Boiler Will Not Fire Up in Cold Weather? Four Usual Causes

You turn the heating on for the first time in months, the boiler tries, and nothing happens. Maybe it clicks a few times. Maybe a fault code appears. This is the single most common call we get on the first cold morning of the year in the North East, and there are four usual causes.

1. The condensate pipe has frozen

Start here, because in a frost it is the most likely answer by a distance. Condensing boilers drain acidic waste water through a plastic pipe. Where any of that pipe runs outside, a hard overnight frost can freeze it solid. The boiler detects the blockage and shuts down deliberately to protect itself.

Tell tale signs are a gurgling or bubbling noise before it stopped, and a fault code relating to condensate or a blocked drain. It is one of the very few boiler faults you can safely sort yourself with warm water and patience. Our guide to thawing a frozen condensate pipe explains how, and how to stop it happening again.

2. Ignition failure

The boiler is trying to light and cannot. You will often hear it attempt three times and then lock out. The cause is usually dirty or worn ignition electrodes, a failing gas valve, or a flame sensor that is not detecting the flame even though it is there.

These parts spend the summer doing nothing and then get asked to work. It is not a fault you can fix yourself, but it is a straightforward one for an engineer. The common codes are Baxi E133, Vaillant F28 and Worcester Bosch EA, and all three mean roughly the same thing.

3. Low pressure lockout

Look at the gauge. Most combis want 1 to 1.5 bar when the system is cold. Sitting in the red at the bottom and the boiler will refuse to fire at all. Topping it up is a two minute job with the filling loop.

The important part is what happens next. If it drops again within days, you have a leak or a failing expansion vessel, and topping up repeatedly makes things worse by introducing fresh oxygenated water that accelerates corrosion inside the radiators. See boiler pressure that keeps dropping.

4. The pump has seized

Six months of standing still is hard on a circulation pump. It works perfectly in April, sits motionless all summer, and will not turn in October. Sometimes the boiler fires but no heat reaches the radiators, sometimes it locks out on overheat because water is not circulating.

If the boiler fires and then cuts out quickly, or the pipes near the boiler get hot but nothing else does, a seized or failing pump is a strong candidate.

Before you call anyone

• Check the thermostat batteries. Flat batteries mean the boiler is never asked to fire.
• Check the timer, especially after the clocks change.
• Check a gas hob lights, to rule out a supply problem.
• Try one reset. How to reset your boiler covers it. If it locks out again, stop resetting and call someone.

Repeatedly resetting a boiler that keeps locking out will not fix anything and can make a small fault into a bigger one.

If you smell gas

Stop. Do not touch switches. Open windows, turn the gas off at the meter if you can reach it safely, get out, and ring the National Gas Emergency Service on 0800 111 999.

What if it is beyond saving?

Sometimes the honest answer is that the boiler has had its day, particularly if this is the second or third lockout in a winter. Our repair or replace guide sets out where the sums stop working, and if you are weighing up a replacement, Worcester Bosch versus Vaillant compares the two brands we fit most. It is also worth checking whether you qualify for help with the cost, which our guide to boiler grants in the North East covers.

We cover Sunderland, Newcastle, Durham, Washington, Houghton le Spring and the wider Tyne and Wear area, and we carry common parts so most of these are fixed on the first visit.