Boiler Not Firing Up in Petworth? Common Causes and What to Do Next

Published August 2026 | Boiler Repair

A homeowner in Petworth wakes up on a bitter January morning to find the radiators stone cold. She checks the thermostat, turns it up, waits. Nothing happens. The boiler makes a clicking sound, almost fires, then goes quiet. She tries resetting it twice, gets the same result, and by 8am she's standing in the kitchen in a coat wondering whether she's looking at a minor fix or a very expensive week. It's a situation our engineers see constantly across West Sussex, and in the vast majority of cases, there's a clear, diagnosable reason the boiler won't fire.

What Was Actually Going On

In this particular case, the homeowner had a Worcester Bosch Greenstar 30i combi boiler, about seven years old and generally well maintained. When our engineer arrived and ran a diagnostic using the Voltrade GoFIX tool, the fault code on the boiler's display pointed to an ignition lockout. The boiler was attempting to fire, the gas valve was opening, but the flame wasn't being detected - so the boiler was cutting out as a safety measure.

There are several distinct components involved in the ignition process, and any one of them can cause this exact symptom. Here's what the engineer checked, in order:

The Flame Sensor (Ionisation Electrode)

This is one of the most common culprits when a boiler clicks but won't fire. The flame sensor detects whether a flame has actually established after the gas valve opens. Over time, the electrode tip can become coated in carbon deposits, which prevents it from reading the flame signal correctly. The boiler assumes ignition has failed and locks out. On this Petworth property, the sensor was visibly contaminated - a classic sign of a boiler that had been running slightly rich, possibly due to a marginal gas valve issue.

The Gas Valve

Gas valves can fail in two ways - they either stop opening at all, meaning no gas reaches the burner, or they open but don't modulate correctly, leading to weak or unstable flames. A weak flame is enough to cause repeated lockouts because the flame sensor can't get a consistent reading. The gas valve on this boiler was still functional but was borderline - delivering gas, but not with enough consistency to hold a stable flame at ignition.

Boiler Pressure

Before anything else, our engineer checked the pressure gauge. Low pressure (typically below 1 bar on most domestic combi boilers) will prevent a boiler from firing. This is a protection mechanism - running a boiler with insufficient water pressure can cause serious damage to the heat exchanger. In this case, pressure was fine at 1.3 bar, so it wasn't the issue, but it's always the first thing to check.

The Condensate Pipe

Modern condensing boilers produce acidic condensate as a byproduct of their efficiency. This drains away through a plastic pipe, often routed outside. In cold weather, particularly in rural West Sussex where temperatures can drop sharply, this pipe can freeze solid. When it does, the boiler detects a blockage and shuts down. This wasn't the cause here - it was January but mild - but it's worth mentioning because a frozen condensate pipe accounts for a significant proportion of no-heat callouts during cold snaps.

The Printed Circuit Board (PCB)

If ignition components check out but the boiler still won't fire, the PCB - the brain of the boiler - comes under suspicion. PCB faults can cause almost any symptom, from failure to ignite to random lockouts to component misbehaviour. They're among the more expensive fixes and typically require replacement rather than repair. The PCB on this Petworth boiler was functioning correctly.

The diagnosis in this case came down to two things working together: a contaminated flame sensor giving inconsistent readings, and a gas valve that was on its way out. Either issue alone might have produced intermittent problems. Together, they were enough to prevent reliable ignition.

How the Problem Was Resolved

The engineer replaced the flame sensor first - a relatively quick job on the Worcester Bosch Greenstar range because the combustion chamber is reasonably accessible. He cleaned the surrounding area, checked the spark electrode while he was in there (it showed slight wear but was still serviceable), and tested ignition.

The boiler fired, but not cleanly. The flame established but flickered at startup in a way that confirmed the gas valve was the secondary issue. Rather than leave it and wait for a return visit in two weeks when the valve failed completely, the homeowner agreed to have the gas valve replaced on the same visit.

