Boiler Fault Guide
Boiler Not Firing Up? What to Check First
If your boiler is not firing up, first check whether both the heating and hot water have stopped. Then check its power, controls, pressure and fuel supply. A boiler doing nothing needs different checks from one that tries to light and locks out.
Insights by Vector Heat
When you call us, one of the most useful things you can tell us is what happens when you ask the boiler to run. Does the screen change? Can you hear a pump or fan? Does it try to light, then stop? You can gather that information without taking anything apart.
First Establish Whether Heating and Hot Water Work
It could be the middle of summer and nobody has tried the heating for months. Do not assume it works because it worked last winter. Provided there are no danger signs, make a short test using the normal controls.
- Photograph or write down the settings. You can put them back afterwards.
- Ask for heating. Select Heating On or a temporary override, set the thermostat above the current room temperature and make sure a radiator valve is open. Close the hot taps.
- Allow several minutes. Check whether the boiler fires and the radiators begin warming. A thermostat light or pump hum alone does not prove that the burner is running.
- On a combi, test a hot tap separately. Cancel the heating demand, then open a hot tap with a normal flow. Watch for a change on the display and whether the water heats.
- Restore your settings. Cancel temporary overrides once the test is finished.
A weather-compensated summer setting can prevent heating during warm weather. If you cannot establish that the controls are asking for heat, tell us the heating is untested, rather than declaring it faulty.
With a cylinder, hot taps do not prove that the boiler works. The water may already be hot, or an immersion may be heating it. Note whether the boiler responds to a normal hot-water reheat request when the cylinder needs heat.
If the heating works but the taps stay cold, use our boiler not heating water guide. That is a different starting point from a boiler that will not run at all.
What Happens When You Ask the Boiler to Run?
| What happens | Start here |
|---|---|
| Normally lit display is completely blank | Power supply and normal on/off controls |
| Display is on, but nothing changes | Heating mode, schedule and thermostat demand |
| Pump or fan starts, then clicking or a fault appears | Record the sequence and code; check fuel and permitted user checks |
| Burner lights, then immediately stops or overheats | Arrange diagnosis; ignition, flame detection and circulation need distinguishing |
| Combi fires for a tap but not heating | Heating controls and demand, rather than assuming the burner cannot light |
These are clues, not a parts list. A clicking boiler does not automatically need an ignition electrode, and a blank screen does not automatically mean a failed circuit board.
Four Simple Checks Before Booking a Repair
1. Check the Power
Gas, LPG and oil boilers all need electricity. Check whether the rest of the house has power, the boiler's normal switch is on and its usual display or light is present. An accidentally switched-off supply is worth ruling out.
If the circuit has tripped, note it. Do not keep resetting a breaker that trips again. Leave electrical covers closed, and do not replace fuses repeatedly or open the boiler to investigate. A burning smell or water near the electrics needs professional help.
2. Check the Thermostat, Timer and Heating Mode
Check the current time, today's schedule, holiday mode and whether heating has been turned off for summer. A power cut can change the clock or settings. The thermostat's target must be above the room temperature for a heating test.
Check user-replaceable thermostat batteries if the display is blank or shows a low-battery warning. On a wireless control, note any lost-connection message. A working phone app does not prove the boiler has received a heating demand.
If those settings are correct but the boiler never responds, the receiver, wiring or a motorised valve can be involved. Photograph the controls; leave their electrical covers and wiring alone.
3. Read the Pressure Gauge
On a sealed heating system, low pressure can stop the boiler operating. Check it when the system is cool against the range in your manual. Many systems are around 1-1.5 bar cold, but use your own system's instructions.
If the manual allows a homeowner top-up, there is no visible leak and you can identify the correct filling controls, follow that procedure slowly and close them fully afterwards. Do not guess which valves to open. An open-vented system with a header tank may have no pressure gauge or filling loop.
Has somebody recently bled the radiators? That can lower sealed-system pressure. If pressure repeatedly falls, or rises sharply when hot and drops to zero when cold, follow our boiler pressure-loss guide. Repeatedly adding fresh water introduces oxygen and can increase corrosion; topping up is not a repair.
4. Check the Fuel Supply
For a prepayment gas meter, check credit and whether the supplier's normal reconnection procedure is needed after topping up. Check for a reported supply interruption. If another gas appliance was already working normally, that is useful information, but it does not prove the gas pressure at the boiler is correct.
Do not light another appliance as a test if you smell gas. Never adjust a gas regulator, disturb meter fittings or reopen a supply that an engineer has isolated. Oil and LPG customers should also check their tank level, as explained below.
Boiler Not Working in Freezing Weather
A frozen condensate pipe can stop a condensing boiler. It carries waste water away and is normally plastic; part of it may run outside to a drain. Gurgling and a lockout during freezing weather can fit this pattern, but neither proves it by itself.
