14 Heating and Boiler Problems Explained (and Fixed)

Having heating or boiler problems?

1 in 5 boilers break each year. And, many of these boiler breakdowns could have been avoided by early troubleshooting, an annual boiler service, and putting some preventative measures in place.

Our 3-minute guide will cover 14 of the most common boiler problems, and what you need to do next.

These are problems that occur with all major brands including Ariston, Baxi, Glow-Worm, Halstead, Ideal, Vaillant and Worcester among others.

Safety Note Regarding Boiler Problems And Repairs

If you have heating or  boiler problems, you should get a quote from a boiler repair specialist that is Gas Safe engineer to start the troubleshooting process.

More than anything, working on a boiler without being Gas Safe registered is putting people in your property at danger.

And, to help you determine if replacing your boiler is the most cost effective option, you can get a fixed price online for a new boiler on Heatable’s website. They get incredible deals on Worcester boilers.

Worcester Bosch boilers - Trustpilot review

The Heating and Boiler Problems We Will Cover

If your heating and boiler problems are not covered in this article, please leave a comment and we will answer as soon as possible.

Problem 1: Boilers That Switch Themselves Off

One of the common boiler problems we face (almost weekly), is being called out to boilers that switch themselves off.

This either happens every few seconds, or every few minutes.


Because boilers are fitted with various fail-safes that kick in in certain scenarios. And, this is called a boiler lockout.

If your boiler seems to be “randomly” switch itself off, it’s likely due to one of the following reasons:

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

Prefer a replacement over a repair? Jump over to Heatable and get a fixed price on screen, in less than two minutes.

Problem 2: Boiler is Losing Pressure

Boiler problems link back to loss of pressure on many occasions. Here, you can see an in-depth guide to the causes behind boilers losing pressure.

We have several people ask is if a boiler can lose pressure with no leaks.

The answer is no. A leak, however small, causes pressure loss. You just might not be able to see where it is coming from.

If you’re pressure gauge constantly drops overnight, one of the reasons is likely to be:

  1. The pressure relief valve (PRV) is not working correctly.
  2. The auto air vent is broken and leaking pressure.
  3. There are leaks in your system. This could be on towel rails, radiators, rad valves or pipework.
  4. Your radiators are full of air.
  5. The expansion vessel is faulty.
  6. Old joints have degraded and are leaking.
  7. The pressure gauge on the boiler isn’t working correctly.

If you find the boiler pressure loss is only when the heating is on, that’s a sign of a small leak. The excess pressure caused by increased heat puts extra strain on the component leaking.

If your boiler loses pressure even when the heating and boiler is off, it’s a slightly larger leak.

Problem 3: The Boiler Constantly Leaks!

A lot of the time, boiler leaks are superficial. In most cases, they are unlikely to cause huge amounts of damage.

However, we have been called out to properties where small leaks have ended up corroding parts (leading to expensive repairs).

Even worse, if the water gets into the boiler PCB (£400-500 to fix) sometimes the best option is for a complete boiler replacement.

You can see an in-depth article on boiler leaks here. Most boiler problems that lead to leaks have been listed below:

  1. Expansion vessel diaphragm has degraded.
  2. Cracked heat exchanger.
  3. The heating pump is not secure.
  4. The heating pump has blown seals or gaskets.
  5. Boiler leaks when it rains, because water is entering via the flue.
  6. The filling loop is leaking.
  7. Pipework connected to the boiler is not soldered/installed correctly.
  8. The pressure release valve has failed.
  9. Internal parts have corroded and are now leaking.

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Problem 4: Noisy Boilers

As parts degrade, some boilers develop faults that result in banging, or gurgling noises.

Central heating pumps are one of the main reasons that these noises occur. Over time, they can build up with air which results in an airlock.

Luckily, this boiler fault is one that’s easily fixed. To remove an air lock from a central heating pump simply locate the pump behind the boiler casing.

There is a small bleed screw that is designed to let air out. Once the air stops hissing and trickle of water comes from the bleed screw the airlock should be removed.

Got a problem with boiler noise? We’ve created a guide to noisy boilers here.

Problem 5: My Boiler Makes a Loud Bang When It Fires up

Does your boiler make a loud bang when it starts up? Possibly like a small explosion? Well, there’s a good chance it is an explosion.

Listen just before your boiler starts up. When you turn the heating on, the boiler will try to ignite. If it doesn’t ignite after 3 attempts, it will probably lock out.

However, if it manages to fire on the 2nd or 3rd attempt, they’ll be excess gas in the chamber. The ignition is now lighting much more gas than it needs to.

The fix is usually a replacement ignition burner. This wear out and break over time.

