heat Up

If your boiler is functioning fine but your radiators still won’t heat up, the good news is that the problem is probably both simple and not to do with your boiler.

The most common cause is air in your radiators, so before you try anything else, go round and bleed all of your radiators and towel rails to make sure there is no air trapped in the system.

If the problem persists, the most likely culprit is your central heating pump. These pumps can be prone to seizing, especially as they get older. Often this can be fixed by locating the pump behind your boilers front panel and giving it a gentle tap.

If this does work, the problem is resolved in the short term, but it is likely to recur. If it does, you will probably need to think about replacing the pump.

We would recommend consulting your heating engineer at this point. It could be that the issue is caused by a build-up of sludge and debris in the system. If this is the case, a system flush might solve the problem.

# 9: Water is Far Too Hot

If you are finding that your hot water is much too hot, it is likely that there is a problem with your thermostat.

The thermostat controls the temperature of the water. If it thinks the water is cooler than it actually is, you will find your hot water is too hot.

Different central heating systems have different types of thermostats that can go wrong. The most common problem is with a cylinder thermostat as this is most frequently found on systems that have cylinders.

These thermostats can be easily replaced without incurring great expense.

If the water that is too hot is coming from your shower, it is likely that it is not a thermostat that is causing the problem. Rather, the cartridge on your shower is likely to be the problem.

These can also be easily replaced and should solve the problem.

# 10: Boiler Lockouts And Condensation Problems

If your boiler has locked out, there is often an easy way to find out what the problem is. For newer models, the boiler should generate a fault code on the display. Just take a look in your boiler manual (or online) and you should be able to discover which fault the code relates too.

Perhaps the most common cause of a lockout is condensation. All boilers produce condensation from the water and gases they create. This condensation is usually drained away and gases vented out, but if there is a problem with either the condensation pipes or the flue this can cause issues.

These pipes are extremely small and can get blocked quite easily. It is also not uncommon for them to freeze if the weather outside is especially cold.

Freezing is a simple issue to resolve. Just pour some warm water over the pipe and it should melt any ice. You will probably then want to lag the pipe to stop the problem reoccurring.

If something else is causing the blockage, you can remove the pipe and then try to flush hot water through it to remove the blockage. If this doesn’t work, you can buy a replacement pipe at most DIY shops and this is easy to fit.

#11: Radiators Feel Cold at Either the Bottom, Middle or Top

If you are having problems with your radiators, it is important to identify which bit of your radiator is not heating up properly as this is a big indicator of what the problem may be.

One common issue that we are seeing a lot in modern radiators is that the system has not been balanced correctly. This means that the right amount of hot water is not reaching every radiator. It is something your heating engineer should be able to fix without too much trouble.

It is rare that the bottom of your radiator doesn’t heat up but other sections do because gravity causes the water in the radiator to sit at the bottom first. But other sections can have a problem:

Top of Radiators Won’t Heat Up

If the top of your radiators feel cold, it is usually caused by a build-up of air. This can be fixed very easily by bleeding the radiator. Use a bleed key to open the vent and let the air out. As soon as a little water comes out, the air is gone and you can close the vent.

It is advisable to check the whole system while you are bleeding and to go round and bleed again every couple of months or so.

Middle & Top of Radiators Won’t Heat Up

If the top and middle of your radiators is cold, this is more likely to be caused by a build-up of sludge or debris rather than air.

It is important to get this cleared out as if it is left, it can cause problems with your pipes and your boiler. There are a couple of options you can choose to get a sludge build-up sorted:

  1. Hot flush – Your heating engineer will run chemicals through the system at a normal flow rate and pressure which will break down any build-ups.
  2. Power flush – This is a hot flush that is done at a higher pressure. It clears more out but is not advisable in older systems as it can damage pipework.
  3. Replace radiators – If a flush doesn’t work, the next best option is to replace any affected radiators. A new radiator is not that expensive and installation is usually fairly straightforward.

If sludge build-ups are a regular problem, it is a good idea to get a sludge filter fitted after your system has been flushed. This will help to prevent the problem reoccurring. Magnaclean and Fernox are two good brands but your heating engineer will be able to recommend a filter that is suitable for your system.

#12: Boiler Controls Not Working

Problems with the controls on a boiler are far from unusual. These can sometimes appear like other issues but are usually purely electronic issues. It is not very easy to determine if your controls are causing the problem, but there are a number of issues that are likely to be caused by the controls including:

  • Your boiler switching on and off when it’s not meant to.
  • Temperatures appearing to be much hotter or colder than it shows on the thermostat.
  • Thermostat not clicking.
  • Thermostat or mechanical timer buzzing.
  • Radiator valves not increasing or decreasing the temperature according to their setting.
  • Water coming out of taps or showers too hot.

You will need to take advice from your heating engineer on how to resolve this issue but in many cases, it is likely that they will recommend a whole new control panel rather than any repairs. This is often quicker and cheaper.

#13: Kettling Noises

If your boiler is making noises like a kettle, the issue is likely to be related to sludge and other debris particlesin the central heating system.

This sludge is most commonly found in hard water areas where limescale build-up restricts the surface area of key components in your boiler such as the heat exchanger. This makes the limited water around those areas boil in exactly the same was as a kettle.

Once you get a limescale build-up, it can be very difficult to remove and the parts it tends to affect are often the more expensive ones to replace.

It is therefore highly advisable to fit a scale reducer to minimize the impact of scale on your system.

#14: Pilot Light Keeps Going Out

Our final problem is one of the most commonly found ones and relates to the pilot light going out. If this happens on a regular basis, the best advice is to contact an engineer straight away as this could be a serious issue with your gas supply.

This is not the only possible cause. The other common one is a build-up of carbon from the flame which can block the pipe that supplies the small amount of gas for the pilot light.

If it is windy outside, another possible cause is wind entering the flue and this draught causing the pilot light to go out. The thermocouple can also sometimes be faulty.

Because the problem can be related to gas, it is best to get a professional to check this out, but if the problem is caused by something else, it is usually pretty simple to fix.


If you are having problems with your boiler or central heating system, it is quite likely that we have detailed the cause and the fix in this guide.

The 14 different problems we have detailed cover all of the most common boiler fault issues and our explanation and fix recommendations should help you to resolve these issues fast if this is your problem.

If you have another problem that you would like some advice or have a comment on any of the problems we have detailed in this guide, please do share them with us in the comment box below.

We aim to respond to all queries and comments as quickly as possible.

Leave a Reply

Your email address will not be published. Required fields are marked *