Two other heating pieces already exist here. Low pressure is a gauge and a filling loop. Turning the heating on is a seasonal first fire. This page is the third problem: the boiler does not ignite, or it tries and locks out. Do not treat it as a replacement quote until a registered person has said the heat exchanger is finished. For pounds, use boiler replacement costs later.
If you smell gas, this page is over
Get out. Call 0800 111 999. Do not use electrical switches as you leave. Do not keep pressing reset to “see if it clears”. The Gas Safe notes exist for planned work. A smell of gas is the emergency line, not a directory.
A carbon monoxide alarm is the same stop. Out, fresh air, emergency number. Do not open the case.
Check the things that are not the burner
- Power at the fused spur and the boiler display. A blank display with a dead socket is not a new boiler.
- The programmer. Holiday, off, or a clock that still thinks it is July will look like a dead machine.
- The room thermostat and any thermostatic radiator valves. If every TRV is shut and the thermostat is low, the boiler has nothing to do.
- The gas cupboard tap, if you know which one it is and it is only a tap, not a joint you would have to undo. If you are not sure, leave it.
- Pressure, if there is a gauge. If it is on the floor, read the low-pressure piece before you invent a lockout.
Write down what the display shows. A letter-and-number fault code is what you read to an engineer. Photograph the model badge on the case. Do not take the cover off to get a better picture.
Reset is a single test, not a hobby
Many combis have a reset button the handbook tells you that you may press once. Press it once. Wait. If the burner lights and stays lit, watch it for twenty minutes and note whether it drops out again. If it does not light, stop. Repeated resets on a blocked flue or a failed flame sensor is how a small fault becomes a dangerous one.
Frozen condensate pipes in cold weather are a common lockout on condensing boilers. The handbook may describe a safe way to thaw the plastic pipe outside with warm water — not boiling water, not a blowtorch. If you cannot see the pipe, or it is on a roof, leave it.
Tenants should also check whether the landlord’s gas safety record is in date before anyone other than the landlord’s engineer opens the case. A cold house is still a repair, but the paper trail is theirs. Homeowners who have just moved in should find the last service note; a boiler that has not been serviced for years is a diagnosis visit, not a reason to keep tapping reset through an evening.
When to put the handbook down
- Any gas smell, unexplained hiss, or CO alarm.
- Water under the boiler or from a discharge pipe that will not stop.
- You have reset once and it locked out again.
- The case would have to come off for the next step.
- You are a tenant and the landlord’s gas certificate is out of date — that is their engineer, not a DIY cover-off.
Ask for a Gas Safe licence number on the call. This site does not email the engineer. Open plumbing and heating — London or Manchester — and use the number on the card. Say whether you want a repair diagnosis or a replacement priced as a second figure. Have the fault code and the model badge ready before you dial.
Questions before you keep pressing reset
Should I keep pressing reset?
Once, if the handbook allows it. If the boiler locks out again, stop and call. Repeated resets are not a repair.
Is this the same as low pressure?
No. Low pressure is a gauge and, sometimes, a filling loop. This page is ignition and lockout. Read both if you are not sure which you have.
Can I take the case off?
No. A sealed gas appliance is not a DIY panel. Call a Gas Safe engineer.
Where do I find an engineer?
Open a plumbing city list and use the phone number on the profile. Ask for the licence number. If you smell gas, call 0800 111 999 instead.
Need a heating engineer’s number?
Open plumbing and heating and contact the business yourself. If you smell gas, call 0800 111 999 instead.