Problem 6: Hot Water Doesn’t Work, But Heating Does (or vice versa)

This is a common boiler problem with older units. And there is usually one culprit; the diverter valve.

The diverter valve filters hot water to your taps/showers, as well as your heating. It will always focus the most water towards taps and showers. Once you turn these off, it then focuses all hot water to the heating.

The valve is known to get stuck over time, mainly due to debris and sludge build up. When this happens, it will either stick on the heating, or hot water side.

If it sticks on the heating side, you’ll only get Luke-warm water at best. And, if it sticks on the hot water side, you’ll only get Luke-warm heating at best.

We’ve covered some useful points that can help you troubleshoot a faulty diverter valve here.

Spares kits are available for diverter valves to fix this heating fault, but as the unit is already worn, it’s worth looking at a full replacement. You can get a price on-screen in less than 90-seconds here.

If you’re still struggling, check out our guide to no hot water.

Problem 7: No Heating or Hot Water

Most central heating systems will use a boiler that has a motorised control valve, sometimes called a mid-position or Y-plan valve. Valves are prone to failing and when they do, they get stuck. If you have no hot water or heating, then this could be the issue.

Get a heating engineer to check that the valves are operating correctly.

There’s a full guide on what to do when you have no hot water here.

Problem 8: The Boiler Works, But Radiators Won’t Heat Up

If the boiler is firing up, that’s a good sign. If radiators are not heating up at all, there’s a few common culprits.

The first part of the troubleshooting process will focus on the pump. Old pumps are prone to seizing. When this boiler problem occurs, hot water will not be directed to any radiators, taps or showers.

Giving the pump a gentle tap can sometimes free it up enough to get it working again. However, it’s likely that its coming to the end of its life and is probably going to need to be replaced soon.

Before you replace the heating pump. Try bleeding all radiators and towel rails. Large pockets of air in a heating system can stop it working altogether.

If they radiators are hot at the bottom and cold at the bottom, there’s a good chance heating sludge is the issue.

Problem 9: Water is Far Too Hot

If water is coming out far too hot, then this is likely to be a thermostat issue. The thermostat obviously thinks the water is much cooler than it is. If your central heating system uses a hot water tank or cylinder, the cylinder thermostat is likely to be the culprit.

A new thermostat will fix this heating problem.

However, if the water is coming out far too hot from your shower, the thermostat probably isn’t too blame.

The cartridges in showers are prone to failing. If they have failed whilst set on a hot setting, it’s likely that they are stuck there.

So, the shower cartridge will need to be replaced.

Problem 10: Boiler lockouts and Condensate Issues

Hopefully, you have your boiler manual to hand.

If you are finding that your boiler problem is lockouts, there should be a fault code on the PCB display.

Cross check the fault code with your user manual.

Many boiler lockouts are associated with condensate blockages.

All boilers now must be condensing. What this means is that they catch all the acidic water and waste gas that the boiler produces.

Once this is collected, its distributed to the outside draining system, so no harmful gases are in your property.

The problem is that the condensate pipe that takes the water and gases out of the property is incredibly small.

In the winter, this means it’s prone to freezing. All other times of the year its prone to developing small blockages.

A frozen pipe is extremely easy to unblock. Get some warm water and pour it over the pipe until it thaws out.

If it’s just a small blockage. Try removing the pipe, flushing hot water through out and then reinstalling it.

If this doesn’t work, all plumbing merchants stock condensate pipes. A replacement is going to be in order.

And, if you’re still having problems, checkout our guide to boiler lockouts here.

Problem 11: Radiators are Cold at The Bottom, Middle or Top

If your radiators are not heating up correctly, it’s important to check which part of the radiator isn’t working.

A common issue we come across is that new radiators have not been balanced correctly.

Balancing radiators ensures the right amount of hot water reaches each radiator to give an even distribution of heat.

Top of Radiators Won’t Heat Up

If radiators won’t heat up correctly, or the heat on the radiators is patchy, this usually signifies that there is air trapped in the system.

Using a radiator bleed key open the air vent (very slowly, and probably less than a quarter of a turn). When the air stops hissing out and water starts dripping the radiator is bled. Do this on every radiator and towel rail in the house.

Middle & Top of Radiators Won’t Heat Up

This boiler problem relates to a build-up of debris (mainly sludge) in your central heating system. This sludge build up will damage all parts in the heating system, including pumps, heat exchangers and even the radiators.

If you’re finding the radiator is cold but the pipes are hot, even after bleeding, sludge is likely the problem.

You have a few options:

  1. Hot flush (run chemicals through the system at normal flow rate and pressure).
  2. Power flush (a pressurised hot flush).
  3. Replace radiators that have sludge build up.

