A fault code identifies which safety or operational check failed, which narrows the cause to a handful of possibilities but rarely names the faulty part. Replacing components on the basis of a code alone is how people pay for two repairs to fix one fault.
Check these before calling anyone
- Boiler pressure. The gauge should sit in the normal band – typically around one to one and a half bar cold. Below that, most boilers will not fire at all. If it needs topping up regularly, that is a leak and it is the real fault.
- The fault code on the display. Write it down exactly. It is the single most useful piece of information you can give us.
- The programmer and thermostat. Flat batteries in a wireless thermostat present exactly like a dead boiler. Check the display, and check the schedule has not reset after a power cut.
- Other gas appliances. If the hob does not work either, it is a supply problem rather than a boiler one – check the meter, including any prepayment credit.
- The condensate pipe in cold weather. A frozen external condensate pipe shuts a condensing boiler down. It is extremely common in a cold snap and often fixable in ten minutes – see frozen condensate pipes.
- The electrical supply. Fused spur, RCD, and any isolator switch near the boiler.
Call the National Gas Emergency Service on 0800 111 999. Turn the gas off at the meter, open doors and windows, do not operate any electrical switch, and do not use a naked flame. Get everyone out if the smell is strong. We deal with the repair afterwards – they deal with the emergency.
What fault codes actually tell you
A boiler has a set of sensors and safety devices, and its control board monitors all of them. A fault code says which check did not pass. That is genuinely useful, and it is not the same as naming the faulty part.
| Code family | What the boiler noticed | Common actual causes |
|---|---|---|
| Ignition lockout | It tried to light and did not prove a flame | Gas supply, ignition electrode, flame sensing electrode, gas valve, or a blocked condensate trap |
| Overheat | A temperature rose beyond the safe limit | Poor circulation – pump, airlock, sludge, closed valve – far more often than a faulty thermistor |
| Low water pressure | System pressure below the minimum | A leak somewhere, or a failed expansion vessel in the boiler |
| Fan or air pressure fault | The fan is not running, or the flue is obstructed | Fan, pressure switch, blocked flue, or a blocked condensate trap backing up |
| Flow or return sensor fault | A temperature sensor is reading implausibly | Sensor, wiring, or genuinely no flow |
| Condensate fault | Condensate cannot drain | Frozen or blocked condensate pipe – seasonal and very common |
| Flame loss during operation | It lit, then lost the flame | Gas pressure, flame sensing, or a condensate blockage |
Notice how often a blocked or frozen condensate trap appears in that table. It causes several completely different-looking codes, which is exactly why a code is a starting point rather than an answer.
The faults we find most
Circulation problems presenting as boiler faults
Overheat lockouts, kettling and short-cycling are very often nothing to do with the boiler. If water is not moving through the heat exchanger quickly enough, the boiler overheats locally regardless of how healthy it is. The causes are a failing pump, air, sludge, a closed or seized valve, or an oversized boiler on an undersized system. Replacing the boiler does not fix any of those.
Diverter valves
On a combi, an internal diverter directs heat to either the radiators or the hot water. When it sticks, one works and the other does not – the classic ‘heating fine, no hot water’ pattern. A routine repair on most appliances.
Scaled plate heat exchangers
The defining combi fault in a hard water area. The plate exchanger that heats your hot water on demand scales up, so hot water temperature and flow both fall. It is why water treatment matters here more than elsewhere – see scale inhibitors.
Expansion vessels
Inside the boiler, an expansion vessel absorbs the expansion of water as it heats. When it loses its air charge, system pressure swings wildly – low when cold, high when hot, sometimes lifting the pressure relief valve. It presents as ‘pressure keeps dropping’ and gets misdiagnosed as a leak.
Printed circuit boards
Sometimes genuinely the fault. Also the thing most commonly replaced when the real cause was never found, because it is the component you reach for when nothing else explains it. We would rather prove it than assume it.
Repair or replace
There comes a point where continuing to repair an old boiler stops making sense, and we would rather say so than keep coming back.
- Parts availability. Some appliances are genuinely unsupportable now, and a boiler you cannot get parts for is a boiler waiting to fail permanently.
- The heat exchanger. On most appliances this is the single most expensive part, and on an older boiler it can approach the cost of a replacement.
- Repeat failures. Three call-outs in two winters means you are renting reliability rather than owning it.
- Efficiency. An old non-condensing appliance running at a much lower efficiency costs meaningfully more every year it stays.
- What else needs doing anyway. If the system needs cleaning, the controls are inadequate and the radiators are wrong, a replacement is the moment those get sorted.
Equally, a well-made boiler that has been serviced properly and needs one component is worth repairing, and we will say that too. The decision is yours and you should have honest figures on both sides of it.
Boiler showing a fault code? Write it down before you reset it – it is the most useful thing you can tell us.
Questions we get asked about this
My boiler keeps losing pressure. What is wrong?
Either a leak somewhere in the system, or a failed expansion vessel inside the boiler. Check the pressure relief discharge pipe outside first – if it is dripping, the vessel is the likely cause. If it is dry, you have a leak to find.
Should I keep resetting the boiler?
Once or twice. If it locks out repeatedly, something is genuinely wrong and repeated resets achieve nothing useful. Note the code and call.
Heating works but there is no hot water.
On a combi, usually the diverter valve or a scaled plate heat exchanger. On a cylinder system, usually a motorised valve or the cylinder thermostat. Either way it is a component, not the boiler.
Is a boiler making a kettling noise dangerous?
Not immediately dangerous, but it should not be ignored. Kettling is localised boiling in the heat exchanger, caused by scale or poor circulation, and it shortens the appliance’s life. It is telling you about a system problem.
Do you carry parts?
We carry the common consumables and parts for the makes we see most. Where a specific part has to be ordered we will tell you on the day, including how long it is likely to take.
How do I know if I should replace rather than repair?
Ask what the repair costs, what else the appliance is likely to need, whether parts are still available, and what it is costing you in efficiency. We will give you those honestly, including when the answer is that your boiler has years left in it.
What happens when you call
Call and describe it
You speak to an engineer, not a call centre. Most jobs can be narrowed down on the phone.
We look at it properly
A real diagnosis before a price, and a straight answer if it is not worth doing.
A written quote
Itemised, so you can see what you are paying for.
The job, and the paperwork
Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
- Norwich
- Wymondham
- Dereham
- Attleborough
- Aylsham
- North Walsham
- Cromer
- Diss
- Loddon
- Long Stratton
- Watton
- King's Lynn
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.