Typical reasons for a gas boiler to breakdown

When our boiler runs smoothly, it’s fair to say that we take it for granted; we expect it to give us heating and hot water whenever we need it, and don’t really give it much thought on a day-to-day basis. But when something goes wrong, it throws our home into chaos and we wonder how we’ll manage to get by until the problem is sorted.

Most boiler breakdowns happen in the cold winter months, because they haven’t been active for a while. When it’s brought back to life after a period of inactivity, your central heating system can feel the strain as it tries to heat your home; which can leave you with an expensive inconvenience you could really do without. Here are a few other causes for boiler breakdowns. Remember, don’t try and fix gas boilers yourself, always make sure you contact a Gas Safe registered engineer to come and help you out.

If it’s an old boiler

Old age is often an issue when it comes to boiler breakdowns. Corrosion and rust develop over the years, and can corrode connections, pipes and components. The result? Leaks and mechanical failure, leaving you without heat and hot water. As time goes by, debris can also accumulate and prevent the boiler’s mechanics from functioning properly, or restrict water from flowing through them.

If there’s no heat or hot water

There are lots of reasons why this could be. Perhaps it’s caused by a broken diaphragm and airlocks, or maybe the motorised valves have failed. Boiler pressure, the thermostat, or low water levels could also be causing the problem. Your engineer may be able to replace broken parts where necessary, depending on the scale of the issue however, if things have gone too far then it may be time for a new boiler.

If it’s leaking or dripping

The cause of this will depend where the water is coming from, and the engineer will be able to establish this for you. The most common explanation is likely to be a broken internal component, like a pump seal or pressure valve.

If it’s leaking from the pressure valve your boiler pressure could well be too high, if it’s coming out of the pump seal perhaps it’s worn out and in need of replacement. Sometimes, boilers can also leak around the pipes or tank and this can result from corrosion or an incorrectly fitted tank.

If the pilot light goes out

It could be that the gas supply is being prevented by a broken thermocouple (that’s a device within the boiler that measures temperature). Alternatively, a deposit could have built up in the pilot light.


If this happens to you, it’s always worth ensuring there are no issues with your gas supply. For example, if your gas stopcock is on but your boiler isn’t getting any gas or if none of your other gas appliances are working, then it’s time to call a gas supplier. British Gas offer both heating and boiler repair to all, not just those who are customers. If they say it’s safe to do so, then you can try reigniting the pilot light yourself – just remember to follow the instructions in your boiler manual.

If the condensate pipes are frozen

If you have a condensing boiler, it’s possible for the condensate pipes (which remove waste steam and condensation from your boiler) to freeze shut and stop it from working. Usually, the pipes run outside into a drain, which leaves them at risk of freezing when the temperature drops.

It’s easy to identify the condensate pipe on your boiler. Underneath, you’ll see pipes entering and exiting your boiler, and if you can see a plastic pipe (it’s usually white and roughly 2cm in width) then this is probably it. It’s likely to lead outside of your home and into a drain. Sometimes it’s possible to thaw a frozen condensate pipe by pouring hot water over it.

Do you have an annual gas boiler service?

Boilers can be complicated, so annual servicing is highly recommended. Professional Gas Safe registered specialists will take a look at every component to check they’re all in good and efficient working order, and this reduces the likelihood of a breakdown and increases a boiler’s life expectancy.