Gas valve replacement on a combi boiler requires the engineer to isolate the gas supply and work on the internal gas-carrying components. Under UK law, this work must only be carried out by a Gas Safe registered engineer. There's no grey area here - it's a legal requirement, and for good reason. An incorrectly fitted gas valve can leak, and a gas leak in a property is a serious safety risk. Always check that your engineer is on the Gas Safe Register before any gas component work begins. Our engineers carry their Gas Safe ID and you can verify them online at any time.

With both the flame sensor and gas valve replaced, the boiler fired cleanly on first attempt and held a stable flame across multiple start cycles. The heating and hot water both tested correctly, and the engineer ran the system for 20 minutes to confirm normal operation before leaving.

What This Cost and How Long It Took

This is where people in Petworth and across West Sussex often have questions, because boiler repair pricing can feel opaque. Here's what this job actually involved:

• Callout and diagnostic: typically between 60 and 90 pounds for most local engineers
• Flame sensor replacement (parts and labour): typically 80 to 150 pounds depending on boiler make and model
• Gas valve replacement (parts and labour): typically 200 to 350 pounds - gas valves are not cheap components, and the labour involves working on gas-carrying parts

In total, this job came to around 520 pounds including the diagnostic visit. That's towards the higher end for a single repair visit, but the homeowner was having two components replaced at once, which is almost always cheaper than two separate callouts weeks apart.

The whole job took just under three hours. That included arrival, diagnosis, parts retrieval from the van (the engineer carried the flame sensor in stock; the gas valve required a short wait while a parts run was arranged locally), and the full replacement and test procedure.

For context, if the issue had been solely a frozen condensate pipe - which our engineers see regularly during cold spells in Petworth and surrounding villages - the fix costs almost nothing. Thawing a condensate pipe takes 10 minutes and can often be done by the homeowner. At the other end of the scale, a failed PCB on a modern combi boiler can cost 400 to 600 pounds in parts alone, and at that point it often makes more financial sense to consider whether a boiler replacement is the better long-term investment.

How to Spot the Same Issue in Your Home

A boiler that won't fire tends to present in fairly recognisable ways. Here's what to look for, in order of what to check yourself before calling an engineer:

1. Check the pressure gauge. This is the first thing any engineer will ask you. It's usually a small dial or digital display on the front of the boiler. It should read between 1 and 1.5 bar when the system is cold. Below 1 bar, you'll need to repressurise via the filling loop. Above 3 bar, the pressure is too high and the boiler may have locked out for that reason.
2. Check for a fault code. Modern boilers display error codes when they lock out. Look these up in your boiler manual or search the exact model number and code - Worcester Bosch, Vaillant, Ideal, Baxi, and Viessmann all publish fault code guides online. The Voltrade GoFIX diagnostic tool can also read live fault codes remotely on compatible boilers, which can save you a diagnostic callout fee.
3. Try a reset. Press the reset button (usually marked with a symbol that looks like a circle with a line) and wait. The boiler will attempt to fire. If it fires and holds, great - but note that if it locks out again within a day or two, there's an underlying fault that won't go away with resets alone.
4. Check the condensate pipe. If it's freezing weather and your condensate pipe runs outside, feel along it carefully. If it's frozen solid, you can carefully pour warm (not boiling) water over the exterior section to thaw it. Once thawed, reset the boiler.
5. Check your gas supply. Turn on a gas hob ring. If that won't light either, the issue is with your gas supply, not your boiler - contact your gas supplier or National Gas on 0800 111 999 if you suspect a supply interruption.
6. Listen to the ignition attempt. A boiler that clicks repeatedly but doesn't fire suggests the spark is there but the gas isn't arriving (gas valve issue) or the flame isn't being detected (flame sensor issue). A boiler that makes no sound at all after reset suggests an electrical or PCB issue. A boiler that fires briefly and then cuts out quickly is often a flame sensor or gas valve problem.

If you've been through this list and the boiler still won't fire, it's time to call a Gas Safe registered engineer. Don't keep resetting a boiler that persistently locks out - it's doing that for a reason, and ignoring the underlying cause rarely ends well.

What Every Petworth Homeowner Should Know

Properties in Petworth and the surrounding villages vary enormously in age and heating setup. There are converted period properties with ageing systems that were last serviced years ago, and newer builds with modern condensing combi boilers. The advice below applies across the board, but it's especially relevant if your boiler is more than 10 years old.