If you can positively identify the external condensate pipe, it is safely accessible at ground level and your manufacturer's instructions allow it:
- Apply warm, not boiling, water to the frozen section, or use a hot-water bottle against the pipe.
- Take care on icy ground. Spilt water can freeze and create another slip hazard.
- Once thawed, use the permitted reset procedure below. Stop if it still will not run.
Do not climb to reach it, use a flame or heat gun, disconnect pipework or open the boiler's condensate trap. If you are not sure which pipe it is, ask. Worcester Bosch's frozen-condensate guide shows the basic check. Repeated freezing needs a lasting pipework solution.
Read the Fault Code Before Resetting
A lockout means the boiler has stopped after detecting a problem. Photograph the full code and note the make and model. If it uses a flashing light, take a short video so we can see the pattern. A still photograph cannot show the timing.
Check the exact model's user instructions. Only reset where those instructions permit it and a simple cause has been resolved, such as restoring the normal supply or thawing a frozen condensate pipe. One controlled attempt is enough for these checks. If it fails or the same fault returns, stop and arrange a repair.
There is no universal button or hold time. Our Worcester reset guide shows how the controls vary. A modern condensing boiler does not have a standing pilot light to relight with a match.
Oil or LPG Boiler Not Firing Up
The power and control checks still apply, but you also have a stored fuel supply to consider.
- LPG: read the tank gauge or normal cylinder-supply indicator and contact your supplier if the supply has run out or appears interrupted. Leave regulators and supply faults to the supplier or a suitably qualified LPG engineer.
- Oil: check the tank gauge and note any recent run-out or delivery. Air can remain in the fuel line after a tank has run empty, so refilling does not always restore operation.
Do not keep pressing an oil burner's illuminated reset button. A lockout needs its cause established, and repeated resets can cause further problems. Do not bleed the oil line or dismantle the burner yourself. Arrange a qualified oil-heating engineer if the normal checks do not resolve it.
When You Need an Engineer
If the boiler has power, a genuine demand and fuel but still will not run, it needs fault finding. Depending on the sequence, we may need to check the controls, valves, circulation, fan, ignition or flame detection. The fault code helps direct those tests; it does not always name the failed part.
Internal gas and LPG work needs a Gas Safe registered engineer with the relevant fuel and appliance qualifications. Oil work needs a suitably qualified oil engineer. Leave the case, combustion chamber and flue alone.
Send Us These Details
- Boiler make, model and fuel: gas, LPG or oil.
- Whether heating, hot water or both have stopped, and what you actually tested.
- Whether it does nothing, starts a pump or fan, clicks, lights or locks out.
- A photo of the code and pressure gauge, or a video of a flashing light.
- When it started, any power cut, fuel run-out or recent work, and what happened after any reset.
Do not recreate a dangerous fault to record it. Tell us about the problem when booking: this is a repair or fault-investigation visit, not a routine boiler service. We need to allow time for diagnosis and, where necessary, obtaining parts.
Frequently Asked Questions
Why is my boiler not firing up when the thermostat is on?
Check that the target temperature is above the actual room temperature and the heating schedule is on. The thermostat also needs to communicate with the heating system. Its display can be working while the receiver, wiring or a motorised valve prevents the boiler receiving a demand.
Why is my boiler clicking but not igniting?
It may be attempting ignition without establishing a flame. Fuel supply, ignition components, flame detection and condensate problems are possible causes. Clicking alone does not identify the failed part. Record the code and stop if a permitted reset fails; do not open the casing.
Can low pressure stop a boiler firing up?
Yes, on a sealed system the boiler may stop below its permitted pressure. Use the cold-pressure range in your own manual, commonly around 1-1.5 bar. Pressure that keeps falling needs investigation. An open-vented system with a header tank is different and may not have a gauge or filling loop.
Why is my boiler not working after a power cut?
The boiler may still have no supply, or the programmer's clock and schedule may have changed. Check the normal power switch, controls and displayed fault. If it has locked out, follow the exact model's user instructions. Do not assume every boiler needs resetting after a power cut.
Why does hot water work but the heating will not come on?
If a combi actually fires for a hot tap, the burner can operate. Check heating mode, schedule and thermostat demand before assuming an ignition fault. With a cylinder, stored hot water or an immersion can supply the taps even when the boiler is not working.
Should I keep resetting a boiler that will not fire?
No. Make one controlled attempt only where the exact model's instructions allow it and a simple cause has been resolved. If the fault returns, stop and arrange a repair. Do not reset after a violent ignition bang, gas smell, overheating or another danger sign.
Does a boiler that will not ignite need replacing?
Not necessarily. A controls problem or repairable component fault can stop an otherwise sound boiler. Diagnose the cause first, then consider its condition, repair history, parts availability and repair cost. Not firing up is a symptom, not a reason on its own to replace the boiler.
Boiler Not Working in Lincoln or Lincolnshire?
Send Vector Heat the details above and we can arrange the right investigation. You do not need to decide which part has failed before contacting us.