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Boiler Faults and Fault Codes

Common Boiler Faults in Birmingham

What is wrong with your boiler, in plain English. Find your symptom or fault code below for the likely causes, the safe checks you can make yourself, and when to stop and get a Gas Safe registered engineer.

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What is your boiler doing?

Pick the symptom that matches. Each guide starts with the short answer.

What does your boiler's fault code mean?

Fault code meanings below are checked against each manufacturer's own manuals and fault tables. Codes can differ between models, so always check the manual for your boiler too.

BrandCodeGuide
VaillantF22Vaillant F22 fault code
VaillantF28Vaillant F28 fault code
VaillantF75Vaillant F75 fault code
Worcester BoschEAWorcester Bosch EA fault code
Worcester BoschE9Worcester Bosch E9 fault code
BaxiE133Baxi E133 fault code
IdealF1Ideal F1 fault code
IdealL2Ideal L2 fault code
Glow-wormF1Glow-worm F1 fault code
Glow-wormF2Glow-worm F2 fault code

Which make is your boiler?

Each brand guide covers that make's common faults, a fault code table checked against the manufacturer's own documents, and servicing advice.

The six faults we see most, at a glance

Boiler not producing heat or hot water

Symptoms

Taps run cold, radiators stay cool, no heating even with the thermostat turned up.

Likely causes

A failed diverter valve is the most common culprit in combi boilers: it sticks in one position and sends heat to the taps or the radiators but not both. Other causes include a faulty pump, a broken motorised valve, or a thermostat or timer that is not calling for heat.

The fix

Diverter valve and pump replacements are common combi repairs. Thermostat and timer issues can sometimes be solved by resetting the controls.

Read the full guide: boiler not producing heat or hot water

Boiler losing pressure

Symptoms

The pressure gauge reads below 1 bar. The boiler cuts out. You have to top up the pressure regularly.

Likely causes

In most cases a small leak somewhere in the sealed system is draining pressure slowly: a radiator valve, a fitting, or the boiler's pressure relief valve. If the relief valve's outside pipe is dripping, the valve may have failed or the expansion vessel may need attention.

The fix

Pressure that needs topping up more than occasionally points to a leak or a failing component that should be found and fixed by an engineer.

Read the full guide: boiler losing pressure

Boiler making strange noises

Symptoms

Banging, clanking, whistling, gurgling or a kettle-like rumbling from the boiler or pipes.

Likely causes

Kettling, the rumbling sound, is caused by restricted flow through the heat exchanger. Birmingham has soft water from the Elan Valley, so limescale is less of a culprit here than in hard-water cities, and sludge from system corrosion is the more common cause locally. Gurgling usually means air or a partly blocked condensate pipe.

The fix

Depending on the cause, bleeding radiators, a system clean to remove sludge, or a pump repair. A magnetic filter helps protect the system afterwards.

Read the full guide: boiler making strange noises

Pilot light keeps going out

Symptoms

On an older boiler, the pilot light will not stay lit, or the burner lights briefly then cuts out.

Likely causes

On boilers with a standing pilot, a faulty thermocouple is the most common reason. Draughts, a dirty pilot jet or a gas supply problem are other causes. Modern boilers have no pilot light and use electronic ignition instead.

The fix

Thermocouple replacement is usually an inexpensive repair. Any work on the pilot assembly is gas work for a Gas Safe registered engineer.

Read the full guide: pilot light keeps going out

Frozen condensate pipe

Symptoms

Happens in freezing weather. The boiler locks out and shows a fault code, and you may hear gurgling from the boiler.

Likely causes

Condensing boilers drain acidic condensate through a plastic pipe that often runs outside. In a hard frost that pipe can ice up, and the boiler shuts down to protect itself.

The fix

You can often thaw the outside section yourself with warm, never boiling, water and then reset the boiler once. If it still will not run, send an enquiry.

Read the full guide: frozen condensate pipe

Radiators not heating evenly

Symptoms

Some radiators are hot and others cold, or one radiator is cold at the top or bottom.

Likely causes

Cold at the top usually means trapped air. Cold at the bottom is often sludge settling at the lowest point. Uneven heat across several radiators may be a pump or balancing issue.

The fix

Bleeding radiators is a simple DIY job. Sludge needs a system clean, and balancing means adjusting the lockshield valves.

Read the full guide: radiators not heating evenly

When should you stop and get a Gas Safe engineer?

Straight away if you smell gas, a carbon monoxide alarm sounds, water is leaking from inside the boiler, or a fault comes back after one reset. Never take the boiler casing off or work on gas parts yourself. For a gas smell, leave the property and call 0800 111 999.

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