Common Boiler Error Codes Explained for Andover Homeowners

Published September 2026 | Boiler Repair

In the First 10 Minutes

Your boiler has locked out and there's a code on the display. Before anything else, stay calm. In most cases, a fault code is a diagnostic message, not a crisis. The boiler has done its job by shutting itself down safely rather than carrying on and causing a bigger problem.

The first thing to do is write down the exact code - brand and model included. F22 on a Vaillant means something completely different from F22 on a Baxi. The brand is everything. Check the label on the front panel if you're not sure what you're dealing with.

Then run through this quick safety check before you do anything else:

1. Can you smell gas? If yes, do not touch the boiler. Leave the house, keep doors open, and call the Gas Emergency Helpline on 0800 111 999. Do not use light switches or your phone inside the property.
2. Is there water on the floor around the boiler or nearby pipework? Turn off the water supply at the stopcock and call a Gas Safe registered engineer.
3. No gas smell, no water, just a locked-out display? You may be able to reset safely.

To reset, press the button marked with a flame symbol or the word "Reset" - usually for around 3 seconds. If the boiler fires and runs normally, monitor it for the next hour. If the same code comes straight back, leave it locked out and get an engineer booked in.

Within the First Hour

Once you've done the immediate checks, the next step is identifying what the code actually means. Here's what our engineers see most commonly in Andover homes.

Low pressure codes show up as F22 on Vaillant, F1 on Worcester Bosch, L1 on Ideal, and E119 on Glow-worm. Your pressure gauge should read between 1 and 1.5 bar when cold. If it's sitting below 1, you may be able to repressurise yourself using the filling loop - a silver or grey flexi-hose under the boiler. Turn both valves slowly until the gauge reaches 1.2 bar, close them, and reset. If the pressure holds, you're likely fine for now. If it keeps dropping, there's a leak somewhere and that needs a professional.

Ignition failure codes appear as F28 and F29 on both Vaillant and Worcester Bosch, E1 and E2 on Baxi, and L2 on Ideal. First check whether your hob or gas fire lights. If your other gas appliances aren't working either, there may be a supply issue in your area - check with your gas supplier. If everything else runs fine, the fault is internal.

Overheat codes include E9 on Worcester Bosch, F75 on Vaillant, and E1 on Ideal. These mean the boiler got too hot and shut down as a safety measure. This can come from a blocked heat exchanger, a failing pump, or poor flow through the system. Do not keep resetting an overheat code - you can damage the heat exchanger, which is one of the most expensive components on any boiler.

If you're unsure what your code means, the Voltrade GoFIX diagnostic tool lets you enter your brand and fault code and get a plain-English explanation along with a severity rating - useful for deciding whether you need emergency help or can wait until the next morning.

Same Day

If the boiler won't restart, or it's mid-winter and you're without heating or hot water, getting an engineer booked the same day becomes the priority.

When you call, have the following ready:

1. The boiler make and model (on the label inside or on the front panel)
2. The exact error code
3. How long it's been faulting
4. Whether it's happened before
5. Whether you've already reset it, and how many times

This saves time on the call and means the engineer can often bring the right parts on the first visit. In Hampshire generally, same-day call-out fees typically run between 80 and 150 pounds, depending on time of day and travel distance. Out-of-hours emergency rates are higher - expect to pay 100 to 200 pounds for the call-out alone before any parts are included.

Before booking, check whether your boiler is still under manufacturer warranty. Worcester Bosch, Vaillant, and Ideal all offer 2 to 5 years as standard, and some offer extended warranties. An unauthorised repair by a non-approved engineer can void it, so check your paperwork first.

If the boiler is over 10 years old and you've had recurring codes over the past year, it's worth raising the repair versus replacement question with the engineer. A heat exchanger replacement on an older Baxi or Ideal can cost 400 to 700 pounds - getting close to the cost of a new budget boiler on a simple installation.

The Repair Visit

Gas Safe registration is a legal requirement for any engineer working on a gas boiler in the UK. This isn't optional - it's the law, and it exists because combustion faults can kill. Always check the engineer's Gas Safe ID card when they arrive. You can also verify registration at the Gas Safe Register website before booking.

When the engineer arrives at your Andover property, they'll typically start with a visual inspection and system pressure check, then connect a flue gas analyser to assess combustion efficiency. For intermittent faults, they'll ask you to describe exactly when the code appeared - during a call for hot water, central heating, or both. That context matters.

