Common Boiler Faults: What's Going On and What You Can Do

Most of the calls we get at EK Plumbing & Heating follow the same patterns. A lot of boiler problems aren't as complicated as they first appear, and in many cases there are a couple of checks worth trying before calling anyone out. This guide isn't about encouraging DIY on anything gas-related. It's about helping you understand what you're looking at before you pick up the phone, and knowing when you absolutely need to.

No Heating or No Hot Water

The most common call-out, and also the one most likely to have a straightforward explanation. Start with the basics: check the pressure gauge (it should sit around 1 to 1.5 bar when cold), check your programmer or timer settings, and make sure the thermostat is set high enough to actually trigger the boiler. A tripped fuse or an isolation switch knocked off by accident can cause this too, and it's easy to overlook.

If none of that changes anything, the fault is likely internal. A faulty diverter valve is one possibility, as is a frozen condensate pipe or a temperature sensor that's given up. What the engineer will be looking for at that point depends on the boiler, its age, and what error code it's showing, so the more information you can give when you call, the better.

Low Boiler Pressure

The pressure gauge sits below 1 bar, radiators are barely warming up, or there's an error code on the display. This is one of the more straightforward faults to identify. Pressure drops when radiators have been bled recently (air isn't the only thing that comes out), when there's a small leak somewhere on the system, or when the pressure relief valve is discharging water it shouldn't be.

Topping up the pressure using the filling loop is something most people can manage at home. Your boiler manual will walk you through it. If the pressure keeps dropping within a few days of re-pressurising, there's a leak somewhere that needs tracking down. That's not something to leave alone.

Water Leaking From the Boiler

Water around the boiler can come from corroded pipework, worn seals, an over-pressurised system, or a failing heat exchanger. Some of these are minor. Some aren't. A cracked heat exchanger gets worse quickly and isn't cheap to fix if it's left.

⚠️ If water is near any electrical components, switch the boiler off at the mains and don't turn it back on. Call a heating engineer straight away.

Even a slow drip is worth getting looked at properly. The longer it's left, the more likely it is to cause damage elsewhere on the system. If you're based in the Dublin area and you're seeing water where it shouldn't be, get someone in sooner rather than later.

Repeated Lockouts

A boiler that keeps shutting itself down isn't necessarily broken. It's responding to something it's detected: low or high pressure, restricted flow, a faulty sensor or thermostat. The lockout is the boiler protecting itself. The problem is whatever's triggering it.

Bleed the radiators, check the pressure, reset and see what happens. If it cuts out again shortly after, the underlying issue hasn't been addressed, and continuing to reset without fixing the cause can wear out the pump or damage internal seals over time. If it's locking out repeatedly, it needs an engineer.

Strange Noises From the Boiler

Kettling is the most common one: a low rumbling or whistling that sounds like a kettle coming to the boil. It usually points to limescale or sludge inside the heat exchanger restricting water flow. As the flow reduces, water overheats in that section of the exchanger, and the noise is the result. It's more of an issue in hard water areas.

Left long enough, that kind of restriction can cause heat exchanger damage on top of the sludge problem, which means a flush and a component replacement rather than just a flush. Getting a magnetic filter fitted after the clean is a sensible follow-up to catch debris before it has a chance to build up again.

Radiators Cold at the Top

Trapped air is almost always the explanation here. As air collects at the top of the panel it stops hot water circulating through the full radiator, leaving the top cold while the bottom warms up normally. Bleeding the radiator releases the air pocket and gets everything moving again. You need a bleed key, it takes a few minutes, and it's one of the handful of things you can genuinely sort yourself without needing to call anyone.

Radiators Cold at the Bottom

A different problem entirely. Cold spots at the bottom of radiators point to sludge, which is iron oxide and debris that settles out of the water over time and sits at the base of the panel. Bleeding won't shift it. If it's isolated to one or two radiators a targeted flush might be enough, but if multiple radiators across the house are affected, a full powerflush of the system is usually the right call.

Boiler Not Responding to the Thermostat

Flat batteries in the thermostat cause this more often than you'd think. Replace them and see if the boiler responds. Also check the time and programme settings, particularly after a power cut, and confirm the thermostat temperature is set high enough to actually trigger a heating cycle.

Wireless thermostats can lose their pairing with the boiler receiver. If the stat is showing it's calling for heat but nothing's happening, re-pairing is usually covered in the manual and takes a few minutes. If the thermostat itself has failed, it needs replacing, which an engineer can confirm fairly quickly.

Frozen Condensate Pipe

A winter-only fault. The condensate pipe is a white plastic pipe that runs from the boiler to an outside drain, and it can freeze when temperatures drop. The boiler will usually shut down, often with a gurgling sound and an error code on the display.

Warming the pipe with warm water or a hot water bottle will usually clear the blockage. Don't use boiling water as it can split the pipe. Reset the boiler once it's thawed. If this becomes an annual problem, having the pipe lagged properly is a simple fix that takes the issue off the table for future winters.

Pilot Light Won't Stay Lit

On older boilers with a standing pilot light, a flame that keeps going out usually points to a worn thermocouple, a gas supply issue, or inadequate ventilation around the appliance. You can try relighting it following the instructions in the manual, but if it won't hold, that's where it ends. A pilot light that won't stay lit is telling you something is wrong with either the gas supply or a safety component, and that is a job for a registered gas engineer, not another attempt at a reset.

When to Call Straight Away

⚠️ If you smell gas, notice a strong burning or metallic smell, or see significant water inside the boiler casing, stop. Turn the boiler off at the mains if it's safe to do so and call a gas engineer immediately. In Ireland the gas emergency line is 1800 20 50 50.

Repeated lockouts with error codes you don't recognise, after the basic checks have been done, also fall into the same category. Resetting the boiler over and over without knowing why it's cutting out isn't a fix, and it isn't neutral either.

Based in Dublin? We Can Help

At EK Plumbing & Heating we cover boiler faults, breakdowns, and heating issues across Dublin and the surrounding areas. Whether it's something you can't pin down, a boiler overdue a service, or a replacement that keeps getting pushed back, get in touch through our contact page and we'll figure out what's going on. Make and model, any error codes, how long it's been happening — the more you can tell us, the quicker we can help.