Annual Servicing Is Not Optional

A boiler service - carried out by a Gas Safe registered engineer - typically costs between 80 and 120 pounds per year. During a service, the engineer cleans the burner and heat exchanger, checks the flame sensor and ignition electrodes, tests gas pressure and combustion, and inspects the flue. Most ignition failures that result in a cold house in January are preventable through regular servicing. The engineer working on this Petworth boiler noted that the last service sticker was dated three years prior - which is exactly the kind of gap that allows components to degrade to the point of failure.

Know Your Boiler Make and Model

Write down your boiler make, model, and serial number and keep it somewhere accessible. When you call an engineer, this information means they can identify likely fault codes before arriving, potentially bring the correct parts with them, and give you a more accurate estimate. Worcester Bosch, Vaillant, and Ideal are among the most common makes our engineers encounter across West Sussex, and parts availability for these tends to be good. Older or less common brands can mean delays while parts are sourced.

Older Boilers Reach a Point of Diminishing Returns

This is something our engineers discuss regularly with homeowners in Petworth and across the region. A boiler over 15 years old that's starting to develop faults is worth a frank conversation about total cost of ownership. If repair costs are approaching or exceeding a third of the cost of a new boiler, and especially if efficiency ratings are low (anything below an A rating), replacement often makes more financial sense than continued repair. A new A-rated condensing combi boiler from a brand like Vaillant or Worcester Bosch, installed by a Gas Safe registered engineer, typically costs between 2,000 and 3,500 pounds for a standard domestic installation - but it comes with a manufacturer warranty, modern efficiency, and years of reliable service ahead.

Don't Ignore Warning Signs Before the Full Failure

In the weeks before the full lockout, this homeowner had noticed the boiler sometimes took two or three attempts to fire in the morning, and that the hot water occasionally ran lukewarm for the first minute before reaching temperature. Both of these are textbook signs of an ignition system that's struggling. Catching it at that stage and booking a service would likely have meant a cheaper repair than a full emergency callout on a cold January morning. If your boiler is behaving oddly - taking longer to fire, producing inconsistent hot water temperatures, or locking out occasionally and then recovering - get it looked at sooner rather than later.

Related Questions

Why does my boiler keep clicking but not firing?

Repeated clicking without ignition typically means the spark electrode is working but the flame isn't establishing. The most common reasons are a faulty gas valve not delivering sufficient gas, a contaminated or failed flame sensor, or occasionally a blocked burner. It can also happen if gas pressure to the property is unusually low. If resetting the boiler doesn't resolve it and the issue returns, an engineer needs to check the ignition components directly - this is not a fault that resolves itself over time.

Can I fix a boiler that won't fire myself?

You can safely carry out a limited number of checks yourself - verifying the pressure, resetting the boiler, thawing a frozen condensate pipe, and checking your gas supply via another appliance. Beyond that, any work involving the internal components of a gas boiler must be carried out by a Gas Safe registered engineer. This is a legal requirement under the Gas Safety (Installation and Use) Regulations 1998, not just a recommendation. Attempting gas component work without registration is illegal and dangerous.

How much should I expect to pay for a boiler ignition repair in West Sussex?

Costs vary depending on which component has failed. A flame sensor replacement typically runs between 80 and 150 pounds parts and labour. A gas valve replacement is more significant, usually between 200 and 350 pounds. A PCB replacement can reach 400 to 600 pounds depending on the boiler model. Callout and diagnostic fees are typically 60 to 90 pounds on top. Always get a written quote that itemises parts and labour before authorising work. Some companies include the diagnostic in the repair cost if you proceed - worth asking upfront.

How do I know if my boiler needs replacing rather than repairing?

A useful rule of thumb is to compare the repair cost against the age and likely remaining lifespan of the boiler. If a repair costs more than 400 to 500 pounds on a boiler that's 12 or more years old, or if you've needed repairs multiple times in the last couple of years, replacement is often better value. An engineer can give you an honest assessment - ask them directly whether they'd repair or replace in your position. A good engineer will tell you straight, even if the more profitable answer for them would be a repair.