Typical repair times and costs for the faults most common in Andover:

• Repressurise and filling loop repair: 30 to 60 minutes, typically 80 to 150 pounds including call-out
• Ignition electrode or lead replacement: 1 to 2 hours, typically 120 to 200 pounds
• Gas valve replacement: 1.5 to 3 hours, typically 200 to 400 pounds
• Pump replacement: 1 to 2 hours, typically 150 to 300 pounds
• PCB replacement: 1 to 2 hours, typically 200 to 500 pounds depending on the boiler brand and model
• Heat exchanger replacement: 3 to 5 hours, typically 400 to 800 pounds

Parts prices vary considerably by brand. Vaillant and Worcester Bosch parts tend to cost more than Ideal or Baxi equivalents, but they're usually more widely stocked, which matters when you need a same-day fix in the middle of January.

The Following Week

After the repair, keep an eye on the pressure gauge for a few days. A properly sealed system should hold steady at around 1 to 1.5 bar. If you're topping it up more than once a month, there's a slow leak somewhere that needs to be found and fixed.

Run both hot water and central heating for a full cycle - roughly 30 to 45 minutes on heating. Check that every radiator is getting warm from top to bottom. Cold spots at the top suggest trapped air, which you can bleed out with a radiator key. Cold spots at the bottom or on one side typically indicate sludge build-up, which is a job for a power flush rather than a bleed.

If the same fault code comes back within seven days, contact the engineer. Most reputable Hampshire engineers include a short-term guarantee on their work - commonly 30 to 90 days on parts and labour. It's worth asking before the job starts so there's no ambiguity if you need them back.

Long Term

Annual servicing is the most effective thing you can do to avoid fault codes and emergency call-outs. A Gas Safe engineer will clean the burner, check combustion readings, inspect all seals and sensors, and pick up on small issues before they trigger lockouts. Services in the Andover area typically cost between 60 and 100 pounds - a fraction of even the most minor call-out repair.

If your system doesn't already contain a central heating inhibitor, ask your engineer to add one at the next service. This chemical prevents corrosion and sludge build-up inside the pipework and radiators - two of the most common causes of pump failure and heat exchanger blockages.

For boilers more than 12 years old with a history of recurring codes, the honest engineering assessment is usually that ongoing repair costs will outpace the investment in a replacement within 3 to 5 years. Modern condensing boilers from Worcester Bosch, Vaillant, and Viessmann typically achieve efficiency ratings above 90%, which translates directly into lower gas bills. A new A-rated boiler installed in an Andover property typically costs between 1,800 and 3,500 pounds depending on boiler size, flue configuration, and any changes to existing pipework. Many manufacturers now offer extended warranties of up to 10 years when the installation is carried out by an approved engineer.

Timeline Questions

How do I know if my boiler error code is an emergency?

Any fault code accompanied by a gas smell is always an emergency - call 0800 111 999 immediately and get everyone out of the property. Overheat codes such as E9 or F75 should be treated as urgent because repeated resets risk damaging the heat exchanger. Low pressure codes are rarely dangerous but will leave you without heating or hot water until fixed. Ignition failure codes sit somewhere in between - aim to get them looked at within 24 hours rather than leaving it for days.

Can I reset my boiler myself or do I need a Gas Safe engineer?

You can press the reset button yourself - that doesn't require Gas Safe registration. What you cannot legally do is open the casing, adjust the gas valve, or touch anything inside the combustion chamber. If a single reset clears the fault and it doesn't return, you may be absolutely fine. If the same code comes back more than twice in quick succession, stop resetting it. You're masking a fault that's likely getting worse each time the boiler fires.

How much does a boiler repair typically cost in Andover?

Minor repairs like thermostat replacement or a repressurisation job typically come in at 80 to 150 pounds all-in. Mid-range repairs such as pump or gas valve replacements typically run between 150 and 400 pounds. Major components like a PCB or heat exchanger can reach 400 to 800 pounds depending on the brand. Always get a written quote before authorising work, and for non-urgent repairs it's worth comparing two or three quotes from Gas Safe engineers covering the Hampshire area.

What does it mean if my boiler keeps showing the same fault code after being repaired?

A recurring code after a repair usually points to one of three things: the wrong component was replaced, the root cause was misdiagnosed, or there's a secondary fault that wasn't picked up during the first visit. Go back to the original engineer first - most will return under their workmanship guarantee. If the fault comes back after a second visit, get a second opinion from a different Gas Safe engineer in the Andover area before agreeing to any further parts expenditure.