Boilers rarely fail without warning. They give you signals for weeks or months first. These are the five worth acting on before the weather turns.
Breakdowns have a habit of arriving just when you need the heating most, in the first properly cold spell. Many of the winter breakdowns we are called to could have been prevented by a service in the autumn. Whether you own your home or let it out, spotting these signs early saves money, stress and cold nights.
1. It is making noises
Banging or clunking, whistling, gurgling, or a low vibrating hum.
Noise almost always means limescale or sludge restricting water flow. West Sussex and Surrey are hard water areas, so scale build-up is common here.
Kettling in particular reduces efficiency and puts real thermal stress on components. Left alone it can crack a heat exchanger, which turns a cleanable problem into a replacement boiler.
What to do: book a service so a Gas Safe engineer can find the cause. If it turns out to be sludge or scale, a powerflush clears the system and restores proper flow. Our guide to boiler noises explains what each sound usually means.
2. Your bills are climbing
If your gas bills have risen without a matching change in how much heating you use, the boiler is working harder than it should.
Causes are reduced efficiency with age, sludge reducing heat transfer, faulty components forcing longer run times, and poor combustion from dirty burners.
The scale of this surprises people. A boiler that was ninety percent efficient when new can be down to sixty or seventy percent after twelve years without maintenance. On a typical heating bill that is hundreds of pounds a year going nowhere.
What to do: this is exactly what an annual service is for. The engineer cleans the components, tests the combustion and adjusts the settings so the boiler burns no more gas than it needs to. A boiler service is from £105, which is small next to the cost of a boiler burning more gas than it should.
3. The flame is yellow instead of blue
This one is a safety issue rather than an efficiency one.
A correctly burning gas boiler has a crisp blue flame. Yellow or orange means incomplete combustion, and incomplete combustion produces carbon monoxide, which is odourless and lethal.
If you see this: turn the boiler off, open windows, and call a Gas Safe engineer urgently. Do not use it until it has been inspected.
Every service should include a carbon monoxide check as standard. The engineer also checks the flame and the combustion readings, which is how a problem like this gets caught before it becomes dangerous.
If a carbon monoxide alarm goes off, open doors and windows, get everyone outside into fresh air, and call the National Gas Emergency Service on 0800 111 999.
4. You are topping up the pressure regularly
Normal is a slight drop once or twice a year, usually after bleeding radiators.
A problem is pressure dropping weekly or needing constant attention. That means a leak somewhere: a radiator valve, a pipe joint, the boiler itself, a passing pressure relief valve, or a failed expansion vessel.
As a rule of thumb, if you are topping up more than once a month, something is wrong. One more cause is worth knowing about: an automatic air vent that lets water out along with the air it is meant to release.
Topping it up manages the symptom. Finding the leak is the fix.
Not every leak is visible. Leak detection finds hidden leaks under floors and behind walls without unnecessary damage to the property. Our guide to a boiler losing pressure covers the checks you can make first.
5. It is over eight years old and has not been serviced
Components degrade, efficiency drops, and breakdown rates rise sharply after eight to ten years. Parts also start becoming scarce on older models.
Service it if it is under ten years old, has been maintained reasonably, is running acceptably and has no major fault.
Consider replacing it if it is over fifteen, breaking down repeatedly, expensive to run and facing a costly repair.
Modern boilers are significantly more efficient. A new boiler can cut heating costs by twenty to thirty percent compared with a fifteen year old model, so on an old boiler facing a big repair, that saving belongs in the sum. Our guide to repairing or replacing a boiler sets out how to decide.
What a service actually covers
- Visual inspection for leaks, corrosion and damage
- Flue gas combustion analysis to confirm it is burning correctly
- Cleaning the burner, heat exchanger and condensate trap
- Testing every safety device
- Gas pressure and flow checks
- Carbon monoxide testing
- System pressure and inhibitor levels
You should get the actual readings in writing, not just a sticker on the casing.
If you are a landlord, remember that a service and a gas safety certificate are different things. A rented property needs the gas safety check every year by law, and the service is what keeps the boiler reliable and its warranty valid. It makes sense to book both at the same visit.
Frequently asked
How often should a boiler be serviced?
Annually. Nearly every manufacturer guarantee requires it, and skipping a year is the single most common reason an otherwise valid warranty claim gets declined. For landlords, an annual gas safety check is a legal requirement on top of that.
Can I service my boiler myself?
No. Only Gas Safe registered engineers can legally work on gas boilers. Beyond the legality, the checks that matter, such as flue gas combustion analysis, need equipment and training.
What is actually done during a service?
Gas pressure and flow checked, a full flue gas combustion analysis, burner and heat exchanger inspected and cleaned, condensate checked, all safety devices tested, system pressure and inhibitor levels verified, and the flue checked for soundness. You get the readings in writing.
How much does a boiler service cost?
Our boiler service is from £105, at a fixed price with no hidden extras. If you are a landlord, combining it with a gas safety certificate works out cheaper than booking the two separately.
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Relevant in:CrawleyHorshamHaywards Heath