Boiler Not Firing Up in Corsham - Common Causes and What to Do

Published July 2026 | Boiler Repair

In the first 10 minutes

When a boiler refuses to fire, the first ten minutes are about ruling out the obvious before assuming the worst. At least a third of the boiler call-outs our engineers attend in Corsham turn out to have a cause the homeowner could have fixed without a visit. Work through these checks before picking up the phone.

1. Check the thermostat. Make sure the room thermostat is set to a temperature higher than the current room temperature, and that any programmer or timer is in a "heating on" period. A timer knocked off schedule after a power cut will stop a boiler firing completely.
2. Check the pressure gauge. Most modern combi boilers need a pressure reading between 1 and 1.5 bar to operate. If the needle sits below 0.5 bar, the boiler will lock out as a safety precaution. The gauge is on the front panel - if it is low, this is likely your culprit.
3. Look for a fault code. If your boiler has a digital display, note down any error code showing. Worcester Bosch, Vaillant, and Ideal all use different code systems, but every code narrows the diagnosis considerably. Take a photo of it.
4. Test your gas supply. Try a gas hob if you have one. If the hob ignites normally, your supply is fine. If not, call National Grid Gas Emergencies on 0800 111 999.
5. Try a reset. Most boilers have a reset button marked with an arrow or flame symbol. Press and hold for a few seconds. If it fires briefly then locks out again, stop resetting - you have a fault that needs professional diagnosis.

Safety first: if you smell gas at any point, do not touch any switches. Leave the property, leave the door open, and call 0800 111 999 immediately.

Within the first hour

If the basics have not resolved it, spend the next hour narrowing down the likely cause before booking an engineer. This saves time and can often reduce the cost of the visit.

Repressurise the system if pressure is low. Most modern combi boilers have a filling loop, typically a braided flexible hose with two valves located underneath or alongside the boiler. Open both valves slowly and watch the pressure rise to around 1.2 bar, then close both valves firmly. If you are not confident, leave it - it takes an engineer about five minutes.

Check for a frozen condensate pipe. During cold spells across Wiltshire, a frozen condensate pipe is one of the most common reasons boilers stop working. This is a white or grey plastic pipe, usually 32mm in diameter, that exits the boiler and runs outside through an external wall. If it has frozen solid, the boiler will lock out. You can thaw it yourself by pouring warm (not boiling) water over the external section. Once thawed, reset the boiler.

Check whether nearby properties are affected. If several homes in your part of Corsham are without heating, there may be a wider network issue. Check the Cadent Gas website or give them a quick call before booking a private engineer.

At this stage, running a check through the Voltrade GoFIX diagnostic tool is worth doing - it walks through the most likely causes based on your boiler make, model, and symptoms, and helps you decide whether this is a same-day emergency or something that can safely wait until morning.

Same day

Once you have established the boiler needs a professional, the same day is about getting the right person booked and preparing properly for their visit.

Book a Gas Safe registered engineer. In the UK, it is a legal requirement that anyone working on gas appliances holds Gas Safe registration. You can verify any engineer's credentials at gassaferegister.co.uk using their licence number. Any engineer who cannot provide a Gas Safe ID should not be touching your boiler.

When you call to book, have the following ready:

• Boiler make and model (printed on the front panel)
• The fault code if there is one on the display
• Approximate age of the boiler
• Whether hot water is also affected, or just heating

This information helps the engineer anticipate which parts to bring. Many Corsham call-outs involve a second visit purely because a component was not anticipated and is not in stock.

Sort temporary heating. If you have young children, elderly residents, or a cold week ahead, pick up an oil-filled radiator or fan heater for the main living spaces. Decent options are available for between 20 and 50 pounds at most hardware shops, and they're worth keeping anyway.

The repair visit

A boiler diagnostic visit from a Gas Safe engineer in the Corsham area typically costs between 80 and 120 pounds for the call-out and initial diagnosis, with many engineers including the first hour of labour in that figure.

The engineer will start with the same checks described above, then go deeper. They will test the ignition system, inspect the gas valve, check the heat exchanger, examine the flue, and assess the PCB (the boiler's control board). A thorough diagnosis typically takes 30 to 60 minutes.

