Why does my boiler keep turning off?

A boiler that fires, runs for a minute or two and then shuts down is not being temperamental. It is protecting itself, and it will keep doing it until the underlying fault is dealt with.

The pattern of the shutdown tells you a lot, so pay attention to how long it runs before it stops.

Low system pressure

Check the pressure gauge first. A sealed system should sit at roughly 1 to 1.5 bar when the heating is cold, rising to around 2 bar once it is hot.

Below about 0.5 bar most boilers lock out rather than run dry. Topping it back up through the filling loop is a five minute job, but the real question is why it dropped. A sealed system should hold pressure for months. If you are topping it up every few weeks you have a leak, and our page on boiler pressure that keeps dropping works through where it usually is.

Overheating and short cycling

If the boiler fires hard, gets hot fast and cuts out within a couple of minutes, it is hitting its overheat thermostat.

That means heat is being generated faster than the system can carry it away. The usual causes are a seized pump, a closed valve, a blocked heat exchanger, or a system so full of sludge that the water cannot circulate. Sludge is the most common of the four in older Manchester housing stock, and it is what a power flush is for.

Short cycling wears out a boiler quickly. Every ignition cycle is a small amount of wear, and a boiler doing that six times an hour is aging fast.

A frozen condensate pipe

If this started on the first properly cold morning of the year, this is almost certainly it.

Every condensing boiler produces mildly acidic condensate that drains away through a plastic pipe, usually 21.5mm or 32mm. Where that pipe runs outside and the temperature drops below freezing, it blocks with ice, the condensate backs up, and the boiler shuts down to avoid flooding itself. Most boilers show a specific fault code for it.

You can often thaw it yourself with warm, not boiling, water poured along the outside pipe, then reset the boiler. If it happens every winter the pipe needs re-routing internally or lagging properly, which is a permanent fix rather than an annual ritual.

Ignition and flame failure

If the boiler tries to light several times, clicks, then locks out with a fault code, it is failing to establish or detect a flame.

Common causes are a dirty flame sensing electrode, a failing ignition lead, a gas supply problem, or a blocked flue or condensate trap. This is Gas Safe territory. Do not keep hitting reset. Repeatedly resetting a boiler that is failing to ignite is one of the few genuinely unwise things you can do with one.

Controls that look like a fault

Before assuming the worst, rule out the boring explanations. A room thermostat set close to the current room temperature will satisfy quickly and shut the boiler down, which looks like short cycling. So will a system where nearly every thermostatic radiator valve is closed, leaving the boiler nowhere to send its heat.

What to note before ringing

• The exact fault code on the display

• The pressure on the gauge when the system is cold

• How long it runs before it stops

• Whether it does it on heating, hot water, or both

Those four answers turn a diagnostic visit into a repair visit.

Getting it fixed

Most of these are repairs rather than replacements. We find the fault, tell you what it is, and price the work before starting.

See our boiler repair page for how we handle it, and note that an annual boiler service catches the sensor, seal and condensate problems that cause most winter lockouts. We cover Manchester, Salford and the surrounding towns.

If you smell gas at any point, ring the National Gas Emergency Service on 0800 111 999 before you ring us.

Otherwise, 0161 515 9977.