Is your boiler or central heating system playing up? The good news is that not every boiler problem means disaster. Some faults are straightforward and safe to check yourself, while others must be checked by a Gas Safe engineer. And some might indicate that your boiler is reaching the end of its life.
In this guide, we’ll walk through the most common boiler problems, what they usually mean and what to do next. We’ll also explain what you can safely check yourself at home, and when it’s time to call in a professional.
For urgent boiler servicing and repairs, or to enquire about a new boiler, contact JPS Plumbing, Gas and Electrical. Our experienced local team covers Winchester, Southampton and the surrounding Hampshire areas.
Boiler troubleshooting: what to check first
Boiler issues often start with small warning signs such as unusual noises, pressure drops, intermittent heating or recurring fault codes. Catching problems early can sometimes prevent more serious and expensive repairs later on.
What you can safely check yourself
Before calling an engineer, there are a few sensible checks that most homeowners can safely make. The following is just a brief guide. Be sure to consult your boiler manufacturer’s instruction manual before carrying out any of these checks, and always call a professional if you’re unsure where anything is or how it works.
Boiler pressure
The pressure gauge is on the front of the boiler, usually near the bottom or on the control panel. Some newer boilers have digital displays, while a traditional pressure gauge is a small, round dial. If your boiler’s pressure gauge shows below 1 bar, top it up using the filling loop until it reaches around 1–1.5 bar.
Thermostat settings and batteries
Make sure the thermostat is turned up high enough and replace the batteries if the screen is blank or unresponsive.
Power supply and fused spur (boiler switch)
Switch on the fused spur, which looks like a normal switch, located on the wall near the boiler. If the boiler display is blank, check your fuse box too, in case a switch has tripped.
Reset the boiler
If your boiler is locked out or showing an error code, consult the troubleshooting section of your boiler manual. Follow the instructions, and if it doesn’t work, press the reset button, then wait a few minutes until it restarts. If the problem persists, don’t keep resetting it – leave it as is and arrange an inspection.
See if the condensate pipe has frozen
Look outside for a white plastic pipe coming from the boiler. In cold weather, this can freeze, blocking wastewater and causing the boiler to shut itself down as a safety precaution. Thaw the pipe gently with warm water (not boiling), or hold a hot water bottle against it.
Bleed the radiators
If a radiator is warm at the bottom but cold at the top, or you hear unusual gurgling, there may be air in the system. Look for the small bleed valve at the top corner of the radiator. You’ll need a radiator key, available from DIY shops or plumbers’ merchants. To release trapped air, turn the valve slowly until the hissing stops and a little water appears, then close it again.
When to call a Gas Safe registered engineer
Never attempt to dismantle a boiler or any other gas appliance yourself. If you have been through the troubleshooting list above and your boiler is still not working as it should, then call an engineer.
You should contact a Gas Safe-registered boiler engineer straight away if:
- The boiler repeatedly shuts down
- Water is leaking from the boiler, especially if it’s heavy, near electrics, or causing pressure to drop
Call the National Gas Emergency Service number on 0800 111 999 as soon as possible if:
- You smell gas
- You suspect a carbon monoxide leak. Signs include soot marks and yellow flames. Symptoms of carbon monoxide poisoning can include headaches, dizziness, nausea, shortness of breath, or feeling unusually tired indoors. If you suffer any of these symptoms, get outside immediately and leave doors and windows open.
10 common boiler problems – symptoms, potential causes and what to do next
Here are 10 of the most common boiler fault questions we hear from our customers. Drawing on years of experience repairing, servicing and installing boilers, we’ll explain what the symptoms might mean, what you can safely check yourself, and when it’s time to call in an expert.
1. Why is my boiler not firing up?
Symptoms:
The boiler won’t start at all, there’s no heating or hot water, or the display is blank or showing a fault light.
Potential causes:
This can be something simple, like a tripped switch, flat thermostat batteries, low pressure or a frozen condensate pipe after a cold night. On older boilers, it may also be an issue with the pilot light or ignition system. If other gas appliances aren’t working either, the issue may be with the gas supply rather than the boiler itself.
What to do next:
Check the power, pressure and thermostat first. If the weather is cold, check if the condensate pipe is frozen, and if so, pour warm water on it to thaw it out. If the boiler keeps trying to fire up and failing, or locks out again after resetting, there’s usually an underlying fault, so you’ll need to call an engineer.
2. Why do I have no heating or hot water?
Symptoms
You may have no heating, no hot water, or one working while the other does not.
Potential causes
If both have stopped, the boiler may not be firing properly. If you have heating but no hot water, or hot water but no heating, it could point towards a diverter valve issue, especially on a combi boiler. Older systems may also struggle with pumps, valves or general wear when demand is high.
What to do next
Check the boiler pressure and thermostat settings first. If the problem keeps returning or the hot water has become unreliable over time, it’s worth getting it checked before the system fails completely.
3. Why are my radiators cold even though the boiler is working?
Symptoms
The boiler seems to be running, but some or all radiators stay cold, heat unevenly, or have cold spots.
Potential causes
If radiators are cold at the top, trapped air is usually the culprit. If they’re cold at the bottom, sludge or limescale build-up may be restricting circulation. We see this quite a bit in older central heating systems that haven’t been flushed or maintained for years.