Common faults and typical repair costs in 2026 (parts and labour combined):

• Igniter or electrode replacement: typically 100 to 180 pounds
• Flame sensor or thermocouple: typically 80 to 150 pounds
• Gas valve replacement: typically 200 to 350 pounds
• Diverter valve: typically 150 to 250 pounds
• Pump replacement: typically 150 to 280 pounds
• Printed circuit board (PCB): typically 250 to 450 pounds depending on the model

If the boiler is over 10 to 12 years old and needs a major component like a PCB or heat exchanger, your engineer may recommend replacement over repair. A new combi boiler fitted in a Wiltshire property typically costs between 2,000 and 3,500 pounds including installation, depending on the model and the complexity of the pipework. Worcester Bosch, Vaillant, and Ideal are consistently reliable choices for long-term performance.

For the more common faults with a part in stock, the full repair can usually be completed within two to three hours.

The following week

Once the boiler is running again, keep an eye on it for the next few days rather than assuming everything is fine.

Monitor the pressure. Check the gauge every couple of days. If it keeps dropping below 1 bar, you likely have a slow leak somewhere in the system - at a radiator valve, a pipe joint, or possibly an expansion vessel that needs attention. A single pressure drop immediately after a repair is sometimes normal as air moves through the system. A consistent pattern is not.

Bleed your radiators. If radiators in your Corsham home are cold at the top but warm at the bottom, there is trapped air in them. Bleeding takes five minutes and a radiator bleed key. Do this with the heating running, then check and re-pressurise if needed.

Test the thermostat properly. Dial the thermostat up and down and confirm the boiler responds promptly. If it is sluggish or fails to fire at lower set temperatures, the thermostat may need replacing - a relatively minor job in most cases.

Watch for returning fault codes. If the boiler locks out again in the same week for the same code, contact your engineer. The repair may not have fully addressed the underlying issue, and it is better to flag this while the visit is recent.

Long term

A boiler that has failed once is more likely to fail again if the root cause was a symptom of broader wear rather than an isolated incident. Treating the boiler like a car - with regular servicing, not just emergency attention - is the most reliable way to avoid being without heating in a Corsham winter.

Annual boiler service. A Gas Safe registered engineer should service your boiler once a year. This costs typically between 80 and 120 pounds and involves cleaning components, checking gas pressures, inspecting the flue and seals, and catching early signs of wear before they develop into breakdowns. Many homeowners across Wiltshire skip this and end up paying considerably more when something fails mid-winter.

Boiler cover plans. A monthly cover plan can make sense, particularly for older boilers. These typically cost between 15 and 35 pounds per month and cover call-outs and parts. Read the exclusions carefully - many plans exclude pre-existing faults or boilers beyond a certain age.

Consider a power flush. If your boiler has been struggling or your radiators have persistent cold spots, a power flush clears sludge and debris from the entire system. Costs typically run from 400 to 600 pounds for an average-sized home, but extending the life of the boiler and radiators often makes it worth doing.

Think about boiler age. Modern condensing combi boilers run at over 90% efficiency. If yours pre-dates 2005, you are likely spending considerably more on gas than you need to. Replacement is not cheap, but the efficiency savings combined with improved reliability typically make the case over a three to five year window.

Timeline questions

How long does it take to fix a boiler that won't fire up?

It depends on the fault. A frozen condensate pipe or low pressure issue can be resolved in under an hour. A faulty igniter or gas valve, assuming the part is in stock, typically takes two to three hours. A PCB or heat exchanger replacement can take a full day. Your engineer should give you a realistic time estimate once they have completed the initial diagnosis.

Can I do anything myself when my boiler won't fire?

Yes, a few things. Repressurising the system, resetting the boiler, and thawing a frozen condensate pipe are all safe DIY actions for a competent homeowner. Anything involving internal gas components, the gas valve, or the flue must be carried out by a Gas Safe registered engineer. Attempting gas work without registration is illegal under UK law and carries serious safety risks.

Why does my boiler keep failing to ignite even after a reset?

Repeated ignition failure typically points to a faulty igniter electrode, a problem with the gas valve, or a dirty or failing flame sensor. In some cases, a weak or intermittent gas supply can also cause repeated lockouts. Each of these requires a Gas Safe engineer to diagnose and repair correctly. Continuing to reset the boiler without investigation can mask a worsening fault.

How much does an emergency boiler repair in Corsham cost?

Emergency call-outs, particularly evenings and weekends, typically carry a higher charge than standard daytime appointments. Expect to pay between 100 and 180 pounds for the call-out and first hour of labour on an emergency basis, with parts charged on top. If the situation can safely wait until the next working day, you will commonly save 30 to 50 pounds or more on the call-out charge alone.