Once the radiators have been fixed, it’s important to install a boiler sludge filter.

Magnaclean and Fernox are two good brands of boiler sludge filters to consider.

Problem 12: Boiler Controls are Not Working Correctly

A common boiler problem we come across is controls not working correctly. This can make it look like there are other faults, but they are purely electrical.

This can be a thermostat, mechanical timer, or frost thermostat.

Your boiler controls are likely to be the issue if:

  1. Your boiler turns on and off when it’s not meant to.
  2. The temperature seems much hotter or colder that it shows on the thermostat.
  3. Thermostat is not clicking.
  4. Thermostat or mechanical timer is buzzing.
  5. Radiator valves are not increasing or decreasing temperature according to their setting.
  6. Water is coming out far too hot.

In many cases (if you don’t have a wireless or internet thermostat/programmer), it’s much cheaper to replace the boiler controls than repairing them.

Checkout this guide if your boiler timer isn’t working.

Problem 13: Kettling Noises

If your noisy boiler sounds like a kettle coming up to the boiler, your problem is likely to relate to sludge and particles in the central heating system. But what really is boiler kettling?

Sludge is a common build-up of debris in the system. In general, it’s particles from the water that cause kettling noises. Most common in places that have hard water. You can see the different hard water areas in the UK here.

This build up will then restrict the surface area in components such as the heat exchanger.

This means the limited water in there is literally boiling, acting in the exact same manner a kettle would. This is the noise that you can hear.

It can be extremely hard to remove scale from hard water once it builds up. And unfortunately, it attracts itself to expensive parts such as the heat exchanger. If the parts can be salvaged, make sure you fit a scale reducer to stop kettling from happening again.

Problem 14: Pilot Light Keeps Going Out

If your boiler problem is a pilot light that keeps going out. Phone a Gas Engineer straight away.

Because this relates to gas, it could be extremely dangerous.

The gas supply could be the issue. For example, if a gas valve has been turned off in a property because it was vacant, there would be no gas to the boiler.

What we find is that carbon builds up over time and this can block the pilot light.

If it’s extremely windy outside, wind could be entering the flue and this draught could be causing the pilot light to go out.

Finally, the thermocouple might be faulty.


Want a quote for a new boiler? You can get one on-screen in less than two minutes on Heatable’s installation quote form.

Heating and boiler problems come in all shapes and sizes. Many faults can be rectified without replacing the boiler, so it’s important to go through a proper troubleshooting process.

And, if your heating problem has not been listed, please leave a message in the comments and we will get back to you.



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  1. A bathroom radiator is hot at bottom and warm to cold at top. Rad is old. Bleed valve is a square set inside a square
    hole inside a six sided nut 3/4 inch across flats. I don’t have a tool which fits the valve. If I loosen outer nut with a wrench will that release air in same way as via the valve? Thanks/regards.

  2. Our new bungalow has a central heating and hot water system that when filled and working loses pressure at about 0.5bar per day. When shut down and wet pressure tested it also loses pressure and leak cannot be found but when drained and air tested the pressure does not drop – any ideas? please. There are no damp patches anywhere.

  3. I have a Potterton Profile 80e boiler installed c.2000. It works perfectly well i.e. fires smoothly and generally has performed excellently over the years, with regular service. But recently I have noticed a clanging or expansion noise which comes up twice or thrice over a period of a few minutes of starting from cold only after it has been off for some hours and this disappears completely after that and the boiler then works perfectly. The system is a gravity CH system with a Grundfos CH pump. I am a layman and have have no knowledge of CH systems. Bleeding of the pump by a gas safe engineer whom I got to look at it indicated no air and he was not able to put a finger on what the cause was except to say ‘do not worry about it and there is no danger’. While he was here the noise appeared just once or twice after which there was none until the boiler was left unused for several hours. Radiators are bled whenever required. I wonder whether anybody has experienced this and if so how it was overcome. I would be happy to get a gas safe engineer look but would like a resolution rather than paying out to end up with no proper diagnosis and remedy. Thanks.

  4. My Baxi80, installed 2004, locks out after a length of time,a number of hours, normal operation. The next morning it comes on using MAN on the remote thermostatic control and repeats this process every day- without fail over a week now.
    Gas and water pressure are ok. What possible causes are there for this?

  5. I have a Worcester bosh combi boiler that for some reason when the heating is on it will stop heating when you run a tap weather its the hot or cold

  6. My Worcester boiler has a wireless Salus thermostat and receiver. The receiver has started staying on when the thermostat is not calling for heat. We’ve changed the batteries in the thermostat, reset the boiler, but it’s still doing it. Can you advise please?

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