What to do next
Bleeding the radiators is the best place to start. If the same radiators keep going cold, or the whole heating system feels sluggish, there may be a deeper circulation issue. In some cases, a professional power flush can help remove sludge and improve how the system heats up.
4. Why is my boiler losing pressure?
Symptoms
The pressure gauge keeps dropping below 1 bar, the heating cuts out, or you have to keep topping the boiler up.
Potential causes
Low boiler pressure after bleeding radiators is fairly normal. If your system is regularly losing pressure, it usually means it’s losing water somewhere, either through a small leak, a worn seal, a pressure relief valve problem, or an expansion vessel issue.
What to do next
Top the system up using the filling loop. But if you’re doing that every few weeks, don’t ignore it. On older boilers, recurring pressure issues can sometimes point to wider wear in the system.
5. Why is my boiler making strange noises?
Symptoms
You hear gurgling, banging, whistling, kettling or vibrating noises from the boiler or radiators.
Potential causes
Gurgling is often trapped air. Whistling or kettling usually points towards limescale or sludge restricting water flow. Banging can be more concerning and may mean the system is overheating or struggling to circulate water properly.
What to do next
Bleeding the radiators may help if air is trapped. If the noises are getting louder, more frequent or affecting performance, it’s better to deal with it early rather than wait for a more expensive fault.
6. Why is my boiler leaking water?
Symptoms
You notice water under the boiler, damp marks nearby, rust, corrosion or pressure dropping regularly.
Potential causes
Sometimes it’s a worn seal or loose connection. Other times, leaks are caused by corrosion, excess pressure or internal component failure. A lot depends on the age and condition of the boiler.
What to do next
Switch the boiler off and call an engineer. It’s important not to delay, as even a small drip can cause damage over time, and can be dangerous if it’s near electrics.
7. Why does my boiler keep switching off or showing fault codes?
Symptoms
The boiler locks out, switches itself off, displays an error code, or cuts in and out unexpectedly.
Potential causes
Modern boilers often shut themselves down when something isn’t right, such as low pressure, a blockage, a sensor fault, overheating, ignition problems or heat exchanger issues.
What to do next
Check the manual for the fault code and reset the boiler once, if advised to do so. If the same fault keeps coming back, don’t keep pressing reset. There’s nearly always a reason behind it.
8. Have I got a faulty thermostat?
Symptoms
The heating doesn’t come on when expected, cuts off too early, ignores the temperature setting, or feels inconsistent.
Potential causes
This is often simpler than people think. The batteries may be flat, the settings may have been knocked, or the thermostat may have lost connection to the boiler. Older controls can also become unreliable over time.
What to do next
Check the settings and replace batteries first. If the heating still has a mind of its own, the controls may need repairing, replacing or upgrading.
9. Why is my boiler working intermittently?
Symptoms
The boiler works fine one minute and stops the next, making the issue difficult to pin down.
Potential causes
Intermittent faults are often linked to ageing electrical components, worn sensors, pump issues or overheating problems that only appear under certain conditions.
What to do next
If it happens once, keep an eye on it. If it becomes a regular occurrence, get ahead of it and arrange an inspection. Intermittent faults often worsen over time, and they have a habit of turning into full breakdowns when you need the boiler most.
10. Why does my boiler keep needing to be reset?
Symptoms
You keep pressing reset to get the heating or hot water working again.
Potential causes
An occasional reset after a power cut is one thing. Repeated resets usually mean the boiler is detecting an ongoing fault, such as ignition trouble, overheating, pressure issues, sensor faults or a failing PCB.
What to do next
Don’t let resetting become part of the routine. If the boiler keeps locking out, it needs a proper diagnosis. Sometimes the repair is straightforward, but repeated lockouts can also be an early sign that the boiler is becoming unreliable and might need replacing.
How do I know if I need a new boiler?
Not every boiler problem means you need a replacement. Plenty of faults, such as low pressure, thermostat issues, or minor leaks, can often be repaired cost-effectively, especially if you have a newer-style condensing boiler that has been well maintained.
Replacement starts to make sense when the same problems keep recurring, or if your boiler is nearing the end of its 10–15-year lifespan. At that point, it becomes a cost-versus-value decision, i.e., how much are you spending to keep it going, and how many reliable years are you likely to get back?
It may be time to consider a new boiler if the parts are becoming hard to source, your energy bills are rising, or your heating and hot water are no longer dependable. A modern boiler can improve efficiency, save you money, and provide more consistent performance. It will also come with a brand new warranty for added protection.
For a fuller breakdown, read our guide to when a boiler is considered beyond economical repair.
Reliable boiler repair, servicing and installation in Hampshire
If your boiler isn’t working properly, JPS Plumbing, Gas and Electrical is here to help. We’re trusted Gas Safe-registered engineers for Winchester, Southampton, and the surrounding Hampshire areas.
We offer reliable boiler maintenance, repairs and servicing to keep your boiler running smoothly. We can also give you clear, honest advice on when to consider a new boiler.
No jargon. No pressure. Just practical help from experienced local engineers.
Call us today on 01962 448013 or 02381 733139, or send us a message online.