Boiler Lockout: Causes and What To Do

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Last updated: October 31, 2023
boiler lockout

Are you experiencing a boiler lockout but are not sure what it means, what’s causing it or how to fix it? Not to worry; in this guide, we cover absolutely everything you need to know about the boiler lockout, including the main faults that cause this problem and the steps you can take to solve it.

What Is A Boiler Lockout?

A boiler lockout is a shut-down procedure initiated by your boiler when it detects an issue with one of its components or alternatively with the entire system. It’s a safety feature that helps prevent problems from becoming dangerous to your boiler, home and yourself as it rules out the risks of explosion, fire and damages to the components.

While not having heating or hot water can be frustrating (especially in the colder months when you need them the most!) an automatic boiler shutdown is a beneficial feature as it prevents the boiler from firing up when there’s an issue within the system. In essence, a boiler lockout helps keep your boiler safe even when something is not working correctly.

But how do you identify a boiler lockout? The first and most obvious sign is, of course, not having hot water or central heating. But aside from this, your boiler will let you know it’s experiencing problems in other ways as well. An older boiler model will flash a red or green light on its display panel, while a newer one will usually display a fault code, which looks like a string of letter and numbers.

What To Do When Your Boiler Locks Out

Whether your boiler is flashing lights or displaying a fault code or both, the first step to solving the issue is figuring out what the problem is about. Here’s how you can do this:

Check your boiler manual: to begin with, refer to your boiler manual is it contains all possible fault codes as well as their explanations.

Visit the manufacturer’s website: if your manual doesn’t contain the error code your boiler is displaying, check the boiler manufacturers website as they should have a list of all error codes and their causes.

Call the manufacturer’s customer support line: if you have an older boiler that doesn’t display fault codes at all, call your boiler manufacturer’s customer support line and ask them what to do next. They will likely tell you to hire a heating engineer, however, there is always a chance that they might know what the problem is.

Fix the problem: one you know exactly what’s causing the lockout issue, figuring out the best way to fix the problem will be much easier. Sometimes, a simple boiler reset can do the trick, however, if you’re frequently having to deal with a boiler lockout, it’s much better to fix the underlying problem and find a long-term solution than to slap on a band-aid on it and move on. Read on for common boiler lockout causes and the best ways to fix them.

Boiler Lockout Causes

A boiler lockout is pretty common in older boilers, however, newer models are not immune to automatic shutdowns either. A boiler can lockout due to a wide range of factors, including something simple as a glitch or power cut, as well as something more serious like low pressure or a major safety issue.

While every boiler is different and the lockout can be caused by a variety of things, there are some common problems that we see occurring with practically every boiler that can lead to a boiler lockout.

Faulty Pump

It’s pretty common for central heating pumps to develop faults, blow seals or seize up. If you can feel small vibrations coming from the pump, you’re in the clear as this means that the pump is working. However, if it feels very hot to touch, its internal parts might be jammed. Often, a simple tap can free seized up parts so give it a little tap; just make sure you’re gentle!

Low or High Pressure

Most boilers operate at a pressure between 1 and 1.5 bar, although some models go up to 2.5 bar with no issues. Of course, to find out what your boiler’s optimum pressure is you should refer to your boiler manual. Generally though, most boilers will lockout if the pressure is below 0.6 bar or above 3 bar. If your boiler pressure is low, you can increase it by adding water to the system via the filling loop. If the pressure is high, you can reduce it by bleeding the radiator valves.

System Blockage

It’s not uncommon for boilers, pipework and radiators to become blocked with sludge. Equally, the condensation pipe that vents outside can freeze, especially in the winter and generally cold mornings. Both of these issues can lead to a boiler lockout. If you’ve never flushed or cleared your central heating system, we recommend hiring a heating engineer or an experienced plumber to do it for you because if you don’t manage to clear the sludge blockage correctly, you can cause even more damage to the system.

Heat Exchanger Blockage

The heat exchanger can also become blocked with limescale. If you can hear a sort of whistling or kettling noise coming from your boiler, it’s likely that there’s limescale buildup, which can result in water temperature rising too high and triggering a lockout. Unfortunately, repairing a damaged heat exchanger is often not cost-effective if you have an old boiler as the repair costs are quite high. The good news is that you can help prevent this problem in the future by getting a limescale reducer.

Fan Issues

The fan is an essential component of every boiler as it pushes toxic gases through the flue and out of your home. If the fan is faulty, your boiler could become dangerous so the boiler circuit won’t allow it to turn on. If the problem is with the fan, a Gas Safe registered engineer will have to replace it.

Ignition Problem

Most boilers are programmed to lockout after three failed ignition attempts. To see if this is the issue, check the ignition leads and probe. If you’re indeed having this problem, the boiler will likely have to be stripped down so that the ignition and flame sensor probes can be cleaned.

No Power

Finally, a boiler lockout can be caused by a power failure. The problem could be due to a recent power cut, tripped electrics or a blown fuse. Rarely, the issue can be caused by the printed circuit board (PCB), which is the most serious issue of all.

How Do I Reset My Boiler?

Once the fault has been identified and fixed, it’s time to reset your boiler. Most modern units have a reset button right on the boiler display board. Press the reset button and hold it down for a few seconds in order to reset the boiler. Usually, 5 to 10 seconds will do it, however, it’s best to consult with your manual to see what the exact reset procedure is for your make and model. If you want a more detailed guide, you can check out our How to Reset a Boiler article.

If you have an older model that doesn’t have a reset button on their front, again, it’s best to refer to your manual to find out what process is required. If you don’t have the manual, you can visit the manufacturer’s website to find out where the reset button is on your boiler; alternatively, you can call their customer support line to ask for help.

Bear in mind that resetting your boiler after it has gone into lockout mode won’t resolve the problem. For this reason, we strongly advise you to first identify the issue and resolve it before trying to reset the boiler.

How to Solve Regular Lockouts

If you’re experiencing frequent boiler lockouts – i.e. as soon as you identify one fault code and fix it, your boiler is finding out another fault code – it’s more than likely that your boiler is on its last legs. If this is a very common issue you have to deal with, the best option is to stop paying for frequent repairs and component replacements and invest that money in a new boiler.

Now, we know you didn’t click on this article just so we can tell you to purchase a new boiler, however, sometimes it is more cost-effective to invest in a new unit than to constantly pay for repairs for the old one. Aside from saving your hard-earned money on repair bills, you will probably also save on energy bills too because modern boilers are incomparably more energy-efficient than their older counterparts (this is especially true if your boiler is older than 10-15 years). And if you get a long boiler warranty (which we always recommend!), your new boiler will be covered for any faults that may occur in the next few years. If you do decide to buy a new unit, remember to get multiple quotes so you can get the best possible deal!


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